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JavaWeb入门:HttpResponse和HttpRequest详解

作者：宁在春　　发布时间：2022-09-05 16:44:31　

标签：java,Response,Request

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。

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

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

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

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);
}
}

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

来源：https://blog.csdn.net/weixin_45821811/article/details/116671015

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