Spring 配置解析之Properties

http://www.cnblogs.com/dragonfei/archive/2016/10/09/5906474.html

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1.简单示例：

SpringBoot中的的配置简单属性类支持ConfigurationProperties方式，看一个简单的示例。

 1 @ConfigurationProperties(prefix = "org.dragonfei.demo")
 2 public class DemoProperties {
 3     private String name;
 4     private String password;
 5     private String test;
 6
 7     public String getName() {
 8         return name;
 9     }
10
11     public void setName(String name) {
12         this.name = name;
13     }
14
15     public String getPassword() {
16         return password;
17     }
18
19     public void setPassword(String password) {
20         this.password = password;
21     }
22
23     public String getTest() {
24         return test;
25     }
26
27     public void setTest(String test) {
28         this.test = test;
29     }
30
31     @Override
32     public String toString() {
33         return "DemoProperties{" +
34                 "name='" + name + '\'' +
35                 ", password='" + password + '\'' +
36                 ", test='" + test + '\'' +
37                 '}';
38     }
39 }

1 org.dragonfei.demo.name=dragonfei
2 org.dragonfei.demo.password=password
3 org.dragonfei.demo.test=test

1 @Configuration
2 @EnableConfigurationProperties({DemoProperties.class})
3 public class DemoConfiguration {
4 }

 1 @RunWith(SpringJUnit4ClassRunner.class)
 2 @SpringApplicationConfiguration(classes = DemoConfiguration.class)
 3 @EnableAutoConfiguration
 4 public class DemoPropertiesTest {
 5
 6     @Autowired
 7     private DemoProperties properties;
 8     @Test
 9     public void testProperties(){
10         System.out.println(properties.toString());
11     }
12 }

1 DemoProperties{name='dragonfei', password='password', test='test'}

DemoProperties神奇的注入到Spring容器中了。有没有跟我一样很兴奋，这样的 一大好处，将配置文件的属性以类的形式展现，在需要使用的时候只需要，autowire需要的类就可以了，避免大片重复的的${a.b.c}

 2.Properties属性自动装配实现

DemoProperties这么神奇注入到容器中，天下没有什么是莫名奇妙的，引出了两个关键问题：

• DemoProperties是怎样注入到容器中？
• DemoProperties中的各个属性是怎么被赋值的呢？

　　要回答上面的问题，必须对@Configuration如何注入bean做一个简单的回顾：

• 在解析@Congiguraion的时候，会调用@Import中引入的类
• 如果@Import中是ImportBeanDefinitionegistar的子类，会直接调用registerBeanDefinitions
• 如果@Import中是ImportSelector类型，会调用selectImports（）返回的bean的registerBeanDefinitions方法。
• registerBeanDefinitions方法会向BeanFactory中添加新的bean。

回到正题。打开EnableConfigurationProperties

 1 @Target(ElementType.TYPE)
 2 @Retention(RetentionPolicy.RUNTIME)
 3 @Documented
 4 @Import(EnableConfigurationPropertiesImportSelector.class)
 5 public @interface EnableConfigurationProperties {
 6
 7     /**
 8      * Convenient way to quickly register {@link ConfigurationProperties} annotated beans
 9      * with Spring. Standard Spring Beans will also be scanned regardless of this value.
10      * @return {@link ConfigurationProperties} annotated beans to register
11      */
12     Class<?>[] value() default {};
13
14 }

注意@Imoport里面的类

 1     public String[] selectImports(AnnotationMetadata metadata) {
 2         MultiValueMap<String, Object> attributes = metadata.getAllAnnotationAttributes(
 3                 EnableConfigurationProperties.class.getName(), false);
 4         Object[] type = attributes == null ? null
 5                 : (Object[]) attributes.getFirst("value");
 6         if (type == null || type.length == 0) {
 7             return new String[] {
 8                     ConfigurationPropertiesBindingPostProcessorRegistrar.class
 9                             .getName() };
10         }
11         return new String[] { ConfigurationPropertiesBeanRegistrar.class.getName(),
12                 ConfigurationPropertiesBindingPostProcessorRegistrar.class.getName() };
13     }

然后，会调用ConfigurationPropertiesBeanRegistar和ConfigurationPropertiesBindingPostProcessorRegistar的registerBeanDefinitions方法，前者是为了注入配置properties类，后者为属性绑定值

 1     @Override
 2         public void registerBeanDefinitions(AnnotationMetadata metadata,
 3                 BeanDefinitionRegistry registry) {
 4             MultiValueMap<String, Object> attributes = metadata
 5                     .getAllAnnotationAttributes(
 6                             EnableConfigurationProperties.class.getName(), false);
 7             List<Class<?>> types = collectClasses(attributes.get("value"));
 8             for (Class<?> type : types) {
 9                 String prefix = extractPrefix(type);
10                 String name = (StringUtils.hasText(prefix) ? prefix + "-" + type.getName()
11                         : type.getName());
12                 if (!registry.containsBeanDefinition(name)) {
13                     registerBeanDefinition(registry, type, name);
14                 }
15             }
16         }

 1     public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata,
 2             BeanDefinitionRegistry registry) {
 3         if (!registry.containsBeanDefinition(BINDER_BEAN_NAME)) {
 4             BeanDefinitionBuilder meta = BeanDefinitionBuilder
 5                     .genericBeanDefinition(ConfigurationBeanFactoryMetaData.class);
 6             BeanDefinitionBuilder bean = BeanDefinitionBuilder.genericBeanDefinition(
 7                     ConfigurationPropertiesBindingPostProcessor.class);
 8             bean.addPropertyReference("beanMetaDataStore", METADATA_BEAN_NAME);
 9             registry.registerBeanDefinition(BINDER_BEAN_NAME, bean.getBeanDefinition());
10             registry.registerBeanDefinition(METADATA_BEAN_NAME, meta.getBeanDefinition());
11         }
12     }

注意这里注入了ConfigurationPropertiesBindingPostProcessor，这才是属性赋值的关键。查看类图

注意到ConfigurationPropertiesBindingPostProcessor继承自BeanPostProcessor,他会在bean初始化前后调用before和after后置处理，这里，在Properties属性初始化完成后，会对绑定属性，

 1 private void postProcessBeforeInitialization(Object bean, String beanName,
 2             ConfigurationProperties annotation) {
 3         Object target = bean;
 4         PropertiesConfigurationFactory<Object> factory = new PropertiesConfigurationFactory<Object>(
 5                 target);
 6         if (annotation != null && annotation.locations().length != 0) {
 7             factory.setPropertySources(
 8                     loadPropertySources(annotation.locations(), annotation.merge()));
 9         }
10         else {
11             factory.setPropertySources(this.propertySources);
12         }
13         factory.setValidator(determineValidator(bean));
14         // If no explicit conversion service is provided we add one so that (at least)
15         // comma-separated arrays of convertibles can be bound automatically
16         factory.setConversionService(this.conversionService == null
17                 ? getDefaultConversionService() : this.conversionService);
18         if (annotation != null) {
19             factory.setIgnoreInvalidFields(annotation.ignoreInvalidFields());
20             factory.setIgnoreUnknownFields(annotation.ignoreUnknownFields());
21             factory.setExceptionIfInvalid(annotation.exceptionIfInvalid());
22             factory.setIgnoreNestedProperties(annotation.ignoreNestedProperties());
23             if (StringUtils.hasLength(annotation.prefix())) {
24                 factory.setTargetName(annotation.prefix());
25             }
26         }
27         try {
28             factory.bindPropertiesToTarget();
29         }
30         catch (Exception ex) {
31             String targetClass = ClassUtils.getShortName(target.getClass());
32             throw new BeanCreationException(beanName, "Could not bind properties to "
33                     + targetClass + " (" + getAnnotationDetails(annotation) + ")", ex);
34         }
35     }

至于真实的数据绑定，会从propertySources中获取，敬请期待....Spring 的数据绑定，这简单提一下关键的地方：

1 Set<String> names = getNames(relaxedTargetNames);
2         PropertyValues propertyValues = getPropertyValues(names, relaxedTargetNames);

请注意getNames，是获取prefix+属性构成的key值，prefix_property和prefix.property都会获取到

 1     private Set<String> getNames(Iterable<String> prefixes) {
 2         Set<String> names = new LinkedHashSet<String>();
 3         if (this.target != null) {
 4             PropertyDescriptor[] descriptors = BeanUtils
 5                     .getPropertyDescriptors(this.target.getClass());
 6             for (PropertyDescriptor descriptor : descriptors) {
 7                 String name = descriptor.getName();
 8                 if (!name.equals("class")) {
 9                     RelaxedNames relaxedNames = RelaxedNames.forCamelCase(name);
10                     if (prefixes == null) {
11                         for (String relaxedName : relaxedNames) {
12                             names.add(relaxedName);
13                         }
14                     }
15                     else {
16                         for (String prefix : prefixes) {
17                             for (String relaxedName : relaxedNames) {
18                                 names.add(prefix + "." + relaxedName);
19                                 names.add(prefix + "_" + relaxedName);
20                             }
21                         }
22                     }
23                 }
24             }
25         }
26         return names;
27     }

getPropertyValues会获取到满足上述条件的propertyValues,最后调用spring框架提供数据绑定策略进行数据绑定。

没有智能的代码，源码面前了无秘密