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2019年7月14日。
这是我学习JavaWeb的第二天。 这一天,我学到了以下的知识。Servlet接口被SUN公司定义了两个默认实现类,分别为:GenericServlet、HttpServlet
package servlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;public class ServletTest01 extends javax.servlet.http.HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws javax.servlet.ServletException, IOException { } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws javax.servlet.ServletException, IOException { }}
在web.xml文件中,会多出一个Servlet标签,代码如下所示:
ServletTest01 servlet.ServletTest01 ServletTest01 /test01
这样,一个Servlet就创建完成了。
将这个请求,转换到另一个地址。
例如,我们请求 却跳转到了 百度的首页,代码如下(ServletTest01对应的请求URL在web.xml提前设置好):import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;import java.io.PrintWriter;@WebServlet(name = "ServletTest01")public class ServletTest01 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.sendRedirect("https://www.baidu.com/"); }}
Web容器在启动时,它会为每个WEB应用程序都创建一个对应的ServletContext对象,它代表当前的WEB应用。
ServletContext类,作用如下:
假设有一个名为ServletDemo01的Servlet,要传输一个键为name而值为abc的数据给ServletDemo02,代码如下:
import javax.servlet.ServletContext;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;public class ServletDemo01 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws javax.servlet.ServletException, IOException { doGet(request,response); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws javax.servlet.ServletException, IOException { // 通过servlet对象,可以获取一个servletContext; response.setCharacterEncoding("gbk"); ServletContext servletContext = this.getServletContext(); String username = "abc"; // 可以通过JDBC去读取; // setAttribute:设置一个属性;(属性名,属性值) servletContext.setAttribute("name",username); response.getWriter().print("设置信息成功!" + username); }}
import javax.servlet.ServletContext;import javax.servlet.ServletException;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.IOException;public class ServletDemo02 extends HttpServlet { protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { ServletContext servletContext = this.getServletContext(); String name = (String) servletContext.getAttribute("name"); response.setCharacterEncoding("gbk"); response.getWriter().print("获取到的信息为:" + name ); } protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request,response); }}
示例图如下:
1.在项目src目录下新建resources目录,在该目录下新建一个properties文件,如下所示:
driver=com.mysql.jdbc.Driverusername=rootpassword=123456url=jdbc:mysql://localhost:3306/smbms
2.编写Servlet类
import javax.servlet.ServletException;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.util.Properties;//读取properties配置文件public class ServletDemo03 extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doPost(req,resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //读取配置文件 //1.获得配置文件的路径 String realPath = this.getServletContext().getRealPath("/WEB-INF/classes/resources/database.properties"); System.out.println("取得的路径为:"+realPath); Properties properties = new Properties(); FileInputStream is = new FileInputStream(realPath); properties.load(is);//把文件流加载到配置文件的对象中; String driver = properties.getProperty("driver"); String username = properties.getProperty("username"); String password = properties.getProperty("password"); String url = properties.getProperty("url"); //响应到网页 resp.getWriter().println(driver); resp.getWriter().println(username); resp.getWriter().println(password); resp.getWriter().println(url); //======================================= System.out.println(driver); System.out.println(username); System.out.println(password); System.out.println(url); }}
3.配置web.xml
Demo03 com.servlet.ServletDemo03 Demo03 /ccc
4.访问查看
在页面的链接栏中输入 localhost:8080/demo02/ccc,可以查看到如下页面:设置一个六位数的随机数作为验证码,每次刷新时验证码都会发生变换,代码如下:
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.Map;//验证码public class ServletDemo04 extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doPost(req,resp); } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { //resp.getWriter().println(newRandom()); //自动刷新网页 resp.setHeader("refresh","2"); //验证码是一个图片 , 我们需要制作一个图片 BufferedImage image = new BufferedImage(100,30,BufferedImage.TYPE_3BYTE_BGR); //图片写入一些东西 Graphics2D graphics = image.createGraphics(); graphics.setColor(Color.red); String num = String.valueOf(newRandom()); graphics.drawString(num,10,10); //想办法让浏览器知道我们给的是一张图片 resp.setContentType("image/jpg"); //让网站去打开图片 ImageIO.write(image,"jpg",resp.getOutputStream()); } //生成随机数 public int newRandom(){ int num = (int)(Math.random()*9+1)*100000; return num; } /* @Test public void test(){ ServletDemo04 servletDemo04 = new ServletDemo04(); for (int j = 0; j < 100; j++) { int i = servletDemo04.newRandom(); System.out.println(i); } } */}
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