spring服务定位器类

此文章是基于　　搭建Jquery+SpringMVC+Spring+Hibernate+MySQL平台

功能：通过持有的Spring应用场景ApplicationContext，可在任何地方获取bean。

1. 服务定位器类：ServiceLocator.java

package com.ims.common;

import org.apache.log4j.Logger;
import org.springframework.beans.factory.DisposableBean;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

/**
 * 服务定位器
 * 持有Spring的应用场景, 可在任何地方获取bean.
 */
public final class ServiceLocator implements ApplicationContextAware, DisposableBean {
    
    private static Logger logger = Logger.getLogger(ServiceLocator.class);
    private static ApplicationContext context = null;
    
    /**
     * 实现ApplicationContextAware接口, 注入Context到静态变量中.
     * @param context
     */
    @Override
    public void setApplicationContext(ApplicationContext context) {        
        logger.debug("Injected the ApplicationContext into ServiceLocator:" + context);
        if (ServiceLocator.context != null) {
            logger.debug("[------------ ApplicationContext in the ServiceLocator " +
                                "is covered, as the original ApplicationContext is:"
                                            + ServiceLocator.context + " ------------]");
        }
        ServiceLocator.context = context; 
    }
    
    /**
     * 实现DisposableBean接口,在Context关闭时清理静态变量.
     */
    @Override
    public void destroy() throws Exception {
        ServiceLocator.clear();
    }
    
    /**
     * 取得存储在静态变量中的ApplicationContext.
     * @return
     */
    public static ApplicationContext getApplicationContext() {
        assertContextInjected();
        return context;
    }
    
    /**
     * 从Spring的应用场景中取得Bean, 自动转型为所赋值对象的类型.
     * @param name bean名称
     * @return bean对象
     */
    @SuppressWarnings("unchecked")
    public static <T> T getService(String name) {
        assertContextInjected();
        return (T) context.getBean(name);
    }
    
    /**
     * 从Spring的应用场景中取得Bean, 自动转型为所赋值对象的类型.
     * @param requiredType bean类
     * @return bean对象
     */
    public static <T> T getService(Class<T> requiredType) {
        assertContextInjected();
        return context.getBean(requiredType);
    }
    
    /**
     * 清除ServiceLocator中的ApplicationContext
     */
    public static void clear() {
        logger.debug("Clear ApplicationContext in ServiceLocator :" + context);
        context = null;
    }
    
    /**
     * 检查ApplicationContext不为空.
     */
    private static void assertContextInjected() {
        if (context == null) {
            throw new IllegalStateException("ApplicaitonContext not injected, " +
                            "as defined in the context.xml ServiceLocator");
        }
    }
}

2. Spring上下文场景加载监听器：SpringContextLoaderListener.java

package com.ims.web;

import javax.servlet.ServletContextEvent;

import org.springframework.web.context.ContextLoaderListener;

import com.ims.common.ServiceLocator;

/**
 * Spring场景加载监听器，用于加载/销毁Spring场景
 */
public class SpringContextLoaderListener extends ContextLoaderListener {
    
    private final ServiceLocator locator = new ServiceLocator();
    
    public SpringContextLoaderListener() {
        super();
    }
    

    @Override
    public void contextInitialized(ServletContextEvent event) {
        super.contextInitialized(event);
        
        // 将Spring场景置入服务定位器中
        locator.setApplicationContext(getCurrentWebApplicationContext());                
    }
    
    
    @Override
    public void contextDestroyed(ServletContextEvent event) {
        try {
            locator.destroy();
        } 
        catch (Exception e) {
            e.printStackTrace();
        }        
        
        super.contextDestroyed(event);            
    }
}

3. 修改 web.xml

如果存在如下代码，则去掉

<listener>   
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>   
  </listener>

然后添加上如下代码：

<listener>
     <listener-class>com.ims.web.SpringContextLoaderListener</listener-class>
  </listener>

4. 在 src/applicationContext.xml 中添加如下代码：

<bean class="com.ims.common.ServiceLocator"/>

5. 调用 ServiceLocator.java 中的 getService 函数，可分为按名称或类型获取bean。