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JavaWeb入门:HttpResponse和HttpRequest详解

来源：互联网收集：自由互联发布时间：2021-08-21

目录 HttpResponse 讲解 HttpServletResponse概述: Response运行流程设置响应行设置响应头一个小demo 实现刷新页面累加设置字符编码解决中文乱码问题重定向 redirect request转发重定向和转发

HttpResponse 讲解

HttpServletResponse概述:

在创建Servlet时会覆盖service()方法，或doGet()/doPost(),这些方法都有两个参数，一个为代表请求的request和代表响应response。service方法中的response的类型是ServletResponse，而doGet/doPost方法的response的类型是HttpServletResponse，HttpServletResponse是ServletResponse的子接口，功能和方法更加强大。

Response运行流程

响应头有很多这里只介绍常用的。

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在浏览器可以按F12 抓包看响应头、请求头、具体的可以再查。

设置响应行

设置响应的状态码

/**
 * @Author: crush
 * @Date: 2021-05-09 19:35
 * version 1.0
 */
@WebServlet("/test3")
public class HttpResponseTest3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        System.out.println("设置状态码,前台通过判断状态码，来判断请求是否成功");
        resp.setStatus(404);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

测试

在这里插入图片描述

设置响应头

刷新跳转页面

/**
 * @Author: crush
 * @Date: 2021-05-09 19:35
 * version 1.0
 */
@WebServlet("/test4")
public class HttpResponseTest4 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 设置响应头 每1秒自动刷新
        System.out.println("设置响应头 每1秒自动刷新");
        resp.setHeader("Refresh", "1");
        //定时跳转 3秒后将自动跳转
//        resp.setHeader("Refresh","3;URL=hello.jsp");
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

测试

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一个小demo 实现刷新页面累加

/**
 * response
 * @author Adimi
 */
@WebServlet("/test4")
public class ResponseTest4 extends HttpServlet {
    private static Integer id=1;
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setHeader("Refresh","1");
        PrintWriter writer = response.getWriter();
        id++;
        writer.print("id==>"+id);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

设置字符编码解决中文乱码问题

/**
 * @Author: crush
 * @Date: 2021-05-09 19:35
 * version 1.0
 */
@WebServlet("/test1")
public class HttpResponseTest1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 解决中文乱码问题
        // 设置响应头
        // 设置字符编码 resp.setCharacterEncoding("UTF-8");
        // 设置响应内容以什么格式展示到页面 什么编码格式 包含了设置字符编码
        resp.setContentType("text/html;charset=utf-8");
        PrintWriter writer = resp.getWriter();
        writer.print("中国,你好！！！");
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

测试

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重定向 redirect

/**
 * 重定向
 * @Author: crush
 * @Date: 2021-05-09 19:35
 * version 1.0
 */
@WebServlet("/test5")
public class HttpResponseTest5 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.sendRedirect("hello.jsp");
//        resp.setHeader("location","www.baidu.com"); 通过设置响应头转发
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

request转发

/**
 * 重定向
 * @Author: crush
 * @Date: 2021-05-09 19:35
 * version 1.0
 */
@WebServlet("/test5")
public class HttpResponseTest5 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        resp.sendRedirect("hello.jsp");
        req.getRequestDispatcher("hello.jsp").forward(req,resp);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

重定向和转发的区别

文件下载

获取路径资源

String path=this.getServletContext().getRealPath("WEB-INF\\classes\\8.jpg");

读取资源

FileInputStream fileInputStream=new FileInputStream(path);

获取到文件名，路径在电脑上保存的形式是 \ \

String fileName=path.substring(path.lastIndexOf("\\")+1);

设置消息头告诉浏览器，我要下载1.png这个图片设置编码

resp.setHeader("Content-Disposition", "attachment; filename=" + URLEncoder.encode(fileName, "UTF-8"));

把读取到的内容回送给浏览器

 int len=0;
byte[] bytes=new byte[1024];
// ServletOutputStream 提供用于将二进制数据发送到客户端的输出流
ServletOutputStream servletOutputStream=resp.getOutputStream();
while((len=fileInputStream.read(bytes))>0) {
    servletOutputStream.write(bytes,0,len);
}

关闭资源

servletOutputStream.close();
        fileInputStream.close();

注：8.jpg 放在我的resources 文件夹下但是这里需要写的是编译完8.jpg存放的位置

具体代码

/**
 * @Author: crush
 * @Date: 2021-05-09 19:40
 * version 1.0
 */
@WebServlet("/down")
public class ResponseDownFile extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //获取路径资源
        String path=this.getServletContext().getRealPath("WEB-INF\\classes\\8.jpg");
        //读取资源
        FileInputStream fileInputStream=new FileInputStream(path);
        //获取到文件名，路径在电脑上保存的形式是\\
        String fileName=path.substring(path.lastIndexOf("\\")+1);
        //设置消息头告诉浏览器，我要下载1.png这个图片
        // 该方式文件名为中文时会乱码
        //防止中文乱码
        resp.setHeader("Content-Disposition", "attachment; filename=" + URLEncoder.encode(fileName, "UTF-8"));
        //把读取到的内容回送给浏览器
        int len=0;
        byte[] bytes=new byte[1024];
        ServletOutputStream servletOutputStream=resp.getOutputStream();
        while((len=fileInputStream.read(bytes))>0) {
            servletOutputStream.write(bytes,0,len);
        }
        // 关闭资源
        servletOutputStream.close();
        fileInputStream.close();
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

HttpRequest 讲解

HttpServletRequest概述

我们在创建Servlet时会覆盖service()方法，或doGet()/doPost(),这些方法都有两个参数，一个为代表请求的request和代表响应response。service（）方法中写了根据请求方式的不同调用doget()和dopost().

service方法中的request的类型是ServletRequest，而doGet/doPost方法的request类型HttpServletRequest，HttpServletRequest是ServletRequest的子接口，功能和方法更加强大.

Request 运行流程

获取请求携带的参数

/**
 * @Author: crush
 * @Date: 2021-05-11 16:52
 * version 1.0
 */
@WebServlet("/request1")
public class RequestTest1 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 这里是请求的参数名  必须是同名的 
        String username = req.getParameter("username"); 
        String password = req.getParameter("password");
        PrintWriter writer = resp.getWriter();
        writer.print("<h1>"+username+":"+password+"</h1>");
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

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获取多个参数的值

  @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 设置请求的编码  不然会乱码
        req.setCharacterEncoding("utf-8");
        Enumeration<String>  names = req.getParameterNames();
        while (names.hasMoreElements()) {
            String name = (String) names.nextElement();
            String[]  values = req.getParameterValues(name);
            System.out.println(name+":"+ Arrays.toString(values));
        }
    }

获得请求行的信息

/**
 * @Author: crush
 * @Date: 2021-05-11 16:52
 * version 1.0
 */
@WebServlet("/request3")
public class RequestTest3 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 获得请求的url
        StringBuffer requestURL = req.getRequestURL();
        System.out.println("请求的URL===>"+requestURL);
        // 获得请求的Servlet的路径
        String path = req.getServletPath();
        System.out.println("请求的Servlet的路径===>"+path);
        //返回发出此请求的HTTP方法的名称，例如GET，POST或PUT
        String method = req.getMethod();
        System.out.println("返回发出此请求的HTTP方法的名称==>"+method);
        //返回发送请求的客户端或最后一个代理的Internet协议（IP）地址
        String remoteAddr = req.getRemoteAddr();
        System.out.println("remoteAddr==>"+remoteAddr);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

request实现转发

/**
 * @Author: crush
 * @Date: 2021-05-11 16:52
 * version 1.0
 */
@WebServlet("/request2")
public class RequestTest2 extends HttpServlet {
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // 访问request2 转发到 request4去
        req.getRequestDispatcher("/request4").forward(req,resp);
    }
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doGet(req, resp);
    }
}

request是一个域对象

request对象也是一个存储数据的区域对象，所以也具有如下方法：

setAttribute(String name, Object o)

getAttribute(String name)

removeAttribute(String name)

ServletContext 作用域：

创建：启动web应用程序的时候创建

销毁：关闭web应用程序的时候销毁

域的作用范围：整个web应用的启动周期

request作用域：

创建：访问时创建request

销毁：响应结束request销毁

域的作用范围：一次请求中

总结

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