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spring初始化执行顺序原理

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Spring中初始化方法的执行顺序

首先通过一个例子来看其顺序

/**
 * 调用顺序 init2(PostConstruct注解) --> afterPropertiesSet(InitializingBean接口) --> init3(init-method配置)
 */
public class Test implements InitializingBean {
    public void init3(){
        System.out.println("init3");
    }
    @PostConstruct
    public void init2(){
        System.out.println("init2");
    }
    @Override
    public void afterPropertiesSet() throws Exception {
        System.out.println("afterPropertiesSet");
    }
}

配置

<context:annotation-config/>
<bean class="com.cyy.spring.lifecycle.Test" id="test" init-method="init3"/>

通过运行,我们得出其执行顺序为init2(PostConstruct注解) --> afterPropertiesSet(InitializingBean接口) --> init3(init-method配置)。但是为什么是这个顺序呢?我们可以通过分析其源码得出结论。

首先在解析配置文件的时候,碰到context:annotation-config/自定义标签会调用其自定义解析器,这个自定义解析器在哪儿呢?在spring-context的spring.handlers中有配置

http\://www.springframework.org/schema/context=org.springframework.context.config.ContextNamespaceHandler

我们进入这个类看

public class ContextNamespaceHandler extends NamespaceHandlerSupport {
    @Override
    public void init() {
        registerBeanDefinitionParser("property-placeholder", new PropertyPlaceholderBeanDefinitionParser());
        registerBeanDefinitionParser("property-override", new PropertyOverrideBeanDefinitionParser());
        registerBeanDefinitionParser("annotation-config", new AnnotationConfigBeanDefinitionParser());
        registerBeanDefinitionParser("component-scan", new ComponentScanBeanDefinitionParser());
        registerBeanDefinitionParser("load-time-weaver", new LoadTimeWeaverBeanDefinitionParser());
        registerBeanDefinitionParser("spring-configured", new SpringConfiguredBeanDefinitionParser());
        registerBeanDefinitionParser("mbean-export", new MBeanExportBeanDefinitionParser());
        registerBeanDefinitionParser("mbean-server", new MBeanServerBeanDefinitionParser());
    }
}

我们看到了annotation-config了

我们只关心这个标签,那我们就进入AnnotationConfigBeanDefinitionParser类中,看它的parse方法

public BeanDefinition parse(Element element, ParserContext parserContext) {
    Object source = parserContext.extractSource(element);
    // Obtain bean definitions for all relevant BeanPostProcessors.
    Set<BeanDefinitionHolder> processorDefinitions =
            AnnotationConfigUtils.registerAnnotationConfigProcessors(parserContext.getRegistry(), source);
    // Register component for the surrounding <context:annotation-config> element.
    CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), source);
    parserContext.pushContainingComponent(compDefinition);
    // Nest the concrete beans in the surrounding component.
    for (BeanDefinitionHolder processorDefinition : processorDefinitions) {
        parserContext.registerComponent(new BeanComponentDefinition(processorDefinition));
    }
    // Finally register the composite component.
    parserContext.popAndRegisterContainingComponent();
    return null;
}

我们重点看下这行代码

Set<BeanDefinitionHolder> processorDefinitions = AnnotationConfigUtils.registerAnnotationConfigProcessors(parserContext.getRegistry(), source);

我们追踪进去(其中省略了一些我们不关心的代码)

public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
        BeanDefinitionRegistry registry, Object source) {
    ...
    // Check for JSR-250 support, and if present add the CommonAnnotationBeanPostProcessor.
    if (jsr250Present && !registry.containsBeanDefinition(COMMON_ANNOTATION_PROCESSOR_BEAN_NAME)) {
        RootBeanDefinition def = new RootBeanDefinition(CommonAnnotationBeanPostProcessor.class);
        def.setSource(source);
        beanDefs.add(registerPostProcessor(registry, def, COMMON_ANNOTATION_PROCESSOR_BEAN_NAME));
    }
    ...
}

在这个方法其中注册了一个CommonAnnotationBeanPostProcessor类,这个类是我们@PostConstruct这个注解发挥作用的基础。

在bean实例化的过程中,会调用AbstractAutowireCapableBeanFactory类的doCreateBean方法,在这个方法中会有一个调用initializeBean方法的地方,

我们直接看initializeBean这个方法

protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd) {
    if (System.getSecurityManager() != null) {
        AccessController.doPrivileged(new PrivilegedAction<Object>() {
            @Override
            public Object run() {
                invokeAwareMethods(beanName, bean);
                return null;
            }
        }, getAccessControlContext());
    }
    else {
        invokeAwareMethods(beanName, bean);
    }
    Object wrappedBean = bean;
    if (mbd == null || !mbd.isSynthetic()) {
        // 调用@PostConstruct方法注解的地方
        wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);//①
    }
    try {
        // 调用afterPropertiesSet和init-method地方
        invokeInitMethods(beanName, wrappedBean, mbd);// ②
    }
    catch (Throwable ex) {
        throw new BeanCreationException(
                (mbd != null ? mbd.getResourceDescription() : null),
                beanName, "Invocation of init method failed", ex);
    }
    if (mbd == null || !mbd.isSynthetic()) {
        wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);
    }
    return wrappedBean;
}

先看①这行,进入applyBeanPostProcessorsBeforeInitialization方法

public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
        throws BeansException {
    Object result = existingBean;
    for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
        result = beanProcessor.postProcessBeforeInitialization(result, beanName);
        if (result == null) {
            return result;
        }
    }
    return result;
}

我们还记得前面注册的一个类CommonAnnotationBeanPostProcessor,其中这个类间接的实现了BeanPostProcessor接口,所以此处会调用CommonAnnotationBeanPostProcessor类的postProcessBeforeInitialization方法,它本身并没有实现这个方法,但他的父类InitDestroyAnnotationBeanPostProcessor实现了postProcessBeforeInitialization的方法,其中这个方法就实现调用目标类上有@PostConstruct注解的方法

// 获取目标类上有@PostConstruct注解的方法并调用
public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    LifecycleMetadata metadata = findLifecycleMetadata(bean.getClass());
    try {
        metadata.invokeInitMethods(bean, beanName);
    }
    catch (InvocationTargetException ex) {
        throw new BeanCreationException(beanName, "Invocation of init method failed", ex.getTargetException());
    }
    catch (Throwable ex) {
        throw new BeanCreationException(beanName, "Failed to invoke init method", ex);
    }
    return bean;
}

然后接着看initializeBean方法中②这一行代码,首先判断目标类有没有实现InitializingBean,如果实现了就调用目标类的afterPropertiesSet方法,然后如果有配置init-method就调用其方法

protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd)
        throws Throwable {
    // 1、调用afterPropertiesSet方法
    boolean isInitializingBean = (bean instanceof InitializingBean);
    if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod("afterPropertiesSet"))) {
        if (logger.isDebugEnabled()) {
            logger.debug("Invoking afterPropertiesSet() on bean with name '" + beanName + "'");
        }
        if (System.getSecurityManager() != null) {
            try {
                AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
                    @Override
                    public Object run() throws Exception {
                        ((InitializingBean) bean).afterPropertiesSet();
                        return null;
                    }
                }, getAccessControlContext());
            }
            catch (PrivilegedActionException pae) {
                throw pae.getException();
            }
        }
        else {
            ((InitializingBean) bean).afterPropertiesSet();
        }
    }
    // 2、调用init-method方法
    if (mbd != null) {
        String initMethodName = mbd.getInitMethodName();
        if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&
                !mbd.isExternallyManagedInitMethod(initMethodName)) {
            invokeCustomInitMethod(beanName, bean, mbd);
        }
    }
}

至此Spring的初始化方法调用顺序的解析就已经完了。 

spring加载顺序典例

借用log4j2,向数据库中新增一条记录,对于特殊的字段需要借助线程的环境变量。其中某个字段需要在数据库中查询到具体信息后插入,在借助Spring MVC的Dao层时遇到了加载顺序问题。

解决方案

log4j2插入数据库的方案参考文章:

<Column name="user_info" pattern="%X{user_info}" isUnicode="false" />

需要执行日志插入操作(比如绑定到一个级别为insert、logger.insert())的线程中有环境变量user_info。

解决环境变量的方法:

拦截器: 

@Component
public class LogInterceptor implements HandlerInterceptor {
    /**
     * 需要记录在log中的参数
     */
    public static final String USER_INFO= "user_info";
    @Override
    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object arg)
        throws Exception {
        String userName = LoginContext.getCurrentUsername();
        ThreadContext.put(USER_INFO, getUserInfo());
    }
    
    @Override
    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse,
        Object arg, Exception exception) throws Exception {
        ThreadContext.remove(USER_INFO);
    }

需要拦截的URL配置:

@Configuration
public class LogConfigurer implements WebMvcConfigurer {
    String[] logUrl = new String[] {
        "/**",
    };
    String[] excludeUrl = new String[] {
        "/**/*.js", "/**/*.css", "/**/*.jpg", "/**/*.png", "/**/*.svg", "/**/*.woff", "/**/*.eot", "/**/*.ttf",
        "/**/*.less", "/favicon.ico", "/license/lackofresource", "/error"
    };
    /**
     * 注册一个拦截器
     *
     * @return HpcLogInterceptor
     */
    @Bean
    public LogInterceptor setLogBean() {
        return new LogInterceptor();
    }
    @Override
    public void addInterceptors(InterceptorRegistry reg) {
        // 拦截的对象会进入这个类中进行判断
        InterceptorRegistration registration = reg.addInterceptor(setLogBean());
        // 添加要拦截的路径与不用拦截的路径
        registration.addPathPatterns(logUrl).excludePathPatterns(excludeUrl);
    }
}

如下待优化:

问题就出在如何获取信息这个步骤,原本的方案是:

通过Dao userDao从数据库查询信息,然后填充进去。

出现的问题是:userDao无法通过@Autowired方式注入。

原因:

调用处SpringBoot未完成初始化,导致dao层在调用时每次都是null。

因此最后采用的方式如下: 

@Component
public class LogInterceptor implements HandlerInterceptor {
    /**
     * 需要记录在log中的参数
     */
    public static final String USER_INFO= "user_info";
	
	@Resource(name = "jdbcTemplate")
    private JdbcTemplate jdbcTemplate;
    @Override
    public boolean preHandle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, Object arg)
        throws Exception {
        String userName = LoginContext.getCurrentUsername();
        ThreadContext.put(USER_INFO, getUserInfo());
    }
    
    @Override
    public void afterCompletion(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse,
        Object arg, Exception exception) throws Exception {
        ThreadContext.remove(USER_INFO);
    }
	public String getUserInfo(String userName) {
        String sqlTemplate = "select user_info from Test.test_user where user_name = ?";
        List<String> userInfo= new ArrayList<>();
        userInfo= jdbcTemplate.query(sqlTemplate, preparedStatement -> {
            preparedStatement.setString(1, userName);
        }, new SecurityRoleDtoMapper());
        if (userInfo.size() == 0) {
            return Constants.HPC_NORMAL_USER;
        }
        return userInfo.get(0);
    }

以上为个人经验,希望能给大家一个参考,也希望大家多多支持。 

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