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();

    }

}