JavaWeb基础系列（二）Response

╰半橙微兮° 2021-09-26 23:12 495阅读 0赞

# 一、设置状态码 #

@WebServlet(name = "Servlet3",
            urlPatterns = {
       "/servlet3"}
    )
    public class Servlet3 extends HttpServlet { 
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            //手动设置http响应中的状态码
            response.setStatus(302);
    
        }
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        }
    }

运行结果：  
![这里写图片描述][70]

# 二、设置响应头 #

@WebServlet(name = "Servlet3",
            urlPatterns = {
       "/servlet3"}
    )
    public class Servlet3 extends HttpServlet { 
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            response.addHeader("name","naruto");
        }
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        }
    }

运行结果：  
![这里写图片描述][70 1]

# 三、重定向 #

特点：访问服务器两次，地址栏的地址发生变化  
重定向：状态码302  
响应头：Location，代表的是重定向的地址

@WebServlet(name = "Servlet3",
            urlPatterns = {
       "/Servlet3"}
    )
    public class Servlet3 extends HttpServlet { 
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            //没有响应资源，告知客户端去重定向的Servlet2
            //1、设置状态码302
            response.setStatus(302);
            //2、设置响应头Location
            response.setHeader("Location","/Servlet4");
        }
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        }
    }

运行结果：  
![这里写图片描述][70 2]  
Java将这些封装成重定向的方法sendRedirect(url)，所以要重定向我们也可以直接使用：  
response.sendRedirect(“/Servlet4”)；实现重定向

## 定时刷新 ##

@WebServlet(name = "Servlet3",
            urlPatterns = {
       "/Servlet3"}
    )
    public class Servlet3 extends HttpServlet { 
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            //设置定时刷新的头
            response.setHeader("refresh","5,url=http://www.baidu.com");
        }
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        }
    }

运行结果：5秒中之后，自动跳转到baidu页面去了  
![这里写图片描述][70 3]

# 四、使用js完成页面定时跳转 #

<!DOCTYPE html>
    <html>
        <head>
            <meta charset="UTF-8">
            <title></title>
            <script type="text/javascript"> window.onload = function(){ var time = 5; var secondEle = document.getElementById("second"); var timer = setInterval(function(){ secondEle.innerHTML = time; time--; if(time == 0){ clearInterval(timer); location.href="http://www.baidu.com"; } },1000); } </script>
        </head>
        <body>
            恭喜你，注册成功，<span style="color: red" id="second">5</span>秒钟后跳转，如不跳转点击<a href="http://www.baidu.com">这里！
        </body>
    </html>

# 五、使用response的writer #

@WebServlet(name = "Servlet3",
            urlPatterns = {
       "/Servlet3"}
    )
    public class Servlet3 extends HttpServlet { 
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            PrintWriter writer = response.getWriter();
            writer.write("hello response");
    
        }
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        }
    }

运行结果：输出hello response  
但是当我们使用：

PrintWriter writer = response.getWriter();
    writer.write("中国");

输出的是两个问号！  
所以先要设置response查询的码表和客户端解码的码表：

@WebServlet(name = "Servlet3",
            urlPatterns = {
       "/Servlet3"}
    )
    public class Servlet3 extends HttpServlet { 
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            //设置response查询的码表
            response.setCharacterEncoding("UTF-8");
            //通过头Contend-Type告知客户端使用何种码表进行解码
            response.setHeader("Content-Type","text/html;charset=UTF-8");
            PrintWriter writer = response.getWriter();
            writer.write("中国");
    
        }
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        }
    }

运行结果：  
![这里写图片描述][70 4]  
实际开发中，写response.setHeader(“Content-Type”,”text/html;charset=UTF-8”);就可以了，因为检测到这句代码之后，tomcat会自动将response查询的码表改成UTF-8的。  
Java也为这句话封装了一个方法：  
response.setContentType(“text/html;charset=UTF-8”);实现上述功能

# 六、使用response的outputstream #

@WebServlet(name = "Servlet3",
            urlPatterns = {
       "/Servlet3"}
    )
    public class Servlet3 extends HttpServlet { 
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            //使用response获得字节输出流
            ServletOutputStream out = response.getOutputStream();
            //获得服务器上的图片
            String realPath = this.getServletContext().getRealPath("6.jpg");
            InputStream in = new FileInputStream(realPath);
            int len;
            byte[] buffer = new byte[1024];
            while((len=in.read(buffer))>0){
                out.write(buffer,0,len);
            }
            in.close();
            out.close();
        }
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
        }
    }

运行结果：将图片从服务器读出来，然后到客户端显示。  
![这里写图片描述][70 5]

# 七、文件下载 #

问题：  
1）什么情况下会有文件下载？  
浏览器不能解析的文件就下载。  
2）什么情况情况下需要在服务端编写文件下载的代码？  
理论上，浏览器可以解析的代码需要编写文件下载代码，实际开发中，只要是下载的文件都编写文件下载代码。  
html代码：

<!DOCTYPE html>
    <html>
        <head>
            <meta charset="UTF-8">
            <title></title>
        </head>
        <body>
              <h1>使用服务器端编码的方式实现文件下载</h1><br>
              <a href="/Servlet4?filename=6.jpg">6.jpg</a>
        </body>
    </html>

Servlet代码：

package com.servlet;
    
    @WebServlet(name = "Servlet4",
            urlPatterns = {
       "/Servlet4"})
    public class Servlet4 extends HttpServlet { 
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            doGet(request,response);
        }
    
        protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            //获得要下载的文件的名称
            String filename = request.getParameter("filename");
            //要下载的这个文件的类型--客户端通过文件的MIME类型去区分类型
            response.setContentType(this.getServletContext().getMimeType(filename));
            //告诉客户端该文件不能直接解析，而是以附件形式打开（下载）
            response.setHeader("Content-Disposition","attachment;filename="+filename);
            //获得该文件的绝对路径
            String path = this.getServletContext().getRealPath(filename);
            System.out.println(path);
            //获得该文件的输入流
            FileInputStream in = new FileInputStream(path);
            //获得输出流--通过response获得的输出流，用于向客户端写内容
            ServletOutputStream out = response.getOutputStream();
            //文件拷贝模版代码
            int len;
            byte[] buffer = new byte[1024];
            while((len=in.read(buffer))>0){
                out.write(buffer,0,len);
            }
            in.close();
            out.close();
        }
    }

运行结果：![这里写图片描述][70 6]  
中文名乱码问题：

package com.itheima.content;
    
    import java.io.FileInputStream;
    import java.io.IOException;
    import java.io.InputStream;
    import java.net.URLEncoder;
    
    import javax.servlet.ServletException;
    import javax.servlet.ServletOutputStream;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    import sun.misc.BASE64Encoder;
    
    public class DownLoadServlet2 extends HttpServlet { 
        protected void doGet(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
            //*******文件名称是中文的下载*******
            //获得要下载的文件的名称
            String filename = request.getParameter("filename");//????.jpg
            //解决获得中文参数的乱码----下节课讲
            filename = new String(filename.getBytes("ISO8859-1"),"UTF-8");//美女.jpg
    
            //获得请求头中的User-Agent
            String agent = request.getHeader("User-Agent");
            //根据不同浏览器进行不同的编码
            String filenameEncoder = "";
            if (agent.contains("MSIE")) {
                // IE浏览器
                filenameEncoder = URLEncoder.encode(filename, "utf-8");
                filenameEncoder = filenameEncoder.replace("+", " ");
            } else if (agent.contains("Firefox")) {
                // 火狐浏览器
                BASE64Encoder base64Encoder = new BASE64Encoder();
                filenameEncoder = "=?utf-8?B?"
                        + base64Encoder.encode(filename.getBytes("utf-8")) + "?=";
            } else {
                // 其它浏览器
                filenameEncoder = URLEncoder.encode(filename, "utf-8");             
            }
    
            //要下载的这个文件的类型-----客户端通过文件的MIME类型去区分类型
            response.setContentType(this.getServletContext().getMimeType(filename));
            //告诉客户端该文件不是直接解析 而是以附件形式打开(下载)----filename="+filename 客户端默认对名字进行解码
            response.setHeader("Content-Disposition", "attachment;filename="+filenameEncoder);
    
            //获取文件的绝对路径
            String path = this.getServletContext().getRealPath("download/"+filename);
            //获得该文件的输入流
            InputStream in = new FileInputStream(path);
            //获得输出流---通过response获得的输出流 用于向客户端写内容
            ServletOutputStream out = response.getOutputStream();
            //文件拷贝的模板代码
            int len = 0;
            byte[] buffer = new byte[1024];
            while((len=in.read(buffer))>0){
                out.write(buffer, 0, len);
            }
            in.close();
            //out.close();
    
        }
    
        protected void doPost(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
            doGet(request, response);
        }
    }

reponse细节点：  
1）response获得的流不需要手动关闭，Tomcat容器会帮助我们关闭  
2）getWriter和getOutputStream不能同时调用

[70]: /images/20210923/1d1c22b95c3d4981848fefd7d37524a7.png
[70 1]: /images/20210923/f4e0f3092bb64365bfb8c62dcee57fb1.png
[70 2]: /images/20210923/cdc9eb4bd62e44d7827f2268912625ad.png
[70 3]: /images/20210923/b76d418b3c0149c19395f292cfaa539f.png
[70 4]: /images/20210923/51bd0ed53de04797808dc16a7c71d657.png
[70 5]: /images/20210923/3cca6db8ce174c14a25161a9ec2de7f3.png
[70 6]: /images/20210923/cb5e1df9f0684fdab145bc98292db6cb.png