标签:JavaWeb int Servlet resp SC import servlet javax
1、servlet简介
- Servlet是sun公司开发动态web的一门技术
- sun公司提供了一个接口叫做Servlet,如果你想开发一个Servlet程序,只需要完成两个步骤:
- 编写一个类,继承HttpServlet类
- 把开发好的Java类部署到web服务器中
把实现了Servlet接口的Java程序叫做Servlet
2、HelloServlet
2.1 编写servlet
package com.zjb.servlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class HelloServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
PrintWriter writer = resp.getWriter();
writer.print("HelloServlet");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
2.2 编写servlet映射
我们写的是java程序,但是要通过浏览器访问,而浏览器需要连接web服务器,所以我们需要在web服务中注册我们写的servlet,还需要给他一个浏览器能够访问的路径。
<!--注册servlet-->
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.zjb.servlet.HelloServlet</servlet-class>
</servlet>
<!--servlet的请求路径-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>helloServlet</url-pattern>
</servlet-mapping>
3.servlet原理
Servlet是由web服务器调用,web在收到浏览器请求之后,
4. Mapping问题
4.1、 一个Servlet可以指定一个映射路径
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/helloServlet</url-pattern>
</servlet-mapping>
4.2、一个Servlet可以指定多个映射路径
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/helloServlet</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/helloServlet1</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/helloServlet2</url-pattern>
</servlet-mapping>
4.3、一个Servlet可以指定通用映射路径
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/helloServlet/*</url-pattern>
</servlet-mapping>
4.4、 默认请求路径
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
4.5、指定一些后缀或者前缀等等
<!--使用自定义后缀实现请求映射 注意点:*前面不能加项目映射的路径-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>
4.6.优先级问题
指定了固有的映射路径优先级最高,如果找不到就会走默认的处理请求;
做个验证:
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
version="3.1"
metadata-complete="true">
<!--注册servlet-->
<servlet>
<servlet-name>hello</servlet-name>
<servlet-class>com.zjb.servlet.HelloServlet</servlet-class>
</servlet>
<servlet>
<servlet-name>error</servlet-name>
<servlet-class>com.zjb.servlet.ErrorServlet</servlet-class>
</servlet>
<!--servlet的请求路径-->
<servlet-mapping>
<servlet-name>hello</servlet-name>
<url-pattern>/helloServlet</url-pattern>
</servlet-mapping>
<!--404 : 映射路径给默认的映射路径-->
<servlet-mapping>
<servlet-name>error</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
</web-app>
package com.zjb.servlet;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class ErrorServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
resp.setContentType("text/html");
resp.setCharacterEncoding("utf-8");
PrintWriter writer = resp.getWriter();
writer.print("<h1>404</h1>");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
启动访问,发现当访问路径是/helloServlet时,依然可以正常访问。
5.ServletContext对象(获取上下文)
web容器在启动的时候,它会为每个web程序都创建一个对应的ServletContext对象,它代表了当前的web应用。
5.1.共享数据
在一个servlet中保存的数据,可以在另外一个servlet中拿到。
package com.zjb.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class ServletContextServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//获取Servlet上下文
ServletContext servletContext = this.getServletContext();
String username = "上下文";
servletContext.setAttribute("username",username);
System.out.println("向ServletContext对象中存入用户名:"+username);
}
}
package com.zjb.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
public class GetServletContextServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext servletContext = this.getServletContext();
String username = (String)servletContext.getAttribute("username");
resp.setContentType("text/html");
resp.setCharacterEncoding("utf-8");
PrintWriter writer = resp.getWriter();
writer.print("<h1>用户名:"+username+"</h1>");
}
}
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
version="3.1"
metadata-complete="true">
<!--注册servlet-->
<servlet>
<servlet-name>setContext</servlet-name>
<servlet-class>com.zjb.servlet.ServletContextServlet</servlet-class>
</servlet>
<servlet>
<servlet-name>getContext</servlet-name>
<servlet-class>com.zjb.servlet.GetServletContextServlet</servlet-class>
</servlet>
<!--servlet的请求路径-->
<servlet-mapping>
<servlet-name>setContext</servlet-name>
<url-pattern>/setC</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>getContext</servlet-name>
<url-pattern>/getC</url-pattern>
</servlet-mapping>
</web-app>
启动并访问
5.2. 获取初始化参数
<!--配置一些web应用的初始化参数-->
<context-param>
<param-name>url</param-name>
<param-value>jdbc:mysql://localhost:3306/demo</param-value>
</context-param>
package com.zjb.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
/**
* 获取初始化参数
**/
public class GetInitParamServlet extends HttpServlet{
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext servletContext = this.getServletContext();
String url = servletContext.getInitParameter("url");
resp.setContentType("text/html");
resp.setCharacterEncoding("utf-8");
PrintWriter writer = resp.getWriter();
writer.print("<h1>数据库连接路径:"+url+"</h1>");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
5.3.请求转发
package com.zjb.servlet;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
/**
* ServletContext 实现请求转发
*/
public class GetRequestDispatcherServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext servletContext = this.getServletContext();
//转发的路径
RequestDispatcher requestDispatcher = servletContext.getRequestDispatcher("/getIp");
//调用forward方法实现请求转发
requestDispatcher.forward(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
转发的时候路径是不会发生改变的。
5.4.读取资源文件
Properties
- Servle在java目录下新建properties文件
- 在resources目录下新建properties文件
发现:都被打包到了同一个路径下:classes,我们俗称这个路径为类路径classpath;
package com.zjb.servlet;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.InputStream;
import java.io.PrintWriter;
import java.util.Properties;
/***
* ServletContext 实现读取资源文件
*/
public class GetResourceServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
ServletContext servletContext = this.getServletContext();
InputStream resourceAsStream = servletContext.getResourceAsStream("/WEB-INF/classes/db.properties");
Properties properties = new Properties();
properties.load(resourceAsStream);
String username = properties.getProperty("username");
String password = properties.getProperty("password");
resp.setContentType("text/html");
resp.setCharacterEncoding("utf-8");
PrintWriter writer = resp.getWriter();
writer.print("<h1>用户名:"+username+",密码:"+password+"</h1>");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
6.HttpServletRequest
HttpServletRequest代表客户端的请求,用户通过http协议访问服务器,http请求中的所有信息会被封装到HttpServletRequest,通过这个HttpServletRequest的方法,获得客户端的所有信息。
6.1 获取前端传递的参数
String getParameter(String var1);
String[] getParameterValues(String var1);
6.2 请求转发
package com.zjb.request;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.Arrays;
/**
* HttpServletRequest 请求转发
*/
public class GetParamServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
req.setCharacterEncoding("utf-8");
resp.setCharacterEncoding("utf-8");
String username = req.getParameter("username");
String password = req.getParameter("password");
System.out.println(username+":"+password);
String[] hobbies = req.getParameterValues("hobbies");
System.out.println("hobbies:"+Arrays.toString(hobbies));
//请求转发
req.getRequestDispatcher("/success.jsp").forward(req,resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
7.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,代表响应一个HttpServletResponse;
- 如果要获取客户端请求过来的参数:找HttpServletRequest
- 如果要获取客户端响应的一些信息:找HttpServletResponse
7.1. 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);
负责向浏览器发送响应状态码的方法
void setStatus(int var1);
响应状态码的常量
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;
7.2 常见应用
1. 向浏览器输出信息
2.下载文件
package com.zjb.response;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.FileInputStream;
import java.io.IOException;
import java.net.URLEncoder;
/**
* HttpServletResponse 实现下载文件
* 实现步骤:
* 1.要获取下载文件的路径
* 2.下载的文件名是什么
* 3.想办法设置让浏览器能够支持下载我们需要的东西
* 4.获取下载文件的输入流
* 5.创建缓冲区
* 6.获取OutPutStream对象
* 7.将FileOutPutStream流写入到buffer缓冲区,使用OutPutStream将缓冲区中的数据输出到客户端
*/
public class DownloadResponseServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//获取要下载的文件路径
String realPath = "C:\\lesson\\learn-javaweb\\servlet-01\\target\\classes\\1.jpg";
System.out.println("下载文件的路径:"+realPath);
//下载文件的文件名
String fileName = realPath.substring(realPath.lastIndexOf("\\") + 1);
System.out.println("文件名:"+fileName);
//设置让浏览器能够支持下载我们需要的东西,使用URLEncoder.encode来解决文件名是中文乱码
resp.setHeader("Content-Disposition","attachment;filename="+ URLEncoder.encode(fileName,"UTF-8"));
//获取下载文件的输入流
FileInputStream fileInputStream = new FileInputStream(realPath);
//创建缓冲区
int len = 0;
byte[] buffer = new byte[1024];
//获取OutPutStream对象
ServletOutputStream outputStream = resp.getOutputStream();
//将FileOutPutStream流写入到buffer缓冲区,使用OutPutStream将缓冲区中的数据输出到客户端
while((len = fileInputStream.read(buffer))>0){
outputStream.write(buffer,0,len);
}
fileInputStream.close();
outputStream.close();
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req,resp);
}
}
3. 验证码功能
package com.zjb.response;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
/**
* HttpServletResponse 实现验证码功能
*/
public class ImageServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//如何让浏览器3秒自动刷新一次
resp.setHeader("refresh","3");
//在内存中创建一个图片
BufferedImage bufferedImage = new BufferedImage(80,20,BufferedImage.TYPE_INT_RGB);
//得到一个2D画笔
Graphics2D graphics = (Graphics2D)bufferedImage.getGraphics();
//设置图片的背景颜色
graphics.setColor(Color.white);
graphics.fillRect(0,0,80,20);
//给图片写数据
graphics.setColor(Color.BLUE);
graphics.setFont(new Font(null,Font.BOLD,20));
graphics.drawString(makeRandomNum(),0,20);
//告诉浏览器,这个请求用图片的方式打开
resp.setContentType("image/jpeg");
//网站存在缓存,不让浏览器缓存
resp.setDateHeader("expires",-1);
resp.setHeader("Cache-Control","no-cache");
resp.setHeader("Prama","no-cache");
//把图片写给浏览器
ImageIO.write(bufferedImage,"jpg",resp.getOutputStream());
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
public String makeRandomNum(){
Random random = new Random();
String num = String.valueOf(random.nextInt(99999999));
StringBuffer sb = new StringBuffer();
for (int i = 0; i < 7-num.length(); i++) {
sb.append("0");
}
return sb.toString() + num;
}
}
4.response重定向(重点)
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,这个过程叫重定向。
void sendRedirect(String var1) throws IOException;
package com.zjb.response;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
/**
* HttpServletResponse 实现重定向
*/
public class RedirectServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("进入重定向方法");
/**
* 重定向的原理:
* resp.setHeader("location","/servlet/image");
* resp.setStatus(HttpServletResponse.SC_MOVED_TEMPORARILY);
* 就等价于 resp.sendRedirect("/servlet/image")
*/
//重定向的时候一定要注意路径问题
resp.sendRedirect(req.getContextPath()+"/image");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
我们发现路径发生了改变,并且状态码是302 。
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不会产生变化
- 重定向的时候,url地址栏会发生变化
常见场景:
- 用户登录
package com.zjb.response;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class LoginDemoServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("进入到该登录方法");
String username = req.getParameter("username");
String password = req.getParameter("password");
System.out.println(username+":"+password);
//重定向
resp.sendRedirect("/servlet/success.jsp");
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
}
index.jsp
<html>
<body>
<h2>Hello World!</h2>
<%-- ${pageContext.request.contextPath} 代表当前的项目--%>
<form action="${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>
success.jsp
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
<title>Title</title>
</head>
<body>
<h1>Success</h1>
</body>
</html>
标签:JavaWeb,int,Servlet,resp,SC,import,servlet,javax 来源: https://blog.csdn.net/qq_41910252/article/details/118497713
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