springboot自动装配 浅谈springboot自动装配原理
向天再借500年 人气:0一、SpringBootApplication
@Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @SpringBootConfiguration @EnableAutoConfiguration @ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class), @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) }) public @interface SpringBootApplication {
@Target(ElementType.TYPE)
设置当前注解可以标记在哪里,而SpringBootApplication只能用在类上面
还有一些其他的设置
public enum ElementType { /** Class, interface (including annotation type), or enum declaration */ TYPE, /** Field declaration (includes enum constants) */ FIELD, /** Method declaration */ METHOD, /** Formal parameter declaration */ PARAMETER, /** Constructor declaration */ CONSTRUCTOR, /** Local variable declaration */ LOCAL_VARIABLE, /** Annotation type declaration */ ANNOTATION_TYPE, /** Package declaration */ PACKAGE, /** * Type parameter declaration * * @since 1.8 */ TYPE_PARAMETER, /** * Use of a type * * @since 1.8 */ TYPE_USE, /** * Module declaration. * * @since 9 */ MODULE }
@Retention(RetentionPolicy.RUNTIME)
public enum RetentionPolicy { /** * Annotations are to be discarded by the compiler. */ SOURCE, /** * Annotations are to be recorded in the class file by the compiler * but need not be retained by the VM at run time. This is the default * behavior. */ CLASS, /** * Annotations are to be recorded in the class file by the compiler and * retained by the VM at run time, so they may be read reflectively. * * @see java.lang.reflect.AnnotatedElement */ RUNTIME }
SOURCE 当编译时,注解将不会出现在class源文件中
CLASS 注解将会保留在class源文件中,但是不会被jvm加载,也就意味着不能通过反射去找到该注解,因为没有加载到java虚拟机中
RUNTIME是既会保留在源文件中,也会被虚拟机加载
@Documented
java doc 会生成注解信息
@Inherited
是否会被继承,就是如果一个子类继承了使用了该注解的类,那么子类也能继承该注解
@SpringBootConfiguration
标注在某个类上,表示这是一个Spring Boot的配置类,本质上也是使用了@Configuration注解
@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Configuration public @interface SpringBootConfiguration {
@EnableAutoConfiguration
@EnableAutoConfiguration告诉SpringBoot开启自动配置,会帮我们自动去加载 自动配置类
@Target({ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @AutoConfigurationPackage @Import({AutoConfigurationImportSelector.class}) public @interface EnableAutoConfiguration {
@AutoConfigurationPackage
将当前配置类所在包保存在BasePackages的Bean中。供Spring内部使用
@Import({AutoConfigurationImportSelector.class})来加载配置类
配置文件的位置:META-INF/spring.factories,该配置文件中定义了大量的配置类,当springboot启动时,会自动加载这些配置类,初始化Bean
并不是所有Bean都会被初始化,在配置类中使用Condition来加载满足条件的Bean
二、案例
自定义redis-starter,要求当导入redis坐标时,spirngboot自动创建jedis的Bean
步骤
1.创建redis-spring-boot-autoconfigure模块
2.创建redis-spring-boot-starter模块,依赖redis-spring-boot-autoconfigure的模块
3.在redis-spring-boot-autoconfigure模块中初始化jedis的bean,并定义META-INF/spring.factories文件
4.在测试模块中引入自定义的redis-starter依赖,测试获取jedis的bean,操作redis
1.首先新建两个模块
删除一些没有用的东西,和启动类否则会报错
2.redis-spring-boot-starter模块的pom.xml里面引入redis-spring-boot-autoconfigure的模块的坐标
3.RedisAutoConfiguration配置类
package com.blb; import org.springframework.boot.context.properties.EnableConfigurationProperties; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import redis.clients.jedis.Jedis; @Configuration @EnableConfigurationProperties(RedisProperties.class) public class RedisAutoConfiguration { // 提供Jedis的bean @Bean public Jedis jedis(RedisProperties redisProperties){ return new Jedis(redisProperties.getHost(),redisProperties.getPort()); } }
RedisProperties
package com.blb; import org.springframework.boot.context.properties.ConfigurationProperties; @ConfigurationProperties(prefix = "redis") public class RedisProperties { private String host="localhost"; private int port=6379; public String getHost() { return host; } public void setHost(String host) { this.host = host; } public int getPort() { return port; } public void setPort(int port) { this.port = port; } }
@ComponentScan
扫描包 相当于在spring.xml 配置中context:comonent-scan 但是并没有指定basepackage,如果没有指定spring底层会自动扫描当前配置类所有在的包
排除的类型
public enum FilterType { /** * Filter candidates marked with a given annotation. * @see org.springframework.core.type.filter.AnnotationTypeFilter */ ANNOTATION, /** * Filter candidates assignable to a given type. * @see org.springframework.core.type.filter.AssignableTypeFilter */ ASSIGNABLE_TYPE, /** * Filter candidates matching a given AspectJ type pattern expression. * @see org.springframework.core.type.filter.AspectJTypeFilter */ ASPECTJ, /** * Filter candidates matching a given regex pattern. * @see org.springframework.core.type.filter.RegexPatternTypeFilter */ REGEX, /** Filter candidates using a given custom * {@link org.springframework.core.type.filter.TypeFilter} implementation. */ CUSTOM }
ANNOTATION 默认根据注解的完整限定名设置排除
ASSIGNABLE_TYPE 根据类的完整限定名排除
ASPECTJ 根据切面表达式设置排除
REGEX 根据正则表达式设置排除
CUSTOM 自定义设置排除
@ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class), @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
按照自定义的方式来排除需要指定一个类,要实现TypeFilter接口,重写match方法
public class TypeExcludeFilter implements TypeFilter, BeanFactoryAware { public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException { if (this.beanFactory instanceof ListableBeanFactory && this.getClass() == TypeExcludeFilter.class) { Iterator var3 = this.getDelegates().iterator(); while(var3.hasNext()) { TypeExcludeFilter delegate = (TypeExcludeFilter)var3.next(); if (delegate.match(metadataReader, metadataReaderFactory)) { return true; } } } return false; } }
TypeExcludeFilter :springboot对外提供的扩展类, 可以供我们去按照我们的方式进行排除
AutoConfigurationExcludeFilter :排除所有配置类并且是自动配置类中里面的其中一个
示例
package com.blb.springbootyuanli.config; import org.springframework.boot.context.TypeExcludeFilter; import org.springframework.core.type.classreading.MetadataReader; import org.springframework.core.type.classreading.MetadataReaderFactory; import java.io.IOException; public class MyTypeExcludeFilter extends TypeExcludeFilter { @Override public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException { if(metadataReader.getClassMetadata().getClass()==UserConfig.class){ return true; } return false; } }
三、Condition
@Conditional是Spring4新提供的注解,它的作用是按照一定的条件进行判断,满足条件给容器注册bean,实现选择性的创建bean的操作,该注解为条件装配注解
源码
@Target({ElementType.TYPE, ElementType.METHOD}) @Retention(RetentionPolicy.RUNTIME) @Documented public @interface Conditional { /** * All {@link Condition} classes that must {@linkplain Condition#matches match} * in order for the component to be registered. */ Class<? extends Condition>[] value(); }
@FunctionalInterface public interface Condition { /** * Determine if the condition matches. * @param context the condition context * @param metadata the metadata of the {@link org.springframework.core.type.AnnotationMetadata class} * or {@link org.springframework.core.type.MethodMetadata method} being checked * @return {@code true} if the condition matches and the component can be registered, * or {@code false} to veto the annotated component's registration */ boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata); }
重写matches方法如果返回true spring则会帮你创建该对象,否则则不会
springboot提供的常用条件注解
@ConditionalOnProperty:判断文件中是否有对应属性和值才实例化Bean @ConditionalOnClass 检查类在加载器中是否存在对应的类,如果有则被注解修饰的类就有资格被 Spring 容器所注册,否则会被跳过。 @ConditionalOnBean 仅仅在当前上下文中存在某个对象时,才会实例化一个 Bean @ConditionalOnClass 某个 CLASS 位于类路径上,才会实例化一个 Bean @ConditionalOnExpression 当表达式为 true 的时候,才会实例化一个 Bean @ConditionalOnMissingBean 仅仅在当前上下文中不存在某个对象时,才会实例化一个 Bean @ConditionalOnMissingClass 某个 CLASS 类路径上不存在的时候,才会实例化一个 Bean
案例
在springIOC容器中有一个User的bean,现要求:
引入jedis坐标后,加载该bean,没导入则不加载
实体类
package com.blb.springbootyuanli.entity; public class User { private String name; private int age; get/set
UserConfig
配置类
package com.blb.springbootyuanli.config; import com.blb.springbootyuanli.condition.UserCondition; import com.blb.springbootyuanli.entity.User; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Conditional; import org.springframework.context.annotation.Configuration; @Configuration public class UserConfig { @Bean @Conditional(UserCondition.class) public User user(){ return new User(); } }
UserCondition
实现Condition接口,重写matches方法
package com.blb.springbootyuanli.condition; import org.springframework.context.annotation.Condition; import org.springframework.context.annotation.ConditionContext; import org.springframework.core.type.AnnotatedTypeMetadata; public class UserCondition implements Condition { @Override public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) { //思路判断jedis的class文件是否存在 boolean flag=true; try { Class<?> aClass = Class.forName("redis.clients.jedis.Jedis"); } catch (ClassNotFoundException e) { flag=false; } return flag; } }
启动类
package com.blb.springbootyuanli; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.context.ConfigurableApplicationContext; @SpringBootApplication public class SpringbootYuanliApplication { public static void main(String[] args) { ConfigurableApplicationContext app = SpringApplication.run(SpringbootYuanliApplication.class, args); Object user = app.getBean("user"); System.out.println(user); } }
当我们在pom.xml引入jedis的坐标时,就可以打印user对象,当删除jedis的坐标时,运行就会报错 No bean named ‘user' available
四、案例升级
将类的判断定义为动态的,判断那个字节码文件可以动态指定
自定义一个注解
添加上元注解
package com.blb.springbootyuanli.condition; import org.springframework.context.annotation.Conditional; import java.lang.annotation.*; @Target({ElementType.TYPE, ElementType.METHOD}) //该注解的添加范围 @Retention(RetentionPolicy.RUNTIME) //该注解的生效时机 @Documented //生成javadoc的文档 @Conditional(UserCondition.class) public @interface UserClassCondition { String[] value(); }
UserConfig
package com.blb.springbootyuanli.config; import com.blb.springbootyuanli.condition.UserClassCondition; import com.blb.springbootyuanli.entity.User; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class UserConfig { @Bean //@Conditional(UserCondition.class) @UserClassCondition("redis.clients.jedis.Jedis") public User user(){ return new User(); } }
package com.blb.springbootyuanli.condition; import org.springframework.context.annotation.Condition; import org.springframework.context.annotation.ConditionContext; import org.springframework.core.type.AnnotatedTypeMetadata; import java.util.Map; public class UserCondition implements Condition { /** * * @param context 上下文对象,用于获取环境,ioc容器,classloader对象 * @param metadata 注解元对象。可以获取注解定义的属性值 * @return */ @Override public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) { //思路判断指定属性的class文件是否存在 //获取注解属性值 value Map<String,Object> map=metadata.getAnnotationAttributes(UserClassCondition.class.getName()); String[] values= (String[])map.get("value"); boolean flag=true; try { for(String classname:values){ Class<?> aClass = Class.forName(classname); } } catch (ClassNotFoundException e) { flag=false; } return flag; } }
测试自带的注解
package com.blb.springbootyuanli.config; import com.blb.springbootyuanli.entity.User; import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class UserConfig { @Bean //@Conditional(UserCondition.class) //@UserClassCondition("redis.clients.jedis.Jedis") @ConditionalOnProperty(name="age",havingValue = "18") //只有在配置文件中有age并且值为18spring在能注册该bean public User user(){ return new User(); } }
五、小结
自定义条件:
1.定义条件类:自定义类实现Condition接口,重写重写matches方法,在matches方法中进行逻辑判断,返回boolean值
2.matches方法的两个参数:
context:上下文对象,可以获取属性值,获取类加载器,获取BeanFactory
metadata:元数据对象,用于获取注解属性
3.判断条件:在初始化Bean时,使用@Conditional(条件类.class) 注解
加载全部内容