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  • JavaWeb学习笔记（9）

     ServletContext

    Context:上下文

    ServletContext: 代表的是整个应用。一个应用只有一个ServletContext对象。是单例对象。

    作用：

    域对象：在一定范围内（当前应用），使多个Servlet共享数据。

    常用方法：

    • void setAttribute(String name,object value);//向ServletContext对象的map中添加数据  
    • Object getAttribute(String name);//从ServletContext对象的map中取数据
    • void rmoveAttribute(String name);//根据name去移除数据
    package com.zx.web.lesson01;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@WebServlet("/Lesson01Servlet1")
public class Lesson01Servlet1 extends HttpServlet{
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        //1.获取一个应用的上下文
        ServletContext context=this.getServletContext();
        System.out.println(context);
        
        //2.往上下文存数据
        context.setAttribute("name", "zx it caiji");
        
    }
}
    package com.zx.web.lesson02;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@WebServlet("/Lesson02Servlet1")
public class Lesson02Servlet1 extends HttpServlet{
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        /**
         * 注意：在web.xml中context-param配置的信息不是通过getAttribute方法获取的
         */
        //String str=(String) this.getServletContext().getAttribute("encoding");
        String str=(String) this.getServletContext().getInitParameter("encoding");
        System.out.println("web.xml中获取的encoding 值："+str);
    }
}


结果：
web.xml中获取的encoding 值：utf-8

    String getRealPath(String path);

    ü  根据资源名称得到资源的绝对路径.

    ü  可以得到当前应用任何位置的任何资源。

    package com.zx.web.lesson03;

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Properties;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@WebServlet("/Lesson03Servlet1")
public class Lesson03Servlet1 extends HttpServlet{
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        /**
         * 通过浏览器地址栏访问的路径都是get请求
         */
        /**
         * String path="src\com\zx\web\lesson03\info.properties";
         * 如果是web项目，查找文件时，要从类路径找
         */
        //String path="src\com\zx\web\lesson03\info.properties";
        String path=this.getServletContext().getRealPath("WEB-INF\classes\com\zx\web\lesson03\info.properties");
        System.out.println(path);
        //在Servlet中获取info.properties数据
        //1.创建属性对象
        Properties pro=new Properties();
        
        //2.关联属性文件的路径
        pro.load(new FileInputStream(path));
        
        System.out.println(pro.getProperty("username"));
        
        //响应客户端
        resp.getWriter().write(path);
    }
}

     Servlet的转发

    package com.zx.web.lesson04;

import java.io.IOException;

import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@WebServlet("/Lesson04Servlet1")
public class Lesson04Servlet1 extends HttpServlet{
    
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        /**
         * request:请求
         * response:响应,给客户端响应数据
         */
        //response.getWriter().write("data from servlet1");
        //1.获取请求转发的对象
        RequestDispatcher rd= request.getRequestDispatcher("/Lesson04Servlet2");
        
        //2.执行转发
        rd.forward(request, response);
    }
}
    package com.zx.web.lesson04;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@WebServlet("/Lesson04Servlet2")
public class Lesson04Servlet2 extends HttpServlet{
    
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        /**
         * request:请求
         * response:响应
         */
        response.getWriter().write("data from servlet2");
    }
}

    HTTP：

    HTTP消息头

    • HTTP消息头是指在超文本传输协议（ Hypertext Transfer Protocol ，HTTP）的请求和响应消息中，协议头部分的那些组件。
    • HTTP消息头用来准确描述正在获取的资源、服务器或者客户端的行为
    • HTTP消息头定义了HTTP事务中的具体操作参数。
    • 消息头包括请求时的消息头（请求头）和响应时的消息头（响应头）

    HttpServletResponse

    Web服务器收到客户端的http请求，会针对每一次请求，分别创建一个用于代表请求的request对象、和代表响应的response对象。

    响应正文（主体）

    getWrite(); 字符输出流

    getOutputStream(); 字节输出流,可以用来下载文件

    响应编码

    案例：向客户端输出中文

    package com.zx.web.lesson06;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@WebServlet("/Lesson06Servlet2")
public class Lesson06Servlet2 extends HttpServlet{
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        //响应编码问题
        
        //1.设置响应头
        //resp.setContentType("text/html");//设置响应的类型
        //resp.setCharacterEncoding("UTF-8");        //设置响应的编码类型
        
        //另外一种解决乱码的写法
        resp.setHeader("Content-Type", "text/html;charset=UTF-8");
        resp.getWriter().write("张无改-张又改");
    }
}

    响应状态码

    常见的状态码参照：http://tool.oschina.net/commons?type=5

    404请求失败，请求所希望得到的资源未被在服务器上发现

    200请求已成功，请求所希望的响应头或数据体将随此响应返回。

    302 重定向

    500 服务抛出异常

    package com.zx.web.lesson07;

import java.io.IOException;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@WebServlet("/Lesson07Servlet1")
public class Lesson07Servlet1 extends HttpServlet{
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        
        //响应状态码
        /**
         * 默认情况下，服务器响应给客户端的状态码为200
         * 200:ok，没有问题
         */
        resp.setStatus(404);
        resp.getOutputStream().write("hello".getBytes());
    }
}

    文件下载

    package com.zx.web.lesson08;

import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@WebServlet("/Lesson08Servlet1")
public class Lesson08Servlet1 extends HttpServlet{
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        
        //处理文件下载[把文件的数据（二进制）响应给客户端]
        //1.文件名
        String fileName="啥子.jpg";
        String path="E:\"+fileName;
        /**
         * 注意：如果是文件下载，需要设置响应头Content-disposition
         * 如果文件名中有中文，下载时为了解决乱码问题，需要对文本进行URLEncode,把中文变成百分号形式%
         * 哈哈.txt=%E5%93%88%E5%93%88.txt
         * 一个中文会对应三个百分号数据
         */
        //设置响应类型
        fileName=URLEncoder.encode(fileName, "UTF-8");
        System.out.println(fileName);
        resp.setHeader("Content-disposition", "attachment;filename=" + fileName);
        
        //2.获取文件输入流
        FileInputStream fis=new FileInputStream(path);
        
        //3.获取输出流
        ServletOutputStream sos= resp.getOutputStream();
        
        //4.从文件中读取数据，响应给客户端
        byte[] buf=new byte[1024];
        int len=0;
        while ((len=fis.read(buf))!=-1) {
            sos.write(buf, 0, len);
        }
        
        //关闭资源(输出流会自动关闭)
        fis.close();
    }
}

     手写验证码

    package com.zx.web.lesson09;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


@WebServlet("/VerificationCode")
public class VerificationCode extends HttpServlet{
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        //1.创建一个图片对象
        int width=120;
        int height=30;
        BufferedImage bi=new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        
        //2.拿到画笔
        Graphics graphics= bi.getGraphics();
        
        //3.涂个背景颜色
        graphics.setColor(Color.yellow);//设置画笔颜色
        graphics.fillRect(0, 0, width, height);
        
        //4.画干扰线
        //重新设置画笔颜色
        graphics.setColor(Color.BLACK);
        Random random=new Random();
        for (int i=0;i<4;i++) {
            //第一个点
            int x1=random.nextInt(width);
            int y1=random.nextInt(height);
            
            //第二个点
            int x2=random.nextInt(width);
            int y2=random.nextInt(height);
            graphics.drawLine(x1, y1, x2, y2);
        }
        
        //5.画验证码（4个随机数）
        graphics.setColor(Color.RED);
        int left=10;
        for (int i=0;i<4;i++) {
            int r=random.nextInt(10);
            graphics.drawString(r+"", (left+i*30), 20);
        }
        
        //设置响应类型
        resp.setContentType("image/jpeg");
        //把图片输出给客户端
        ImageIO.write(bi, "JPEG", resp.getOutputStream());
    }
}
    <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>Insert title here</title>
<script type="text/javascript">
    function refreshCode(){
        //1.获取img标签
        var imgTag=document.getElementById("code");
        //2.获取img标签src的属性值
        console.log(imgTag.src);
        //3.重新赋值
        imgTag.src="/day09Web/VerificationCode?"+new Date().getTime();//改的值与原本的src一致，js就不会去访问后台
    }
</script>
</head>
<body>
<form action="">
    用户名：<input type="text"><br/>
    密码：<input type="password"><br/>
    <!-- src下面要添加项目名称 -->
    验证码：<input type="text">
    <img id="code" alt="" src="/day09Web/VerificationCode">
    <!-- 怎么在a标签中，调用js -->
    <a href="javascript:refreshCode()">看不清，换一张</a>
</form>
</body>
</html>

    使用工具类实现验证码

    package com.zx.web.lesson10;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;
import java.util.Random;

import javax.imageio.ImageIO;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import cn.dsna.util.images.ValidateCode;


@WebServlet("/VerificationCode2")
public class VerificationCodeServlet extends HttpServlet{
    
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        //使用工具来生成验证码,一个jar包
        /**
         * JavaWeb中，导入第三方的包，跟以前有点不一样
         * 导包都是放在WEB_INF/lib
         */
        //创建验证码对象
        ValidateCode validateCode=new ValidateCode(100, 30, 4, 6);
        
        //把验证码返回给客户端
        validateCode.write(resp.getOutputStream());
    }
}

     自动刷新响应头

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.setContentType("text/html;charset=UTF-8");
        //response.setHeader("Refresh", "1");//每隔一秒刷新一次
        
        response.setHeader("Refresh", "5;URL=index.html");//3秒后转到另一页面
        response.getWriter().write("注册成功!3秒后会自动跳转，苦没有中转点击<a href='index.html'>这里</a>");
    }

    response需要注意的细节：

    1. getOutputStream和getWriter这两个方法互相排斥，调用了其中的任何一个方法后，就不能再调用另一方法。  会抛异常
    2. 这两个流不需要我们关闭，如果自己写close方法也没有问题，但是这样做等于重复做事

    HttpServletRequest

    request常用方法

    获得客户端信息

    • getRequestURL方法返回客户端发出请求时的完整URL。
    • getRequestURI方法返回请求行中的资源名部分。
    • getQueryString 方法返回请求行中的参数部分。
    • getRemoteAddr方法返回发出请求的客户机的IP地址
    • getRemoteHost方法返回发出请求的客户机的完整主机名
    • getRemotePort方法返回客户机所使用的网络端口号
    • getLocalAddr方法返回WEB服务器的IP地址。
    • getLocalName方法返回WEB服务器的主机名
    • getMethod得到客户机请求方式

    获得客户端请求头

    • getHead(name)方法
    • getHeaders(String name)方法
    • getHeaderNames方法
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  • 原文地址：https://www.cnblogs.com/zhangwugai/p/11299480.html
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