十二：Servlet3.0的注解

1.@WebListener注解

表示的就是我们之前的在xml中配置的

<listener>
<listener-class>ListenerClass</listener-class>
</listener>

下面我们只需要在我们写好的Listener类上面加上这个@WebListener注解就OK啦

使用Listener的类必须使用下列的几个接口

ServletContextListener
ServletContextAttributeListener
ServletRequestListener
ServletRequestAttributeListener
HttpSessionListener
HttpSessionAttributeListener

例子：

package com.hotusm.web.listener;
 
import javax.servlet.annotation.WebListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
 
@WebListener
public class MyHttpSessionListener implements HttpSessionListener{
 
    @Override
    public void sessionCreated(HttpSessionEvent se) {
        System.out.println("创建session ");
    }
 
    @Override
    public void sessionDestroyed(HttpSessionEvent se) {
        System.out.println("销毁session ");
    }
 
}

这样，在我们启动的时候就会自动的帮助我们创建一个Listener了，这个注解有一个属性，是这个listener的描述信息

2.@WebFilter 这个注解就是表示的拦截器同样的也是直接注解在写好的Filter上面就ok了。

package com.hotusm.web.filter;
 
import javax.servlet.*;
import javax.servlet.annotation.WebFilter;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.http.HttpServletRequest;
import java.io.IOException;
 
@WebFilter(filterName = "filter1", urlPatterns="/*",
        dispatcherTypes = {DispatcherType.REQUEST, DispatcherType.FORWARD},
        initParams={@WebInitParam(name="account",value="1234"),@WebInitParam(name="hotusm",value="1234")}
        )
 
public class MyFilter implements Filter {
    @Override
    public void init(final FilterConfig filterConfig) throws ServletException {
 
        String account = filterConfig.getInitParameter("account");
        String hotusm = filterConfig.getInitParameter("hotusm");
 
        System.out.println("account:"+account+" hotusm:"+hotusm);
    }
 
    @Override
    public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain chain) throws IOException, ServletException {
        chain.doFilter(request, response);
    }
 
    @Override
    public void destroy() {
 
    }
}

注解的主要参数及其含义

3.@WebServlet 这个注解表示的就是一般的Servlet

package com.hotusm.web.servlet;
 
import javax.servlet.ServletException;
import javax.servlet.annotation.WebInitParam;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
 
import java.io.IOException;
 
@WebServlet(name = "servlet1", urlPatterns = {"/url1", "/url2","url3/*"}, loadOnStartup = 1,
        initParams = {
                @WebInitParam(name = "name", value="hotusm")
        })
public class MyServlet extends HttpServlet {
 
    private String name;
 
    public MyServlet() {
        System.out.println("load on startup");
    }
 
    @Override
    public void init() throws ServletException {
        super.init();
        name= this.getInitParameter("name");
    }
 
    @Override
    protected void doGet(final HttpServletRequest req, final HttpServletResponse resp) throws ServletException, IOException {
        HttpSession session = req.getSession();
        System.out.println(session);
        System.out.println("name:"+name);
    }
}

注解主要参数

参数和Filter差不多

4.其中在上面的注解Filter和Servlet用到的@WebInitParam 注解表示的就是参数啦相当于<init-param>

参数以及含义

5.@MultipartConfig 该注解主要是为了辅助 Servlet 3.0 中 HttpServletRequest 提供的对上传文件的支持。该注解标注在 Servlet 上面，以表示该 Servlet 希望处理的请求的 MIME 类型是 multipart/form-data。另外，它还提供了若干属性用于简化对上传文件的处理。具体如下：

通过上面的定义我们可以知道@MultipartConfig主要用来指明servlet的请求当中包含文件，文件我们通过以下的方式获取:
Part part = req.getPart("filename");

下面是一个简单的示例:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>upload your logo</title>
</head>
<body>
 
<form action="/multipart" method="post" enctype="multipart/form-data">
    Please choose your logo: <input type="file" name="logo"><br>
    <input type="submit" value="submit">
</form>
</body>
</html>

2 Servlet代码片段

import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.Part;
import java.io.IOException;
import java.io.PrintWriter;
 
@WebServlet(urlPatterns = {"/multipart"})
@MultipartConfig(location = "G:\\maven-practice\\sample-web\\files\\",
        maxFileSize = 2, maxRequestSize = 200)
public class MultipartServletDemo extends HttpServlet {
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        Part part = req.getPart("logo");
        PrintWriter out = resp.getWriter();
        out.println("file name: " + part.getName());
        out.println("file size: " + part.getSize());
        out.println("file content type: " + part.getContentType());
        out.println("upload successfully");
        out.flush();
        out.close();
    }
}