Spring-Retry重试

时间:2022-06-03 ityml 人气:0

Spring Retry提供了自动重新调用失败的操作的功能。这在错误可能是暂时的（例如瞬时网络故障）的情况下很有用。从2.2.0版本开始，重试功能已从Spring Batch中撤出，成为一个独立的新库：Spring Retry

Maven依赖

<dependency>
    <groupId>org.springframework.retry</groupId>
    <artifactId>spring-retry</artifactId>
</dependency>
<!-- also need to add Spring AOP into our project-->
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aspects</artifactId>
</dependency>

注解使用

开启Retry功能

在启动类中使用@EnableRetry注解

package org.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.retry.annotation.EnableRetry;

@SpringBootApplication
@EnableRetry
public class RetryApp {

    public static void main(String[] args) {
        SpringApplication.run(RetryApp.class, args);
    }
}

注解`@Retryable`

需要在重试的代码中加入重试注解@Retryable

package org.example;

import lombok.extern.slf4j.Slf4j;
import org.springframework.retry.annotation.Backoff;
import org.springframework.retry.annotation.Recover;
import org.springframework.retry.annotation.Retryable;
import org.springframework.stereotype.Service;

import java.time.LocalDateTime;

@Service
@Slf4j
public class RetryService {

    @Retryable(value = IllegalAccessException.class)
    public void service1() throws IllegalAccessException {
        log.info("do something... {}", LocalDateTime.now());
        throw new IllegalAccessException("manual exception");
    }
}

默认情况下，会重试3次，间隔1秒

我们可以从注解@Retryable中看到

@Target({ ElementType.METHOD, ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Retryable {

	/**
	 * Retry interceptor bean name to be applied for retryable method. Is mutually
	 * exclusive with other attributes.
	 * @return the retry interceptor bean name
	 */
	String interceptor() default "";

	/**
	 * Exception types that are retryable. Synonym for includes(). Defaults to empty (and
	 * if excludes is also empty all exceptions are retried).
	 * @return exception types to retry
	 */
	Class<? extends Throwable>[] value() default {};

	/**
	 * Exception types that are retryable. Defaults to empty (and if excludes is also
	 * empty all exceptions are retried).
	 * @return exception types to retry
	 */
	Class<? extends Throwable>[] include() default {};

	/**
	 * Exception types that are not retryable. Defaults to empty (and if includes is also
	 * empty all exceptions are retried).
	 * If includes is empty but excludes is not, all not excluded exceptions are retried
	 * @return exception types not to retry
	 */
	Class<? extends Throwable>[] exclude() default {};

	/**
	 * A unique label for statistics reporting. If not provided the caller may choose to
	 * ignore it, or provide a default.
	 *
	 * @return the label for the statistics
	 */
	String label() default "";

	/**
	 * Flag to say that the retry is stateful: i.e. exceptions are re-thrown, but the
	 * retry policy is applied with the same policy to subsequent invocations with the
	 * same arguments. If false then retryable exceptions are not re-thrown.
	 * @return true if retry is stateful, default false
	 */
	boolean stateful() default false;

	/**
	 * @return the maximum number of attempts (including the first failure), defaults to 3
	 */
	int maxAttempts() default 3;  //默认重试次数3次

	/**
	 * @return an expression evaluated to the maximum number of attempts (including the first failure), defaults to 3
	 * Overrides {@link #maxAttempts()}.
	 * @since 1.2
	 */
	String maxAttemptsExpression() default "";

	/**
	 * Specify the backoff properties for retrying this operation. The default is a
	 * simple {@link Backoff} specification with no properties - see it's documentation
	 * for defaults.
	 * @return a backoff specification
	 */
	Backoff backoff() default @Backoff(); //默认的重试中的退避策略

	/**
	 * Specify an expression to be evaluated after the {@code SimpleRetryPolicy.canRetry()}
	 * returns true - can be used to conditionally suppress the retry. Only invoked after
	 * an exception is thrown. The root object for the evaluation is the last {@code Throwable}.
	 * Other beans in the context can be referenced.
	 * For example:
	 * <pre class=code>
	 *  {@code "message.contains('you can retry this')"}.
	 * </pre>
	 * and
	 * <pre class=code>
	 *  {@code "@someBean.shouldRetry(#root)"}.
	 * </pre>
	 * @return the expression.
	 * @since 1.2
	 */
	String exceptionExpression() default "";

	/**
	 * Bean names of retry listeners to use instead of default ones defined in Spring context
	 * @return retry listeners bean names
	 */
	String[] listeners() default {};

}

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Backoff {

	/**
	 * Synonym for {@link #delay()}.
	 *
	 * @return the delay in milliseconds (default 1000)
	 */
	long value() default 1000; //默认的重试间隔1秒

	/**
	 * A canonical backoff period. Used as an initial value in the exponential case, and
	 * as a minimum value in the uniform case.
	 * @return the initial or canonical backoff period in milliseconds (default 1000)
	 */
	long delay() default 0;

	/**
	 * The maximimum wait (in milliseconds) between retries. If less than the
	 * {@link #delay()} then the default of
	 * {@value org.springframework.retry.backoff.ExponentialBackOffPolicy#DEFAULT_MAX_INTERVAL}
	 * is applied.
	 *
	 * @return the maximum delay between retries (default 0 = ignored)
	 */
	long maxDelay() default 0;

	/**
	 * If positive, then used as a multiplier for generating the next delay for backoff.
	 *
	 * @return a multiplier to use to calculate the next backoff delay (default 0 =
	 * ignored)
	 */
	double multiplier() default 0;

	/**
	 * An expression evaluating to the canonical backoff period. Used as an initial value
	 * in the exponential case, and as a minimum value in the uniform case. Overrides
	 * {@link #delay()}.
	 * @return the initial or canonical backoff period in milliseconds.
	 * @since 1.2
	 */
	String delayExpression() default "";

	/**
	 * An expression evaluating to the maximimum wait (in milliseconds) between retries.
	 * If less than the {@link #delay()} then the default of
	 * {@value org.springframework.retry.backoff.ExponentialBackOffPolicy#DEFAULT_MAX_INTERVAL}
	 * is applied. Overrides {@link #maxDelay()}
	 *
	 * @return the maximum delay between retries (default 0 = ignored)
	 * @since 1.2
	 */
	String maxDelayExpression() default "";

	/**
	 * Evaluates to a vaule used as a multiplier for generating the next delay for
	 * backoff. Overrides {@link #multiplier()}.
	 *
	 * @return a multiplier expression to use to calculate the next backoff delay (default
	 * 0 = ignored)
	 * @since 1.2
	 */
	String multiplierExpression() default "";

	/**
	 * In the exponential case ({@link #multiplier()} &gt; 0) set this to true to have the
	 * backoff delays randomized, so that the maximum delay is multiplier times the
	 * previous delay and the distribution is uniform between the two values.
	 *
	 * @return the flag to signal randomization is required (default false)
	 */
	boolean random() default false;

}

我们来运行测试代码

package org.example;


import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;

@SpringBootTest
class RetryServiceTest {

    @Autowired
    private RetryService retryService;

    @Test
    void testService1() throws IllegalAccessException {
        retryService.service1();
    }
}

运行结果如下：

2021-01-05 19:40:41.221 INFO 3548 --- [ main] org.example.RetryService : do something... 2021-01-05T19:40:41.221763300
2021-01-05 19:40:42.224 INFO 3548 --- [ main] org.example.RetryService : do something... 2021-01-05T19:40:42.224436500
2021-01-05 19:40:43.225 INFO 3548 --- [ main] org.example.RetryService : do something... 2021-01-05T19:40:43.225189300

java.lang.IllegalAccessException: manual exception

   at org.example.RetryService.service1(RetryService.java:19)
   at org.example.RetryService$$FastClassBySpringCGLIB$$c0995ddb.invoke(<generated>)
   at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)
   at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:769)
   at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163)
   at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747)
   at org.springframework.retry.interceptor.RetryOperationsInterceptor$1.doWithRetry(RetryOperationsInterceptor.java:91)
   at org.springframework.retry.support.RetryTemplate.doExecute(RetryTemplate.java:287)
   at org.springframework.retry.support.RetryTemplate.execute(RetryTemplate.java:164)
   at org.springframework.retry.interceptor.RetryOperationsInterceptor.invoke(RetryOperationsInterceptor.java:118)
   at org.springframework.retry.annotation.AnnotationAwareRetryOperationsInterceptor.invoke(AnnotationAwareRetryOperationsInterceptor.java:153)
   at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
   at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:747)
   at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:689)
   at org.example.RetryService$$EnhancerBySpringCGLIB$$499afa1d.service1(<generated>)
   at org.example.RetryServiceTest.testService1(RetryServiceTest.java:16)
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
   at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.base/java.lang.reflect.Method.invoke(Method.java:566)
   at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:675)
   at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
   at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:125)
   at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:132)
   at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:124)
   at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:74)
   at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
   at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
   at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:104)
   at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:62)
   at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:43)
   at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:35)
   at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
   at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
   at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:202)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:198)
   at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:135)
   at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:69)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:135)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
   at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
   at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)
   at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
   at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
   at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)
   at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
   at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
   at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
   at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
   at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
   at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:229)
   at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$6(DefaultLauncher.java:197)
   at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:211)
   at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:191)
   at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:128)
   at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71)
   at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
   at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220)
   at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53)

可以看到重新执行了3次service1()方法，然后间隔是1秒，然后最后还是重试失败，所以抛出了异常

既然我们看到了注解@Retryable中有这么多参数可以设置，那我们就来介绍几个常用的配置。

@Retryable(include = IllegalAccessException.class, maxAttempts = 5)
public void service2() throws IllegalAccessException {
    log.info("do something... {}", LocalDateTime.now());
    throw new IllegalAccessException("manual exception");
}

首先是maxAttempts，用于设置重试次数

2021-01-06 09:30:11.263 INFO 15612 --- [ main] org.example.RetryService : do something... 2021-01-06T09:30:11.263621900
2021-01-06 09:30:12.265 INFO 15612 --- [ main] org.example.RetryService : do something... 2021-01-06T09:30:12.265629100
2021-01-06 09:30:13.265 INFO 15612 --- [ main] org.example.RetryService : do something... 2021-01-06T09:30:13.265701
2021-01-06 09:30:14.266 INFO 15612 --- [ main] org.example.RetryService : do something... 2021-01-06T09:30:14.266705400
2021-01-06 09:30:15.266 INFO 15612 --- [ main] org.example.RetryService : do something... 2021-01-06T09:30:15.266733200

java.lang.IllegalAccessException: manual exception
....

从运行结果可以看到，方法执行了5次。

下面来介绍maxAttemptsExpression的设置

@Retryable(value = IllegalAccessException.class, maxAttemptsExpression = "${maxAttempts}")
public void service3() throws IllegalAccessException {
    log.info("do something... {}", LocalDateTime.now());
    throw new IllegalAccessException("manual exception");
}

maxAttemptsExpression则可以使用表达式，比如上述就是通过获取配置中maxAttempts的值，我们可以在application.yml设置。上述其实省略掉了SpEL表达式#{....}，运行结果的话可以发现方法执行了4次..

maxAttempts: 4

我们可以使用SpEL表达式

@Retryable(value = IllegalAccessException.class, maxAttemptsExpression = "#{1+1}")
public void service3_1() throws IllegalAccessException {
    log.info("do something... {}", LocalDateTime.now());
    throw new IllegalAccessException("manual exception");
}

@Retryable(value = IllegalAccessException.class, maxAttemptsExpression = "#{${maxAttempts}}")//效果和上面的一样
public void service3_2() throws IllegalAccessException {
    log.info("do something... {}", LocalDateTime.now());
    throw new IllegalAccessException("manual exception");
}

接着我们下面来看看exceptionExpression, 一样也是写SpEL表达式

@Retryable(value = IllegalAccessException.class, exceptionExpression = "message.contains('test')")
public void service4(String exceptionMessage) throws IllegalAccessException {
    log.info("do something... {}", LocalDateTime.now());
    throw new IllegalAccessException(exceptionMessage);
}

    @Retryable(value = IllegalAccessException.class, exceptionExpression = "#{message.contains('test')}")
public void service4_3(String exceptionMessage) throws IllegalAccessException {
    log.info("do something... {}", LocalDateTime.now());
    throw new IllegalAccessException(exceptionMessage);
}

上面的表达式exceptionExpression = "message.contains('test')"的作用其实是获取到抛出来exception的message(调用了getMessage()方法)，然后判断message的内容里面是否包含了test字符串，如果包含的话就会执行重试。所以如果调用方法的时候传入的参数exceptionMessage中包含了test字符串的话就会执行重试。

但这里值得注意的是, Spring Retry 1.2.5之后exceptionExpression是可以省略掉#{...}

Since Spring Retry 1.2.5, for exceptionExpression, templated expressions (#{...}) are deprecated in favor of simple expression strings (message.contains('this can be retried')).

使用1.2.5之后的版本运行是没有问题的

<dependency>
    <groupId>org.springframework.retry</groupId>
    <artifactId>spring-retry</artifactId>
    <version>1.3.0</version>
</dependency>

但是如果使用1.2.5版本之前包括1.2.5版本的话，运行的时候会报错如下：

2021-01-06 09:52:45.209 INFO 23220 --- [ main] org.example.RetryService : do something... 2021-01-06T09:52:45.209178200

org.springframework.expression.spel.SpelEvaluationException: EL1001E: Type conversion problem, cannot convert from java.lang.String to java.lang.Boolean

   at org.springframework.expression.spel.support.StandardTypeConverter.convertValue(StandardTypeConverter.java:75)
   at org.springframework.expression.common.ExpressionUtils.convertTypedValue(ExpressionUtils.java:57)
   at org.springframework.expression.common.LiteralExpression.getValue(LiteralExpression.java:106)
   at org.springframework.retry.policy.ExpressionRetryPolicy.canRetry(ExpressionRetryPolicy.java:113)
   at org.springframework.retry.support.RetryTemplate.canRetry(RetryTemplate.java:375)
   at org.springframework.retry.support.RetryTemplate.doExecute(RetryTemplate.java:304)
   at org.springframework.retry.support.RetryTemplate.execute(RetryTemplate.java:164)
   at org.springframework.retry.interceptor.RetryOperationsInterceptor.invoke(RetryOperationsInterceptor.java:118)
   at org.springframework.retry.annotation.AnnotationAwareRetryOperationsInterceptor.invoke(AnnotationAwareRetryOperationsInterceptor.java:153)
   at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186)
   at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:749)
   at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:691)
   at org.example.RetryService$$EnhancerBySpringCGLIB$$d321a75e.service4(<generated>)
   at org.example.RetryServiceTest.testService4_2(RetryServiceTest.java:46)
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
   at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.base/java.lang.reflect.Method.invoke(Method.java:566)
   at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:686)
   at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
   at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
   at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
   at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
   at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
   at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
   at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
   at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
   at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
   at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
   at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
   at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
   at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
   at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:212)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:208)
   at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:137)
   at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:71)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:135)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
   at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
   at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)
   at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
   at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
   at java.base/java.util.ArrayList.forEach(ArrayList.java:1540)
   at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:125)
   at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:135)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:123)
   at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:122)
   at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:80)
   at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
   at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
   at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
   at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:248)
   at org.junit.platform.launcher.core.DefaultLauncher.lambda$execute$5(DefaultLauncher.java:211)
   at org.junit.platform.launcher.core.DefaultLauncher.withInterceptedStreams(DefaultLauncher.java:226)
   at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:199)
   at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:132)
   at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71)
   at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
   at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220)
   at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53)
Caused by: org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [java.lang.Boolean] for value 'message.contains('test')'; nested exception is java.lang.IllegalArgumentException: Invalid boolean value 'message.contains('test')'
   at org.springframework.core.convert.support.ConversionUtils.invokeConverter(ConversionUtils.java:47)
   at org.springframework.core.convert.support.GenericConversionService.convert(GenericConversionService.java:191)
   at org.springframework.expression.spel.support.StandardTypeConverter.convertValue(StandardTypeConverter.java:70)
   ... 76 more
Caused by: java.lang.IllegalArgumentException: Invalid boolean value 'message.contains('test')'
   at org.springframework.core.convert.support.StringToBooleanConverter.convert(StringToBooleanConverter.java:63)
   at org.springframework.core.convert.support.StringToBooleanConverter.convert(StringToBooleanConverter.java:31)
   at org.springframework.core.convert.support.GenericConversionService$ConverterAdapter.convert(GenericConversionService.java:385)
   at org.springframework.core.convert.support.ConversionUtils.invokeConverter(ConversionUtils.java:41)
   ... 78 more

还可以在表达式中执行一个方法，前提是方法的类在spring容器中注册了，@retryService其实就是获取bean name为retryService的bean，然后调用里面的checkException方法，传入的参数为#root，它其实就是抛出来的exception对象。一样的也是可以省略#{...}

    @Retryable(value = IllegalAccessException.class, exceptionExpression = "#{@retryService.checkException(#root)}")
    public void service5(String exceptionMessage) throws IllegalAccessException {
        log.info("do something... {}", LocalDateTime.now());
        throw new IllegalAccessException(exceptionMessage);
    }

    @Retryable(value = IllegalAccessException.class, exceptionExpression = "@retryService.checkException(#root)")
    public void service5_1(String exceptionMessage) throws IllegalAccessException {
        log.info("do something... {}", LocalDateTime.now());
        throw new IllegalAccessException(exceptionMessage);
    }
    
    public boolean checkException(Exception e) {
        log.error("error message:{}", e.getMessage());
        return true; //返回true的话表明会执行重试，如果返回false则不会执行重试
    }

运行结果：

2021-01-06 13:33:52.913 INFO 23052 --- [ main] org.example.RetryService : do something... 2021-01-06T13:33:52.913404
2021-01-06 13:33:52.981 ERROR 23052 --- [ main] org.example.RetryService : error message:test message
2021-01-06 13:33:53.990 ERROR 23052 --- [ main] org.example.RetryService : error message:test message
2021-01-06 13:33:53.990 INFO 23052 --- [ main] org.example.RetryService : do something... 2021-01-06T13:33:53.990947400
2021-01-06 13:33:53.990 ERROR 23052 --- [ main] org.example.RetryService : error message:test message
2021-01-06 13:33:54.992 ERROR 23052 --- [ main] org.example.RetryService : error message:test message
2021-01-06 13:33:54.992 INFO 23052 --- [ main] org.example.RetryService : do something... 2021-01-06T13:33:54.992342900

当然还有更多表达式的用法了...

	@Retryable(exceptionExpression = "#{#root instanceof T(java.lang.IllegalAccessException)}") //判断exception的类型
    public void service5_2(String exceptionMessage) {
        log.info("do something... {}", LocalDateTime.now());
        throw new NullPointerException(exceptionMessage);
    }

    @Retryable(exceptionExpression = "#root instanceof T(java.lang.IllegalAccessException)")
    public void service5_3(String exceptionMessage) {
        log.info("do something... {}", LocalDateTime.now());
        throw new NullPointerException(exceptionMessage);
    }

    @Retryable(exceptionExpression = "myMessage.contains('test')") //查看自定义的MyException中的myMessage的值是否包含test字符串
    public void service5_4(String exceptionMessage) throws MyException {
        log.info("do something... {}", LocalDateTime.now());
        throw new MyException(exceptionMessage); //自定义的exception
    }

    @Retryable(exceptionExpression = "#root.myMessage.contains('test')")  //和上面service5_4方法的效果一样
    public void service5_5(String exceptionMessage) throws MyException {
        log.info("do something... {}", LocalDateTime.now());
        throw new MyException(exceptionMessage);
    }

package org.example;

import lombok.Getter;
import lombok.Setter;

@Getter
@Setter
public class MyException extends Exception {
    private String myMessage;

    public MyException(String myMessage) {
        this.myMessage = myMessage;
    }
}

下面再来看看另一个配置exclude

  @Retryable(exclude = MyException.class)
    public void service6(String exceptionMessage) throws MyException {
        log.info("do something... {}", LocalDateTime.now());
        throw new MyException(exceptionMessage);
    }

这个exclude属性可以帮我们排除一些我们不想重试的异常

最后我们来看看这个backoff 重试等待策略, 默认使用@Backoff注解。

我们先来看看这个@Backoff的value属性,用于设置重试间隔

 @Retryable(value = IllegalAccessException.class,
            backoff = @Backoff(value = 2000))
    public void service7() throws IllegalAccessException {
        log.info("do something... {}", LocalDateTime.now());
        throw new IllegalAccessException();
    }

运行结果可以看出来重试的间隔为2秒

2021-01-06 14:47:38.036 INFO 21116 --- [ main] org.example.RetryService : do something... 2021-01-06T14:47:38.036732600
2021-01-06 14:47:40.038 INFO 21116 --- [ main] org.example.RetryService : do something... 2021-01-06T14:47:40.037753600
2021-01-06 14:47:42.046 INFO 21116 --- [ main] org.example.RetryService : do something... 2021-01-06T14:47:42.046642900

java.lang.IllegalAccessException
at org.example.RetryService.service7(RetryService.java:113)
...

接下来介绍@Backoff的delay属性，它与value属性不能共存，当delay不设置的时候会去读value属性设置的值，如果delay设置的话则会忽略value属性

@Retryable(value = IllegalAccessException.class,
            backoff = @Backoff(value = 2000,delay = 500))
    public void service8() throws IllegalAccessException {
        log.info("do something... {}", LocalDateTime.now());
        throw new IllegalAccessException();
    }

运行结果可以看出，重试的时间间隔为500ms

2021-01-06 15:22:42.271 INFO 13512 --- [ main] org.example.RetryService : do something... 2021-01-06T15:22:42.271504800
2021-01-06 15:22:42.772 INFO 13512 --- [ main] org.example.RetryService : do something... 2021-01-06T15:22:42.772234900
2021-01-06 15:22:43.273 INFO 13512 --- [ main] org.example.RetryService : do something... 2021-01-06T15:22:43.273246700

java.lang.IllegalAccessException
at org.example.RetryService.service8(RetryService.java:121)

接下来我们来看``@Backoff的multiplier`的属性, 指定延迟倍数, 默认为0。

@Retryable(value = IllegalAccessException.class,maxAttempts = 4,
            backoff = @Backoff(delay = 2000, multiplier = 2))
    public void service9() throws IllegalAccessException {
        log.info("do something... {}", LocalDateTime.now());
        throw new IllegalAccessException();
    }

multiplier设置为2，则表示第一次重试间隔为2s，第二次为4秒，第三次为8s

运行结果如下：

2021-01-06 15:58:07.458 INFO 23640 --- [ main] org.example.RetryService : do something... 2021-01-06T15:58:07.458245500
2021-01-06 15:58:09.478 INFO 23640 --- [ main] org.example.RetryService : do something... 2021-01-06T15:58:09.478681300
2021-01-06 15:58:13.478 INFO 23640 --- [ main] org.example.RetryService : do something... 2021-01-06T15:58:13.478921900
2021-01-06 15:58:21.489 INFO 23640 --- [ main] org.example.RetryService : do something... 2021-01-06T15:58:21.489240600

java.lang.IllegalAccessException
at org.example.RetryService.service9(RetryService.java:128)
...

接下来我们来看看这个@Backoff的maxDelay属性,设置最大的重试间隔，当超过这个最大的重试间隔的时候，重试的间隔就等于maxDelay的值

@Retryable(value = IllegalAccessException.class,maxAttempts = 4,
            backoff = @Backoff(delay = 2000, multiplier = 2,maxDelay = 5000))
    public void service10() throws IllegalAccessException {
        log.info("do something... {}", LocalDateTime.now());
        throw new IllegalAccessException();
    }

运行结果：

2021-01-06 16:12:37.377 INFO 5024 --- [ main] org.example.RetryService : do something... 2021-01-06T16:12:37.377616100
2021-01-06 16:12:39.381 INFO 5024 --- [ main] org.example.RetryService : do something... 2021-01-06T16:12:39.381299400
2021-01-06 16:12:43.382 INFO 5024 --- [ main] org.example.RetryService : do something... 2021-01-06T16:12:43.382169500
2021-01-06 16:12:48.396 INFO 5024 --- [ main] org.example.RetryService : do something... 2021-01-06T16:12:48.396327600

java.lang.IllegalAccessException
at org.example.RetryService.service10(RetryService.java:135)

可以最后的最大重试间隔是5秒

注解`@Recover`

当@Retryable方法重试失败之后，最后就会调用@Recover方法。用于@Retryable失败时的“兜底”处理方法。 @Recover的方法必须要与@Retryable注解的方法保持一致，第一入参为要重试的异常，其他参数与@Retryable保持一致，返回值也要一样，否则无法执行！

	@Retryable(value = IllegalAccessException.class)
    public void service11() throws IllegalAccessException {
        log.info("do something... {}", LocalDateTime.now());
        throw new IllegalAccessException();
    }


    @Recover
    public void recover11(IllegalAccessException e) {
        log.info("service retry after Recover => {}", e.getMessage());
    }

    //=========================

    @Retryable(value = ArithmeticException.class)
    public int service12() throws IllegalAccessException {
        log.info("do something... {}", LocalDateTime.now());
        return 1 / 0;
    }


    @Recover
    public int recover12(ArithmeticException e) {
        log.info("service retry after Recover => {}", e.getMessage());
        return 0;
    }


    //=========================

    @Retryable(value = ArithmeticException.class)
    public int service13(String message) throws IllegalAccessException {
        log.info("do something... {},{}", message, LocalDateTime.now());
        return 1 / 0;
    }


    @Recover
    public int recover13(ArithmeticException e, String message) {
        log.info("{},service retry after Recover => {}", message, e.getMessage());
        return 0;
    }

注解`@CircuitBreaker`

熔断模式：指在具体的重试机制下失败后打开断路器，过了一段时间，断路器进入半开状态，允许一个进入重试，若失败再次进入断路器，成功则关闭断路器，注解为@CircuitBreaker,具体包括熔断打开时间、重置过期时间

	// openTimeout时间范围内失败maxAttempts次数后，熔断打开resetTimeout时长 
	@CircuitBreaker(openTimeout = 1000, resetTimeout = 3000, value = NullPointerException.class)
    public void circuitBreaker(int num) {
        log.info(" 进入断路器方法num={}", num);
        if (num > 8) return;
        Integer n = null;
        System.err.println(1 / n);
    }


    @Recover
    public void recover(NullPointerException e) {
        log.info("service retry after Recover => {}", e.getMessage());
    }

测试方法

	@Test
    public void testCircuitBreaker() throws InterruptedException {
        System.err.println("尝试进入断路器方法，并触发异常...");
        retryService.circuitBreaker(1);
        retryService.circuitBreaker(1);
        retryService.circuitBreaker(9);
        retryService.circuitBreaker(9);
        System.err.println("在openTimeout 1秒之内重试次数为2次，未达到触发熔断, 断路器依然闭合...");
        TimeUnit.SECONDS.sleep(1);
        System.err.println("超过openTimeout 1秒之后, 因为未触发熔断，所以重试次数重置，可以正常访问...,继续重试3次方法...");
        retryService.circuitBreaker(1);
        retryService.circuitBreaker(1);
        retryService.circuitBreaker(1);
        System.err.println("在openTimeout 1秒之内重试次数为3次，达到触发熔断，不会执行重试，只会执行恢复方法...");
        retryService.circuitBreaker(1);
        TimeUnit.SECONDS.sleep(2);
        retryService.circuitBreaker(9);
        TimeUnit.SECONDS.sleep(3);
        System.err.println("超过resetTimeout 3秒之后，断路器重新闭合...,可以正常访问");
        retryService.circuitBreaker(9);
        retryService.circuitBreaker(9);
        retryService.circuitBreaker(9);
        retryService.circuitBreaker(9);
        retryService.circuitBreaker(9);

    }

运行结果：

尝试进入断路器方法，并触发异常...
2021-01-07 21:44:20.842 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=1
2021-01-07 21:44:20.844 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null
2021-01-07 21:44:20.845 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=1
2021-01-07 21:44:20.845 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null
2021-01-07 21:44:20.845 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9
2021-01-07 21:44:20.845 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9
在openTimeout 1秒之内重试次数为2次，未达到触发熔断, 断路器依然闭合...
超过openTimeout 1秒之后, 因为未触发熔断，所以重试次数重置，可以正常访问...,继续重试3次方法...
2021-01-07 21:44:21.846 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=1
2021-01-07 21:44:21.847 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null
2021-01-07 21:44:21.847 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=1
2021-01-07 21:44:21.847 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null
2021-01-07 21:44:21.847 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=1
2021-01-07 21:44:21.848 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null
在openTimeout 1秒之内重试次数为3次，达到触发熔断，不会执行重试，只会执行恢复方法...
2021-01-07 21:44:21.848 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null
2021-01-07 21:44:23.853 INFO 7464 --- [ main] org.example.RetryService : service retry after Recover => null
超过resetTimeout 3秒之后，断路器重新闭合...,可以正常访问
2021-01-07 21:44:26.853 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9
2021-01-07 21:44:26.854 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9
2021-01-07 21:44:26.855 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9
2021-01-07 21:44:26.855 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9
2021-01-07 21:44:26.856 INFO 7464 --- [ main] org.example.RetryService : 进入断路器方法num=9

RetryTemplate

RetryTemplate配置

package org.example;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.retry.backoff.FixedBackOffPolicy;
import org.springframework.retry.policy.SimpleRetryPolicy;
import org.springframework.retry.support.RetryTemplate;

@Configuration
public class AppConfig {
   
    @Bean
    public RetryTemplate retryTemplate() {
        RetryTemplate retryTemplate = new RetryTemplate();

        SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy(); //设置重试策略
        retryPolicy.setMaxAttempts(2);
        retryTemplate.setRetryPolicy(retryPolicy);


        FixedBackOffPolicy fixedBackOffPolicy = new FixedBackOffPolicy(); //设置退避策略
        fixedBackOffPolicy.setBackOffPeriod(2000L);
        retryTemplate.setBackOffPolicy(fixedBackOffPolicy);
		
        return retryTemplate;
    }
}

可以看到这些配置跟我们直接写注解的方式是差不多的，这里就不过多的介绍了。。

使用RetryTemplate

package org.example;

import org.junit.jupiter.api.Test;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.retry.RetryCallback;
import org.springframework.retry.RetryContext;
import org.springframework.retry.support.RetryTemplate;

@SpringBootTest
public class RetryTemplateTest {

    @Autowired
    private RetryTemplate retryTemplate;

    @Autowired
    private RetryTemplateService retryTemplateService;

    @Test
    void test1() throws IllegalAccessException {
        retryTemplate.execute(new RetryCallback<Object, IllegalAccessException>() {
            @Override
            public Object doWithRetry(RetryContext context) throws IllegalAccessException {
                 retryTemplateService.service1();
                return null;
            }
        });
    }
    
    @Test
    void test2() throws IllegalAccessException {
        retryTemplate.execute(new RetryCallback<Object, IllegalAccessException>() {
            @Override
            public Object doWithRetry(RetryContext context) throws IllegalAccessException {
                retryTemplateService.service1();
                return null;
            }
        }, new RecoveryCallback<Object>() {
            @Override
            public Object recover(RetryContext context) throws Exception {
                log.info("RecoveryCallback....");
                return null;
            }
        });
    }
}

RetryOperations定义重试的API，RetryTemplate是API的模板模式实现，实现了重试和熔断。提供的API如下:

package org.springframework.retry;

import org.springframework.retry.support.DefaultRetryState;

/**
 * Defines the basic set of operations implemented by {@link RetryOperations} to execute
 * operations with configurable retry behaviour.
 *
 * @author Rob Harrop
 * @author Dave Syer
 */
public interface RetryOperations {

	/**
	 * Execute the supplied {@link RetryCallback} with the configured retry semantics. See
	 * implementations for configuration details.
	 * @param <T> the return value
	 * @param retryCallback the {@link RetryCallback}
	 * @param <E> the exception to throw
	 * @return the value returned by the {@link RetryCallback} upon successful invocation.
	 * @throws E any {@link Exception} raised by the {@link RetryCallback} upon
	 * unsuccessful retry.
	 * @throws E the exception thrown
	 */
	<T, E extends Throwable> T execute(RetryCallback<T, E> retryCallback) throws E;

	/**
	 * Execute the supplied {@link RetryCallback} with a fallback on exhausted retry to
	 * the {@link RecoveryCallback}. See implementations for configuration details.
	 * @param recoveryCallback the {@link RecoveryCallback}
	 * @param retryCallback the {@link RetryCallback} {@link RecoveryCallback} upon
	 * @param <T> the type to return
	 * @param <E> the type of the exception
	 * @return the value returned by the {@link RetryCallback} upon successful invocation,
	 * and that returned by the {@link RecoveryCallback} otherwise.
	 * @throws E any {@link Exception} raised by the unsuccessful retry.
	 */
	<T, E extends Throwable> T execute(RetryCallback<T, E> retryCallback, RecoveryCallback<T> recoveryCallback)
			throws E;

	/**
	 * A simple stateful retry. Execute the supplied {@link RetryCallback} with a target
	 * object for the attempt identified by the {@link DefaultRetryState}. Exceptions
	 * thrown by the callback are always propagated immediately so the state is required
	 * to be able to identify the previous attempt, if there is one - hence the state is
	 * required. Normal patterns would see this method being used inside a transaction,
	 * where the callback might invalidate the transaction if it fails.
	 *
	 * See implementations for configuration details.
	 * @param retryCallback the {@link RetryCallback}
	 * @param retryState the {@link RetryState}
	 * @param <T> the type of the return value
	 * @param <E> the type of the exception to return
	 * @return the value returned by the {@link RetryCallback} upon successful invocation,
	 * and that returned by the {@link RecoveryCallback} otherwise.
	 * @throws E any {@link Exception} raised by the {@link RecoveryCallback}.
	 * @throws ExhaustedRetryException if the last attempt for this state has already been
	 * reached
	 */
	<T, E extends Throwable> T execute(RetryCallback<T, E> retryCallback, RetryState retryState)
			throws E, ExhaustedRetryException;

	/**
	 * A stateful retry with a recovery path. Execute the supplied {@link RetryCallback}
	 * with a fallback on exhausted retry to the {@link RecoveryCallback} and a target
	 * object for the retry attempt identified by the {@link DefaultRetryState}.
	 * @param recoveryCallback the {@link RecoveryCallback}
	 * @param retryState the {@link RetryState}
	 * @param retryCallback the {@link RetryCallback}
	 * @param <T> the return value type
	 * @param <E> the exception type
	 * @see #execute(RetryCallback, RetryState)
	 * @return the value returned by the {@link RetryCallback} upon successful invocation,
	 * and that returned by the {@link RecoveryCallback} otherwise.
	 * @throws E any {@link Exception} raised by the {@link RecoveryCallback} upon
	 * unsuccessful retry.
	 */
	<T, E extends Throwable> T execute(RetryCallback<T, E> retryCallback, RecoveryCallback<T> recoveryCallback,
			RetryState retryState) throws E;

}

下面主要介绍一下RetryTemplate配置的时候，需要设置的重试策略和退避策略

RetryPolicy

RetryPolicy是一个接口, 然后有很多具体的实现，我们先来看看它的接口中定义了什么方法

package org.springframework.retry;

import java.io.Serializable;

/**
 * A {@link RetryPolicy} is responsible for allocating and managing resources needed by
 * {@link RetryOperations}. The {@link RetryPolicy} allows retry operations to be aware of
 * their context. Context can be internal to the retry framework, e.g. to support nested
 * retries. Context can also be external, and the {@link RetryPolicy} provides a uniform
 * API for a range of different platforms for the external context.
 *
 * @author Dave Syer
 *
 */
public interface RetryPolicy extends Serializable {

	/**
	 * @param context the current retry status
	 * @return true if the operation can proceed
	 */
	boolean canRetry(RetryContext context); 

	/**
	 * Acquire resources needed for the retry operation. The callback is passed in so that
	 * marker interfaces can be used and a manager can collaborate with the callback to
	 * set up some state in the status token.
	 * @param parent the parent context if we are in a nested retry.
	 * @return a {@link RetryContext} object specific to this policy.
	 *
	 */
	RetryContext open(RetryContext parent);

	/**
	 * @param context a retry status created by the {@link #open(RetryContext)} method of
	 * this policy.
	 */
	void close(RetryContext context);

	/**
	 * Called once per retry attempt, after the callback fails.
	 * @param context the current status object.
	 * @param throwable the exception to throw
	 */
	void registerThrowable(RetryContext context, Throwable throwable);

}

我们来看看他有什么具体的实现类

SimpleRetryPolicy 默认最多重试3次
TimeoutRetryPolicy 默认在1秒内失败都会重试
ExpressionRetryPolicy 符合表达式就会重试
CircuitBreakerRetryPolicy 增加了熔断的机制，如果不在熔断状态，则允许重试
CompositeRetryPolicy 可以组合多个重试策略
NeverRetryPolicy 从不重试（也是一种重试策略哈）
AlwaysRetryPolicy 总是重试
等等...

BackOffPolicy

看一下退避策略，退避是指怎么去做下一次的重试，在这里其实就是等待多长时间。

FixedBackOffPolicy 默认固定延迟1秒后执行下一次重试
ExponentialBackOffPolicy 指数递增延迟执行重试，默认初始0.1秒，系数是2，那么下次延迟0.2秒，再下次就是延迟0.4秒，如此类推，最大30秒。
ExponentialRandomBackOffPolicy 在上面那个策略上增加随机性
UniformRandomBackOffPolicy 这个跟上面的区别就是，上面的延迟会不停递增，这个只会在固定的区间随机
StatelessBackOffPolicy 这个说明是无状态的，所谓无状态就是对上次的退避无感知，从它下面的子类也能看出来
等等...

RetryListener

listener可以监听重试，并执行对应的回调方法

package org.springframework.retry;

/**
 * Interface for listener that can be used to add behaviour to a retry. Implementations of
 * {@link RetryOperations} can chose to issue callbacks to an interceptor during the retry
 * lifecycle.
 *
 * @author Dave Syer
 *
 */
public interface RetryListener {

	/**
	 * Called before the first attempt in a retry. For instance, implementers can set up
	 * state that is needed by the policies in the {@link RetryOperations}. The whole
	 * retry can be vetoed by returning false from this method, in which case a
	 * {@link TerminatedRetryException} will be thrown.
	 * @param <T> the type of object returned by the callback
	 * @param <E> the type of exception it declares may be thrown
	 * @param context the current {@link RetryContext}.
	 * @param callback the current {@link RetryCallback}.
	 * @return true if the retry should proceed.
	 */
	<T, E extends Throwable> boolean open(RetryContext context, RetryCallback<T, E> callback);

	/**
	 * Called after the final attempt (successful or not). Allow the interceptor to clean
	 * up any resource it is holding before control returns to the retry caller.
	 * @param context the current {@link RetryContext}.
	 * @param callback the current {@link RetryCallback}.
	 * @param throwable the last exception that was thrown by the callback.
	 * @param <E> the exception type
	 * @param <T> the return value
	 */
	<T, E extends Throwable> void close(RetryContext context, RetryCallback<T, E> callback, Throwable throwable);

	/**
	 * Called after every unsuccessful attempt at a retry.
	 * @param context the current {@link RetryContext}.
	 * @param callback the current {@link RetryCallback}.
	 * @param throwable the last exception that was thrown by the callback.
	 * @param <T> the return value
	 * @param <E> the exception to throw
	 */
	<T, E extends Throwable> void onError(RetryContext context, RetryCallback<T, E> callback, Throwable throwable);

}

使用如下：

自定义一个Listener

package org.example;

import lombok.extern.slf4j.Slf4j;
import org.springframework.retry.RetryCallback;
import org.springframework.retry.RetryContext;
import org.springframework.retry.listener.RetryListenerSupport;

@Slf4j
public class DefaultListenerSupport extends RetryListenerSupport {
    @Override
    public <T, E extends Throwable> void close(RetryContext context,
                                               RetryCallback<T, E> callback, Throwable throwable) {
        log.info("onClose");
        super.close(context, callback, throwable);
    }

    @Override
    public <T, E extends Throwable> void onError(RetryContext context,
                                                 RetryCallback<T, E> callback, Throwable throwable) {
        log.info("onError");
        super.onError(context, callback, throwable);
    }

    @Override
    public <T, E extends Throwable> boolean open(RetryContext context,
                                                 RetryCallback<T, E> callback) {
        log.info("onOpen");
        return super.open(context, callback);
    }
}

把listener设置到retryTemplate中

package org.example;

import lombok.extern.slf4j.Slf4j;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.retry.backoff.FixedBackOffPolicy;
import org.springframework.retry.policy.SimpleRetryPolicy;
import org.springframework.retry.support.RetryTemplate;

@Configuration
@Slf4j
public class AppConfig {

    @Bean
    public RetryTemplate retryTemplate() {
        RetryTemplate retryTemplate = new RetryTemplate();

        SimpleRetryPolicy retryPolicy = new SimpleRetryPolicy(); //设置重试策略
        retryPolicy.setMaxAttempts(2);
        retryTemplate.setRetryPolicy(retryPolicy);


        FixedBackOffPolicy fixedBackOffPolicy = new FixedBackOffPolicy(); //设置退避策略
        fixedBackOffPolicy.setBackOffPeriod(2000L);
        retryTemplate.setBackOffPolicy(fixedBackOffPolicy);
        retryTemplate.registerListener(new DefaultListenerSupport()); //设置retryListener
        return retryTemplate;
    }
}

测试结果：

2021-01-08 10:48:05.663 INFO 20956 --- [ main] org.example.DefaultListenerSupport : onOpen
2021-01-08 10:48:05.663 INFO 20956 --- [ main] org.example.RetryTemplateService : do something...
2021-01-08 10:48:05.663 INFO 20956 --- [ main] org.example.DefaultListenerSupport : onError
2021-01-08 10:48:07.664 INFO 20956 --- [ main] org.example.RetryTemplateService : do something...
2021-01-08 10:48:07.664 INFO 20956 --- [ main] org.example.DefaultListenerSupport : onError
2021-01-08 10:48:07.664 INFO 20956 --- [ main] org.example.RetryTemplateTest : RecoveryCallback....
2021-01-08 10:48:07.664 INFO 20956 --- [ main] org.example.DefaultListenerSupport : onClose