1.背景
ServletContext,是一个全局的储存信息的空间，服务器开始建立，服务器关闭销毁。request，每次请求一个；session，一个会话一个；而servletContext，所有用户共用一个。
ServletContext维护着一个服务器中的一个特定URL名字空间（比如，/myapplication）下的所有Servlet，Filter，JSP，JavaBean等Web部件的集合。
也就是说Servlet和Filter并不是由Spring ApplicationContext维护的，所以使用autowire注解来进行注入会产生问题。
一般都是通过下面这个方法解决
WebApplicationContext springContext = WebApplicationContextUtils.getWebApplicationContext(servletContextEvent.getServletContext());
2.准备工作
准备一个由Spring ApplicationContext维护Bean，分别在Listener、Filter和Servlet中调用其中的方法。
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
com.gqshao.spring.listener.MyListener
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;
/**
* 功能说明：测试自定义Listener使用spring使用注解定义的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
针对Filter，Spring提供了DelegatingFilterProxy解决
1.web.xml
MyFilter org.springframework.web.filter.DelegatingFilterProxy targetBeanName myFilter MyFilter /* REQUEST FORWARD
2.applicationContext.xml
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我们仿照Spring对Filter的处理写一个DelegatingServletProxy这样的代理Servlet
1.web.xml
myServlet com.gqshao.spring.servlet.DelegatingServletProxy myServlet /testservlet
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("Hello World
");
out.flush();
out.close();
}
}
4.说明
MyServlet使用Spring ApplicationContext来维护，通过@Component来定义
DelegatingServletProxy 通过web.xml文件中servlet-name中的值在Spring ApplicationContext中查找MyServlet，注意名称一致。