SSM系列(二)---Spring 常用注解分析

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<context:annotation-config>

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public class Student {
    @Value(value = "illusory")
    private String name;
    @Value(value = "23")
    private int age;
    @Autowired
    private Book book;
}
public class Book {
    @Value(value = "defaultType")
    private String type;
    @Value(value = "defaultName")
    private String name;
}

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<property name="name" value="illusory"></property>

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<property name="book" ref="book"></property>

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  <bean id="student" class="spring.Student"></bean>
  <bean id="book" class="spring.Book"></bean>
   <context:annotation-config />

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@Component(value = "student")
public class Student {
    @Value(value = "illusory")
    private String name;
    @Value(value = "23")
    private int age;
    @Autowired
    private Book book;
}

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<context:component-scan base-package="spring"/>

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    @PostConstruct
    public void init() {
        System.out.println("init");
    }

    @PreDestroy
    public void destory() {
        System.out.println("destory");
    }

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@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component  //看这里！！！
public @interface Configuration {
    String value() default "";

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@Configuration
public class AppConfig {
    @Bean
    public MyService myService() {
        return new MyServiceImpl();
    }
}

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<beans>
    <bean id="myService" class="com.acme.services.MyServiceImpl"/>
</beans>

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@Configuration
public static class Config {

    @Bean
    public SimpleBean simpleBean() {
        return new SimpleBean();
    }

    @Bean
    public SimpleBeanConsumer simpleBeanConsumer() {
        return new SimpleBeanConsumer(simpleBean());
    }
}

@Component
public static class Config {

    @Bean
    public SimpleBean simpleBean() {
        return new SimpleBean();
    }

    @Bean
    public SimpleBeanConsumer simpleBeanConsumer() {
        return new SimpleBeanConsumer(simpleBean());
    }
}

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public void enhanceConfigurationClasses(ConfigurableListableBeanFactory beanFactory) {
        Map<String, AbstractBeanDefinition> configBeanDefs = new LinkedHashMap<String, AbstractBeanDefinition>();
        for (String beanName : beanFactory.getBeanDefinitionNames()) {
            BeanDefinition beanDef = beanFactory.getBeanDefinition(beanName);
            //判断是否被@Configuration标注
            if (ConfigurationClassUtils.isFullConfigurationClass(beanDef)) {
                if (!(beanDef instanceof AbstractBeanDefinition)) {
                    throw new BeanDefinitionStoreException("Cannot enhance @Configuration bean definition '" +
                            beanName + "' since it is not stored in an AbstractBeanDefinition subclass");
                }
                else if (logger.isWarnEnabled() && beanFactory.containsSingleton(beanName)) {
                    logger.warn("Cannot enhance @Configuration bean definition '" + beanName +
                            "' since its singleton instance has been created too early. The typical cause " +
                            "is a non-static @Bean method with a BeanDefinitionRegistryPostProcessor " +
                            "return type: Consider declaring such methods as 'static'.");
                }
                configBeanDefs.put(beanName, (AbstractBeanDefinition) beanDef);
            }
        }
        if (configBeanDefs.isEmpty()) {
            // nothing to enhance -> return immediately
            return;
        }
        ConfigurationClassEnhancer enhancer = new ConfigurationClassEnhancer();
        for (Map.Entry<String, AbstractBeanDefinition> entry : configBeanDefs.entrySet()) {
            AbstractBeanDefinition beanDef = entry.getValue();
            // If a @Configuration class gets proxied, always proxy the target class
            beanDef.setAttribute(AutoProxyUtils.PRESERVE_TARGET_CLASS_ATTRIBUTE, Boolean.TRUE);
            try {
                // Set enhanced subclass of the user-specified bean class
                Class<?> configClass = beanDef.resolveBeanClass(this.beanClassLoader);
                //生成代理的class
                Class<?> enhancedClass = enhancer.enhance(configClass, this.beanClassLoader);
                if (configClass != enhancedClass) {
                    if (logger.isDebugEnabled()) {
                        logger.debug(String.format("Replacing bean definition '%s' existing class '%s' with " +
                                "enhanced class '%s'", entry.getKey(), configClass.getName(), enhancedClass.getName()));
                    }
                    //替换class，将原来的替换为CGLIB代理的class
                    beanDef.setBeanClass(enhancedClass);
                }
            }
            catch (Throwable ex) {
                throw new IllegalStateException("Cannot load configuration class: " + beanDef.getBeanClassName(), ex);
            }
        }
    }

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//是否为配置类
public static boolean isConfigurationCandidate(AnnotationMetadata metadata) {
return (isFullConfigurationCandidate(metadata) || isLiteConfigurationCandidate(metadata));
}

//是否为完整配置类
public static boolean isFullConfigurationCandidate(AnnotationMetadata metadata) {
return metadata.isAnnotated(Configuration.class.getName());
}
//是否为精简配置类
public static boolean isLiteConfigurationCandidate(AnnotationMetadata metadata) {
    // Do not consider an interface or an annotation...
    if (metadata.isInterface()) {
        return false;
    }

    // Any of the typical annotations found?
    for (String indicator : candidateIndicators) {
        if (metadata.isAnnotated(indicator)) {
            return true;
        }
    }

    // Finally, let's look for @Bean methods...
    try {
        return metadata.hasAnnotatedMethods(Bean.class.getName());
    }
    catch (Throwable ex) {
        if (logger.isDebugEnabled()) {
            logger.debug("Failed to introspect @Bean methods on class [" + metadata.getClassName() + "]: " + ex);
        }
        return false;
    }
}
//精简配置类包含的注解
static {
    candidateIndicators.add(Component.class.getName());
    candidateIndicators.add(ComponentScan.class.getName());
    candidateIndicators.add(Import.class.getName());
    candidateIndicators.add(ImportResource.class.getName());
}