分析

SPRING通过

1.property-placeholder spring3.1以前实现是PropertyPlaceholderConfigurer，3.1以后是PropertySourcesPlaceholderConfigurer

<context:property-placeholder local-override="true" properties-ref="dataSourceProperties"
 file-encoding="UTF-8" location="classpath:loc/config.properties"
 ignore-resource-not-found="true" />

2 3.1后PropertySourcesPlaceholderConfigurer支持加载通配符*

<bean class="org.springframework.context.support.PropertySourcesPlaceholderConfigurer" p:location="classpath*:loc/*.properties"></bean> 

按ctrl点击标签可以看到spring-context.xsd中的详细信息。

PropertySourcesPlaceholderConfigurer类经过一系列继承关系，实质是一个容器后管理器。debug走里面的一段代码如下：

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>("environmentProperties", this.environment) {
 @Nullable
 public String getProperty(String key) {
 return ((Environment)this.source).getProperty(key);
 }
 });
 }

 try {
 PropertySource<?> localPropertySource = new PropertiesPropertySource("localProperties", this.mergeProperties());
 if (this.localOverride) {
 this.propertySources.addFirst(localPropertySource);
 } else {
 this.propertySources.addLast(localPropertySource);
 }
 } catch (IOException var3) {
 throw new BeanInitializationException("Could not load properties", var3);
 }
 }

 this.processProperties(beanFactory, (ConfigurablePropertyResolver)(new PropertySourcesPropertyResolver(this.propertySources)));
 this.appliedPropertySources = this.propertySources;
 }

进入这个mergeProperties()方法里面看：

 protected Properties mergeProperties() throws IOException {
 Properties result = new Properties();
 if (this.localOverride) {
 this.loadProperties(result);
 }

 if (this.localProperties != null) {
 Properties[] var2 = this.localProperties;
 int var3 = var2.length;

 for(int var4 = 0; var4 < var3; ++var4) {
 Properties localProp = var2[var4];
 CollectionUtils.mergePropertiesIntoMap(localProp, result);
 }
 }

 if (!this.localOverride) {
 this.loadProperties(result);
 }

 return result;
 }

可以看到localOverride这个属性是用来控制是否覆盖Spring读取的属性配置。并且下面紧跟着判断this.localProperties!=null,如果localProperties不为null的话，会读取这些配置信息到spring容易中并且覆盖spring中已存在的属性。

<!-- 这里的local-override="true" 就是覆盖spring容器中已存在的属性，properties-ref="dataSourceProperties" 是指定自己的properties -->
 <context:property-placeholder local-override="true" properties-ref="dataSourceProperties"
 file-encoding="UTF-8" location="classpath:loc/config.properties"
 ignore-resource-not-found="true" />
 <!-- 这个类是我自定义的，用来解密jdbc.properties中的属性之后然后存放到Properties类中 -->
 <bean id="dataSourceProperties" class="com.spring.demo.utils.DataSourceProperties">
 <constructor-arg value="encrypt.jdbc.password"/>
 </bean>

下面是我的DataSourceProperties类

package com.spring.demo.utils;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.util.Properties;

/**
 * 数据源配置参数处理
 * <p/>
 * 配置信息事先被DES加密处理，需要在此解密然后绑定到数据源
 * Created by Alvin on 2016/7/31.
 */
public class DataSourceProperties extends Properties {
 protected static final Logger logger = LoggerFactory.getLogger(AesUtils.class);
 /**
 * 构造方法
 * @param propertyNames 需要解密的属性名称
 */
 public DataSourceProperties(String[] propertyNames) {
 try {
 this.load(DataSourceProperties.class.getClassLoader()
 .getResourceAsStream("loc/config.properties"));
 for (String propertyName : propertyNames) {
 decrypt(propertyName);
 }
 } catch (IOException e) {
 logger.error(e.getMessage(),e);
 }
 }

 /**
 * 解密
 */
 private void decrypt(String propertyName) {
 logger.info("propertyName({}),value({})",propertyName,this.getProperty(propertyName));
 if (isEncryptPropertyVal(propertyName)){
 String value = AesUtils.decrypt(this.getProperty(propertyName), AesUtils.key);
 logger.info("propertyName({}),propertyValue({}),",propertyName,value);
 this.setProperty(propertyName, value);
 }
 }

 /**
 * 判断属性值是否需要解密，这里我约定需要解密的属性名用encrypt开头
 * @param propertyName
 * @return
 */
 private boolean isEncryptPropertyVal(String propertyName){
 if(propertyName.indexOf("encrypt") >= 0){
 return true;
 }else{
 return false;
 }
 }

}