如何在Listener、Filter、Servlet中調用 spring 使用註解定義的bean

轉載聲明：本文章轉載自https://sgq0085.iteye.com/blog/2191110

1.背景

    ServletContext,是一個全局的儲存信息的空間，服務器開始建立，服務器關閉銷燬。request，每次請求一個；session，一個會話一個；而servletContext，所有用戶共用一個。

 ServletContext維護着一個服務器中的一個特定URL名字空間（比如，/myapplication）下的所有Servlet，Filter，JSP，JavaBean等Web部件的集合。

    也就是說Servlet和Filter並不是由Spring ApplicationContext維護的，所以使用autowire註解來進行注入會產生問題。

一般都是通過下面這個方法解決

WebApplicationContext springContext = WebApplicationContextUtils.getWebApplicationContext(servletContextEvent.getServletContext());

2.準備工作

準備一個由Spring ApplicationContext維護Bean，分別在Listener、Filter和Servlet中調用其中的方法

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

@Component("springBean")
public class SpringBean {

    private static final Logger logger = LoggerFactory.getLogger(SpringBean.class);

    public void listener() {
        logger.info("listener use spring bean");
    }

    public void servlet() {
        logger.info("servlet use spring bean");
    }

    public void filter() {
        logger.info("filter use spring bean");
    }


}

2.Listener

1.web.xml

<!-- test listener use spring bean -->
<listener>
    <listener-class>com.gqshao.spring.listener.MyListener</listener-class>
</listener>

2.MyListener

package com.gqshao.spring.listener;

import com.gqshao.spring.bean.SpringBean;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

/**
 * 功能說明：測試自定義Listener使用spring使用註解定義的bean
 */
public class MyListener implements ServletContextListener {

    private static final Logger logger = LoggerFactory.getLogger(MyListener.class);


    @Override
    public void contextInitialized(ServletContextEvent event) {
        WebApplicationContext springContext = WebApplicationContextUtils.getWebApplicationContext(event.getServletContext());
        SpringBean bean = (SpringBean) springContext.getBean("springBean");
        bean.listener();
    }

    @Override
    public void contextDestroyed(ServletContextEvent sce) {
        logger.info("MyListener contextDestroyed");
    }
}

3.Filter

針對Filter，Spring提供了DelegatingFilterProxy解決

1.web.xml

<!-- test filter use spring bean -->
<filter>
    <filter-name>MyFilter</filter-name>
    <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
    <init-param>
        <param-name>targetBeanName</param-name>
        <param-value>myFilter</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>MyFilter</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>FORWARD</dispatcher>
</filter-mapping>

2.applicationContext.xml

<bean name="myFilter" class="com.gqshao.spring.filter.MyFilter"/>

3.MyFilter

package com.gqshao.spring.filter;


import com.gqshao.spring.bean.SpringBean;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;

import javax.servlet.*;
import java.io.IOException;

public class MyFilter implements Filter {

    private static final Logger logger = LoggerFactory.getLogger(MyFilter.class);

    @Autowired
    private SpringBean springBean;

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        logger.info("MyFilter init");
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException {
        springBean.filter();
        filterChain.doFilter(request, response);
    }

    @Override
    public void destroy() {
        logger.info("MyFilter destroy");
    }
}

3.Servlet

Servlet我們仿照Spring對Filter的處理寫一個DelegatingServletProxy這樣的代理Servlet

1.web.xml

<!-- test servlet use spring bean -->
<servlet>
    <servlet-name>myServlet</servlet-name>
    <servlet-class>com.gqshao.spring.servlet.DelegatingServletProxy</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>myServlet</servlet-name>
    <url-pattern>/testservlet</url-pattern>
</servlet-mapping>

2.DelegatingServletProxy

package com.gqshao.spring.servlet;

import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;

import javax.servlet.*;
import java.io.IOException;

public class DelegatingServletProxy extends GenericServlet {

    private String targetBean;
    private Servlet proxy;

    @Override
    public void service(ServletRequest request, ServletResponse response) throws ServletException,
            IOException {
        proxy.service(request, response);
    }

    @Override
    public void init() throws ServletException {
        this.targetBean = getServletName();
        setServletBean();
        proxy.init(getServletConfig());
    }

    private void setServletBean() {
        WebApplicationContext wac = WebApplicationContextUtils.getRequiredWebApplicationContext(getServletContext());
        this.proxy = (Servlet) wac.getBean(targetBean);
    }
}

3.MyServlet

package com.gqshao.spring.servlet;

import com.gqshao.spring.bean.SpringBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;

@Component
public class MyServlet extends HttpServlet {

    @Autowired
    private SpringBean springBean;

    public void service(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        springBean.servlet();
        PrintWriter out = response.getWriter();
        out.println("<h3>Hello World</h3>");
        out.flush();
        out.close();
    }
}

4.說明

MyServlet使用Spring ApplicationContext來維護，通過@Component來定義

DelegatingServletProxy 通過web.xml文件中servlet-name中的值在Spring ApplicationContext中查找MyServlet，注意名稱一致。