javaweb之Servlet中response对象

一，概述

功能：设置响应消息
1，设置响应行
格式：HTTP/1.1 200 ok
设置状态码：setStatus(int sc)

2，设置响应头：
setHeader(String name, String value)

3，设置响应体：

使用步骤：
（1），获取输出流
字符输出流：PrintWriter getWriter()
字节输出流：ServletOutputStream getOutputStream()
（2），使用输出流，将数据输出到客户端浏览器

二，重定向案例

@WebServlet("/responseDemo1")
public class ResponseDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("demo...");

        
        response.setStatus(302);
        /*
        response.setHeader("location","/day4/responseDemo2");
        */

        //动态获取虚拟目录
        String contextPath = request.getContextPath();
        response.sendRedirect(contextPath + "/responseDemo2");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

@WebServlet("/responseDemo2")
public class ResponseDemo2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println("demo2....");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

forward和redirect区别：

重定向的特点:redirect
1，地址栏发生变化
2，重定向可以访问其他站点(服务器)的资源
3，重定向是两次请求。不能使用request对象来共享数据

转发的特点：forward
1，转发地址栏路径不变
2，转发只能访问当前服务器下的资源
3，转发是一次请求，可以使用request对象来共享数据

路径写法：
1，路径分类

1. 相对路径：通过相对路径不可以确定唯一资源，如：./index.html、不以/开头，以.开头路径
   规则：找到当前资源和目标资源之间的相对位置关系
   ./：当前目录
   …/:后退一级目录
2. 绝对路径：通过绝对路径可以确定唯一资源，如：http://localhost/day15/responseDemo2 /day15/responseDemo2、以/开头的路径；
   规则：判断定义的路径是给谁用的？判断请求将来从哪儿发出
   给客户端浏览器使用：需要加虚拟目录(项目的访问路径)，建议虚拟目录动态获取：request.getContextPath()，如<a> , <form>重定向…
   给服务器使用：不需要加虚拟目录，如转发路径。

三，服务器输出数据到浏览器

1，服务器输出字符数据到浏览器：
步骤：
（1），获取字符输出流
（2），输出数据

注意：乱码问题：
（1），PrintWriter pw = response.getWriter();获取的流的默认编码是ISO-8859-1
（2），设置该流的默认编码
（3），告诉浏览器响应体使用的编码

//简单的形式，设置编码，是在获取流之前设置
response.setContentType("text/html;charset=utf-8");

2，服务器输出字节数据到浏览器
步骤：
（1）.获取字节输出流
（2）.输出数据

@WebServlet("/responseDemo3")
public class ResponseDemo3 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置响应消息体的编码
        response.setContentType("text/html;charset=utf-8");
        //获取流
        PrintWriter pw = response.getWriter();

        pw.write("你好啊，response...");
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

@WebServlet("/responseDemo4")
public class ResponseDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
        response.setContentType("text/html;charset=utf-8");
        ServletOutputStream sos = response.getOutputStream();
        sos.write("你好".getBytes("utf-8"));
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        this.doPost(request,response);
    }
}

3，验证码案例：

1. 本质：图片
2. 目的：防止恶意表单注册

@WebServlet("/checkCodeDemo1")
public class CheckCodeDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
        int width = 200;
        int height = 100;
        //创建图片对象
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);

        //美化图片
        Graphics gh = image.getGraphics();
        gh.setColor(Color.PINK);
        gh.fillRect(0,0,width,height);//填充矩形

        gh.setColor(Color.BLUE);
        gh.drawRect(0,0,width-1,height-1);//画边框

        Random rd = new Random();
        String s = "qwertyuiopasdfghjklzxcvbnmQWERTYUIOPASDFGHJKLZXCVBNM1234567890";
        for (int i = 1; i <= 4; i++) {
            int index = rd.nextInt(s.length());
            char ch = s.charAt(index);
            gh.drawString(ch+"",width/5*i,height/2);
        }

        gh.setColor(Color.GREEN);
        for (int i = 0; i < 10; i++) {
            int x1 = rd.nextInt(width);
            int x2 = rd.nextInt(width);
            int y1 = rd.nextInt(height);
            int y2 = rd.nextInt(height);
            gh.drawLine(x1,y1,x2,y2);

        }


        //将图片输出到页面展示
        ImageIO.write(image,"jpg",response.getOutputStream());

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        this.doPost(request,response);
    }
}

前端页面：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <script>
        window.onload = function () {
            var checkImag = document.getElementById("checkImag");
            checkImag.onclick = function () {
                var time = new Date().getTime();
                checkImag.src = "/day4/checkCodeDemo1?"+time;
            };
        };

        function testClick() {
            var checkImag = document.getElementById("checkImag");
            var time = new Date().getTime();
            checkImag.src = "/day4/checkCodeDemo1?"+time;

        }
    </script>
</head>
<body>
    <img id="checkImag" src="/day4/checkCodeDemo1" alt="">

    <a id="nextImge" href="javascript:testClick()">看不清？点击下一张</a>
</body>
</html>

四，ServletContext对象

1，概念：代表整个web应用，可以和程序的容器(服务器)来通信

2，获取：

1. 通过request对象获取，request.getServletContext();
2. 通过HttpServlet获取，this.getServletContext();

@WebServlet("/servletContextDemo1")
public class ServletContextDemo1 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext context1 = this.getServletContext();
        ServletContext context2 = request.getServletContext();
        System.out.println(context1);
        //[e-mail]
        System.out.println(context2);
        //[e-mail]
        System.out.println(context1 == context2); //true
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

3，功能：

（1），获取MIME类型：
MIME类型:在互联网通信过程中定义的一种文件数据类型
格式： 大类型/小类型 text/html image/jpeg
获取：String getMimeType(String file)

@WebServlet("/servletContextDemo2")
public class ServletContextDemo2 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        String filename = "视频.mp4";
        //1，获取MIME类型（文件类型）
        String mimeType = context.getMimeType(filename);
        System.out.println(mimeType);
        // video/mp4
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

（2），域对象：共享数据
setAttribute(String name,Object value)
getAttribute(String name)
removeAttribute(String name)
ServletContext对象范围：所有用户所有请求的数据

@WebServlet("/servletContextDemo3")
public class ServletContextDemo3 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext context1 = this.getServletContext();
        context1.setAttribute("msg","正确");

    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

@WebServlet("/servletContextDemo4")
public class ServletContextDemo4 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        Object msg = context.getAttribute("msg");
        System.out.println(msg);//正确
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

3，获取文件的真实(服务器)路径

方法：

@WebServlet("/servletContextDemo5")
public class ServletContextDemo5 extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        ServletContext context = this.getServletContext();
        //获取资源真实路径
        String realPath1 = context.getRealPath("/b.txt");

        String realPath2 = context.getRealPath("/WEB-INF/c.txt");

        String realPath3 = context.getRealPath("/WEB-INF/class/a.txt");

        System.out.println(realPath1);
        System.out.println(realPath2);
        System.out.println(realPath3);
        /*
            E:\Java_Project\out\artifacts\day4_war_exploded\b.txt
            E:\Java_Project\out\artifacts\day4_war_exploded\WEB-INF\c.txt
            E:\Java_Project\out\artifacts\day4_war_exploded\WEB-INF\class\a.txt
         */
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

五，servlet文件下载案例

文件下载需求：

1. 页面显示超链接
2. 点击超链接后弹出下载提示框
3. 完成图片文件下载

分析：

1. 超链接指向的资源如果能够被浏览器解析，则在浏览器中展示，如果不能解析，则弹出下载提示框。不满足需求
2. 任何资源都必须弹出下载提示框
3. 使用响应头设置资源的打开方式：content-disposition:attachment;filename=xxx

步骤：

1. 定义页面，编辑超链接href属性，指向Servlet，传递资源名称filename
2. 定义Servlet
   （1），获取文件名称
   （2），使用字节输入流加载文件进内存
   （3），指定response的响应头： content-disposition:attachment;filename=xxx
   （4），将数据写出到response输出流

@WebServlet("/downloadServlet")
public class DownloadServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //将文件写入内存
        String filename = request.getParameter("filename");
        ServletContext context = request.getServletContext();
        String realPath = context.getRealPath("/source/" + filename);
        System.out.println(realPath);
        FileInputStream fis = new FileInputStream(realPath);

        //设置头信息，以附件形式
        String mimeType = context.getMimeType(filename);
        response.setHeader("content-type",mimeType);
        String agent = request.getHeader("user-agent");
        //使用工具包，适配各个浏览器中文乱码问题
        filename = DownLoadUtils.getFileName(agent,filename);
        response.setHeader("content-disposition","attachment;filename="+filename);

        //将资源写到页面上
        ServletOutputStream sos = response.getOutputStream();
        byte[] bytes = new byte[1024];
        int len = 0;


        while ((len = fis.read(bytes)) != -1){
            sos.write(bytes,0,len);
        }

        fis.close();
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }
}

DownLoadUtils工具包：

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.util.Base64;
import java.util.Base64.Encoder;


public class DownLoadUtils {

    public static String getFileName(String agent, String filename) throws UnsupportedEncodingException {
        if (agent.contains("MSIE")) {
            // IE浏览器
            filename = URLEncoder.encode(filename, "utf-8");
            filename = filename.replace("+", " ");
        } else if (agent.contains("Firefox")) {
            // 火狐浏览器
            Encoder encoder = Base64.getEncoder();
            filename = "=?utf-8?B?" + encoder.encodeToString(filename.getBytes("utf-8")) + "?=";

        } else {
            // 其它浏览器
            filename = URLEncoder.encode(filename, "utf-8");
        }
        return filename;
    }

}

前端页面
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <a href="/day4/source/1.jpg">图片1</a>
    <a href="/day4/source/01.avi">视频1</a>
    <br>
    <a href="/day4/downloadServlet?filename=皮卡丘.jpg">图片2</a>
    <a href="/day4/downloadServlet?filename=java传智.avi">视频2</a>

</body>
</html>