【深入浅出Spring原理及实战】「源码原理实战」从底层角度去分析研究PropertySourcesPlaceholderConfigurer的原理及实战注入机

<bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource"  init-method="init" destroy-method="close">
    <property name="url" value="${jdbc.url}"/>
    <property name="username" value="${jdbc.username}"/>
    <property name="password" value="${jdbc.password}"/>
</bean>
复制代码

@Value("${config}")
private String config;
复制代码

@Configuration
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
public class PropertyPlaceholderAutoConfiguration {
  @Bean
  @ConditionalOnMissingBean(search = SearchStrategy.CURRENT)
  public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
    return new PropertySourcesPlaceholderConfigurer();
  }
}
复制代码

@Override
  public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
    if (this.propertySources == null) {
      this.propertySources = new MutablePropertySources();
      if (this.environment != null) {
        this.propertySources.addLast(
          new PropertySource<Environment>(ENVIRONMENT_PROPERTIES_PROPERTY_SOURCE_NAME, 
            this.environment) {
            @Override
            @Nullable
            public String getProperty(String key) {
              return this.source.getProperty(key);
            }
          }
        );
      }
      try {
        PropertySource<?> localPropertySource =
            new PropertiesPropertySource(LOCAL_PROPERTIES_PROPERTY_SOURCE_NAME, mergeProperties());
        if (this.localOverride) {
          this.propertySources.addFirst(localPropertySource);
        }
        else {
          this.propertySources.addLast(localPropertySource);
        }
      }
      catch (IOException ex) {
        throw new BeanInitializationException("Could not load properties", ex);
      }
    }
    processProperties(beanFactory, new PropertySourcesPropertyResolver(this.propertySources));
    this.appliedPropertySources = this.propertySources;
  }
复制代码

/**
   * Visit each bean definition in the given bean factory and attempt to replace ${...} property
   * placeholders with values from the given properties.
   */
  protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess,
      final ConfigurablePropertyResolver propertyResolver) throws BeansException {
       // 设置属性值解析器所使用的占位符格式参数，缺省为:
       // 占位符前缀 ${
    propertyResolver.setPlaceholderPrefix(this.placeholderPrefix);
       // 占位符后缀 }
    propertyResolver.setPlaceholderSuffix(this.placeholderSuffix);
       // 缺省值分隔符 :
    propertyResolver.setValueSeparator(this.valueSeparator);
       // 结合属性 this. ignoreUnresolvablePlaceholders对propertyResolver 作进一步封装，
       // 封装出来一个 StringValueResolver valueResolver,这是最终要应用的属性值解析器
    StringValueResolver valueResolver = strVal -> {
      String resolved = (this.ignoreUnresolvablePlaceholders ?
          propertyResolver.resolvePlaceholders(strVal) :
          propertyResolver.resolveRequiredPlaceholders(strVal));
      if (this.trimValues) {
        resolved = resolved.trim();
      }
      return (resolved.equals(this.nullValue) ? null : resolved);
    };
       // 调用基类PlaceholderConfigurerSupport实现的对容器中所有 bean定义进行遍历处理属性值中占位符解析的逻辑
    doProcessProperties(beanFactoryToProcess, valueResolver);
  }
复制代码

protected void doProcessProperties(ConfigurableListableBeanFactory beanFactoryToProcess,
            StringValueResolver valueResolver) {
        // ignore
        ....
        // New in Spring 2.5: resolve placeholders in alias target names and aliases as well.
        beanFactoryToProcess.resolveAliases(valueResolver);
        // New in Spring 3.0: resolve placeholders in embedded values such as annotation attributes.
        beanFactoryToProcess.addEmbeddedValueResolver(valueResolver);
    }
复制代码

// 获取注解的 value() 值。被写死为 Class<? extends Annotation> valueAnnotationType = Value.class;
// 见类 QualifierAnnotationAutowireCandidateResolver
Object value = getAutowireCandidateResolver().getSuggestedValue(descriptor);
if (value != null) {
    if (value instanceof String) {
        // 通过PropertySourcesPlaceholderConfigurer写入的键值对元素获取元素的值.
        // 方法内注册了多个StringValueResolver，循环查找值。提供者为PropertySourcesPlaceholderConfigurer,因此配置多个解析器的时候是以最后的配置为准的。
        String strVal = resolveEmbeddedValue((String) value);
        BeanDefinition bd = (beanName != null && containsBean(beanName) ? getMergedBeanDefinition(beanName) : null);
        value = evaluateBeanDefinitionString(strVal, bd);
    }
    TypeConverter converter = (typeConverter != null ? typeConverter : getTypeConverter());
    return (descriptor.getField() != null ?
            converter.convertIfNecessary(value, type, descriptor.getField()) :
            converter.convertIfNecessary(value, type, descriptor.getMethodParameter()));
}
复制代码

<bean id="propertyConfigurer"class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
   <property name="location">
     <value>conf/sqlmap/jdbc.properties</value>
   </property>
    <property name="fileEncoding">
      <value>UTF-8</value>
    </property>
</bean>
复制代码

<bean id="propertyConfigurer"class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">  
    <property name="locations">
        <list>
            <value>/WEB-INF/mail.properties</value>  
            <value>classpath: conf/sqlmap/jdbc.properties</value>
     </list>
    </property>
</bean>
复制代码

<context:property-placeholder location="classpath*:/WEB-INF/mail.properties" />
复制代码

@PropertySource(value = "classpath:config/application-config.properties")
复制代码

@PropertySource(value = {"classpath:config/application-config1.properties","classpath:config/application-config2.properties"})
复制代码

@Configuration
@ComponentScan(basePackages = "com.libo.config")
@PropertySource(value = "classpath:config/application-config.properties")
public class TestPropertieEnvironment { 
    @Autowired
    Environment environment;
    public String properties(){
        String key = this.environment.getProperty("config.key");
        System.out.println(key);
        return null;
    }
}
复制代码

config.key=1
config.value=2
复制代码

public class Test {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(TestPropertieEnvironment.class);
        ServiceConfiguration hc2 = (TestPropertieEnvironment) context.getBean("testPropertieEnvironment");
        hc2.properties();
    }
}
复制代码

@Component
@PropertySource(value = "classpath:config/application-config.properties")
public class PropertiesConfig {
    @Value("${config.value}")
    private String value;
    @Value("${config.key}")
    private String key;
}
复制代码

@Configuration
@ComponentScan(basePackages = "com.libo.config")
public class PropertiesConfiguration2 { 
    @Bean 
    public static PropertyPlaceholderConfigurer configurer() { 
         PropertyPlaceholderConfigurer ppc = new PropertyPlaceholderConfigurer();
         Resource resources = new ClassPathResource( "config/appplication-config.properties" );
         ppc.setLocation(resources);
         return ppc; 
    } 
    @Bean
    public Configs2 configs2(@Value("${ds.user}") String user, @Value("${key1}") String key1) {
        Configs2 configs = new Configs2();
        configs.setApiKeyId(user);
        configs.setSecretApiKey(key1);
        System.out.println("in ServiceConfiguration" + configs);
        return configs;
    }
}
@Service
public class TestConfigs2 {
    @Autowired
    Configs2 configs2;
    @Autowired
    Configs configs;
    public void testConfigs2() {
        System.out.println("configs:"+configs.getApiKeyId());
        System.out.println("configs2:"+configs2.getApiKeyId());
    }
}
复制代码

import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;
public class Test {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(ServiceConfiguration2.class);       
        TestConfigs2 hc2 = (TestConfigs2) context.getBean("testConfigs2");
        hc2.testConfigs2();
    }
}
复制代码

@PropertySources({
//@PropertySource("classpath:db.properties"),
@PropertySource(value="classpath:db.properties", ignoreResourceNotFound=true),
@PropertySource("classpath:spring/config.properties")
  public class AppConfig {
    @Value("${key1}")
    private String key1;
    @Value("${key2}")
    private String key2;
    @Override
    public String toString() {
        return "AppConfig [key1=" + key1 + ", key2=" + key2 + "]";
    } 
}