javaweb 5、HttpServletResponse
HttpServletResponse
web服务器接收到客户端的http请求，针对这个请求，分别创建一个代表请求的HttpServletRequest对象，代表响应的一个HttpServletResponse
- 如果要获取客户端请求过来的参数：找HttpServletRequest
- 如果要给客户端响应一些信息：找HttpServletResponse
简单分类
负责向浏览器发送数据的方法
ServletOutputStream getOutputStream() throws IOException;
Printwriter getwriter() throws IOException;
负责向浏览器发送响应头的方法
void setCharacterEncoding(String var1);
void setContentLength(int var1);
void setContentLengthLong(long var1);
void setContentType(String var1);
void setDateHeader(String var1, long var2);
void addDateHeader(String var1, long var2);
void setHeader(String var1, String var2);
void addHeader(String var1, String var2);
void setIntHeader(String var1, int var2);
void addIntHeader(String var1, int var2);
响应的状态码
int SC_CONTINUE = 100;
int SC_SWITCHING_PROTOCOLS = 101;
int SC_OK = 200;
int SC_CREATED = 201;
int SC_ACCEPTED = 202;
int SC_NON_AUTHORITATIVE_INFORMATION = 203;
int SC_NO_CONTENT = 204;
int SC_RESET_CONTENT = 205;
int SC_PARTIAL_CONTENT = 206;
int SC_MULTIPLE_CHOICES = 300;
int SC_MOVED_PERMANENTLY = 301;
int SC_MOVED_TEMPORARILY = 302;
int SC_FOUND = 302;
int SC_SEE_OTHER = 303;
int SC_NOT_MODIFIED = 304;
int SC_USE_PROXY = 305;
int SC_TEMPORARY_REDIRECT = 307;
int SC_BAD_REQUEST = 400;
int SC_UNAUTHORIZED = 401;
int SC_PAYMENT_REQUIRED = 402;
int SC_FORBIDDEN = 403;
int SC_NOT_FOUND = 404;
int SC_METHOD_NOT_ALLOWED = 405;
int SC_NOT_ACCEPTABLE = 406;
int SC_PROXY_AUTHENTICATION_REQUIRED = 407;
int SC_REQUEST_TIMEOUT = 408;
int SC_CONFLICT = 409;
int SC_GONE = 410;
int SC_LENGTH_REQUIRED = 411;
int SC_PRECONDITION_FAILED = 412;
int SC_REQUEST_ENTITY_TOO_LARGE = 413;
int SC_REQUEST_URI_TOO_LONG = 414;
int SC_UNSUPPORTED_MEDIA_TYPE = 415;
int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;
int SC_EXPECTATION_FAILED = 417;
int SC_INTERNAL_SERVER_ERROR = 500;
int SC_NOT_IMPLEMENTED = 501;
int SC_BAD_GATEWAY = 502;
int SC_SERVICE_UNAVAILABLE = 503;
int SC_GATEWAY_TIMEOUT = 504;
int SC_HTTP_VERSION_NOT_SUPPORTED = 505;
常见应用
-
向浏览器输出信息
-
下载文件
- 要获取下载文件的路径
- 下载文件的文件名
- 设置想办法让浏览器能够支持下载我们需要的东西
- 获取下载文件的输入流
- 创建缓冲区
- 获取OutputStream对象
- 将FileOutputStream流写到buffer缓冲区
- 使用OutputStream将缓冲区中的数据输出到客户端
建一个web项目：response
补全java、resource目录
更新web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://jakarta.ee/xml/ns/jakartaee
https://jakarta.ee/xml/ns/jakartaee/web-app_5_0.xsd"
version="5.0"
metadata-complete="true">
</web-app>
在main/java/com.binzaza.servlet目录下创建java文件 FileServlet.java
public class FileServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// 1. 要获取下载文件的路径
String realPath = "D:\\IdeaProjects\\javaweb-02-servleb\\response\\src\\main\\resources\\1.jpg";
System.out.println("下载文件的路径："+realPath);
// 2. 下载文件的文件名
String fileName = realPath.substring(realPath.lastIndexOf("\\")+1);
// 3. 设置想办法让浏览器能够支持(Content-Disposition)下载我们需要的东西,中文文件名URLEncoder.encode(fileName,"UTF-8")
resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"UTF-8"));
// 4. 获取下载文件的输入流
FileInputStream in = new FileInputStream(realPath);
// 5. 创建缓冲区
int len = 0;
byte[] buffer = new byte[1024];
// 6. 获取OutputStream对象
ServletOutputStream out = resp.getOutputStream();
// 7. 将FileOutputStream流写到buffer缓冲区,使用OutputStream将缓冲区中的数据输出到客户端
while ((in.read(buffer)>0)){
out.write(buffer,0,len);
}
in.close();
out.close();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
配置路由web.xml
<servlet>
<servlet-name>filedown</servlet-name>
<servlet-class>com.binzaza.servlet.FileServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>filedown</servlet-name>
<url-pattern>/down</url-pattern>
</servlet-mapping>
启动tomcat
访问：http://localhost:8080/r/down
验证码功能
验证怎么实现
- 前端实现
- 后端实现，需要用到java的图片类，生成一个图片
创建一个java类ImageServlet.java
public class ImageServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// 如何让浏览器5s刷新一次
resp.setHeader("refresh","3");
// 在内存中创建一个图片
BufferedImage image = new BufferedImage(80,20,BufferedImage.TYPE_INT_ARGB);
// 得到图片
Graphics2D g = (Graphics2D) image.getGraphics(); // 比
// 设置图片的背景颜色
g.setColor(Color.white);
g.fillRect(0,0,80,20);
// 给图片写数据
g.setColor(Color.BLUE);
g.setFont(new Font(null,Font.BOLD,20));
g.drawString(makeNum(),0,20);
// 告诉浏览器，这个请求用图片的请求方式打开
resp.setContentType("image/jpeg");
// 网络存在缓存，不然浏览器缓存
resp.setDateHeader("expires",-1);
resp.setHeader("Cache-Control","no-cache");
resp.setHeader("Pragma","no-cache");
// 把图片写给浏览器
ImageIO.write(image, "jpg", resp.getOutputStream());
}
// 生成随机数
private String makeNum(){
Random random = new Random();
String num = random.nextInt(99999999)+"";
StringBuffer sb = new StringBuffer();
for (int i = 0;i<7-num.length();i++){
sb.append("0");
}
String s = sb.toString()+num;
return num;
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
编辑路由
<servlet>
<servlet-name>image</servlet-name>
<servlet-class>com.binzaza.servlet.ImageServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>image</servlet-name>
<url-pattern>/img</url-pattern>
</servlet-mapping>
启动tomcat
访问：http://localhost:8080/r/img
实现重定向
一个web资源收到客户端请求后，他会通知客户端去访问另外一个web资源，这个过程叫做重定向
常见场景：
- 用户登录
void sendRedirect(String var1) throws IOException;
创建RedirectServlet.java
public class RedirectServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
/*
resp.setHeader("Location","/r/img");
resp.setStatus(302);
*/
resp.sendRedirect("/r/img"); // 重定向
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
设置路由web.xml
<servlet>
<servlet-name>Redirect</servlet-name>
<servlet-class>com.binzaza.servlet.RedirectServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Redirect</servlet-name>
<url-pattern>/red</url-pattern>
</servlet-mapping>
启动Tomcat
访问：http://localhost:8080/r/red
面试题
请你聊聊重定向和转发的区别？
- 相同点
- 页面都会实现跳转
- 不同点
- 请求转发的时候，url不会发生不变化
- 重定向的时候，url地址栏会发生变化
创建文件RequestText.java
public class RequestText extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// 处理请求
String username = req.getParameter("username");
String password = req.getParameter("password");
System.out.println(username+":"+password);
// 重定向的时候一定要注意路径的问题，否则404
resp.sendRedirect("/r/success.jsp");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
修改index.jsp
<%@ page contentType="text/html; charset=UTF-8"%>
<html>
<body>
<h2>Hello World!</h2>
<!--这里提交的路径，需要寻找到项目的路径-->
<%--${pageContext.request.contextPath}代表当前的项目--%>
<form action="${pageContext.request.contextPath}/login" method="get">
用户名：<input type="text" name="username"> <br>
密码：<input type="password" name="password"> <br>
<input type="submit">
</form>
</body>
</html>
创建重定向跳转页面success.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<h1>Success</h1>
</body>
</html>
配置路由web.xml
<servlet>
<servlet-name>request</servlet-name>
<servlet-class>com.binzaza.servlet.RequestText</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>request</servlet-name>
<url-pattern>/login</url-pattern>
</servlet-mapping>
启动Tomcat
