5.修改数据
5.1编写查询条件页面
修改单条数据的时候，首先是查询出单个数据的详细信息，然后根据实际需要部分修改或者全部修改。修改之后，数据会提交到数据库，数据库中保存更新以后的数据。
查询出单条数据的查询条件页面代码如下：
QueryToUpdate.html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html><head><title>QueryToUpdate.html</title><meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="this is my page"><meta http-equiv="content-type" content="text/html; charset=UTF-8"><!--<link rel="stylesheet" type="text/css" href="./styles.css">--></head><body><form name="f1" id="f1" action="/jdbc_servlet/servlet/QueryToUpdateServlet" method="post"><table border="0"><tr><td>请输入要修改的部门编号:</td><tr></tr><td><input type="text" name="id" ></td></tr><tr><td colspan="2" align="left"><input type="submit" value="提交"></td></tr></table></form></body> </html>
5.2 编写显示部门详细信息的Servlet
输入要修改的部门编号以后，进入根据部门编号查询部门信息的Servlet，把部门详细信息显示到页面中，一些不可以修改的字段可以设置成只读，这样就不会把这些数据修改了，该Servlet的代码如下：
QueryToUpdateServlet.java
package com.cn.update;import java.io.IOException; import java.io.PrintWriter; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException;import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;public class QueryToUpdateServlet extends HttpServlet {/*** Destruction of the servlet. <br>*/public void destroy() {super.destroy(); // Just puts "destroy" string in log// Put your code here }/*** The doGet method of the servlet. <br>** This method is called when a form has its tag value method equals to get.* * @param request the request send by the client to the server* @param response the response send by the server to the client* @throws ServletException if an error occurred* @throws IOException if an error occurred*/public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=gb2312");request.setCharacterEncoding("gb2312");PrintWriter out = response.getWriter();String id = request.getParameter("id");Connection con = null;PreparedStatement pstmt = null;ResultSet rs = null;try {Class.forName("com.mysql.jdbc.Driver");System.out.println("创建驱动成功！");con = DriverManager.getConnection("jdbc:mysql://localhost:3306/bank", "root", "1234");System.out.println("数据库连接成功！");String sql = "SELECT * FROM dept WHERE id=?";pstmt = con.prepareStatement(sql);pstmt.setString(1, id);rs = pstmt.executeQuery();} catch (ClassNotFoundException e) {// TODO Auto-generated catch block e.printStackTrace();} catch (SQLException e) {// TODO Auto-generated catch block e.printStackTrace();}//显示单个部门的信息out.println("<html>"+ "<head><title>显示单个部门信息</title></head>"+ "<body>");out.println("<h1>显示单个部门信息</h1><br><br>");out.print("<form action='/jdbc_servlet/servlet/UpdateDeptServlet' method='post'>");try {while(rs.next()){out.println("部门编号：");out.print("<br>");//在文本框中显示部门编号，设置成只读out.println("<input type='text' name='id' readonly='true' value=");out.println(rs.getString(1).toString());out.print(">");out.print("<br>");out.println("部门名称：");out.print("<br>");//在文本框中显示部门名称out.println("<input type='text' name='d_name' value=");out.println(rs.getString(2).toString());out.print(">");out.print("<br>");out.println("部门地址：");out.print("<br>");//在文本框中显示部门地址out.println("<input type='text' name='address' value=");out.println(rs.getString(3).toString());out.print(">");out.print("<br>");out.println("部门人数：");out.print("<br>");//在文本框中显示部门人数out.println("<input type='text' name='empnumber' value=");out.println(rs.getString(4).toString());out.print(">");out.print("<br>");//提交按钮out.print("<input type='submit' value='Submit'>");out.print("</form>");}} catch (SQLException e) {// TODO Auto-generated catch block e.printStackTrace();}out.flush();out.close();}/*** The doPost method of the servlet. <br>** This method is called when a form has its tag value method equals to post.* * @param request the request send by the client to the server* @param response the response send by the server to the client* @throws ServletException if an error occurred* @throws IOException if an error occurred*/public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=gb2312");request.setCharacterEncoding("gb2312");PrintWriter out = response.getWriter();this.doGet(request, response);out.flush();out.close();}/*** Initialization of the servlet. <br>** @throws ServletException if an error occurs*/public void init() throws ServletException {// Put your code here }}
5.3编写处理修改操作的Servlet
在UpdateDeptServlet中，修改数据以后，显示出数据库表中的全部信息。UpdateDeptServlet的代码如下：
UpdateDeptServlet.java
package com.cn.update;import java.io.IOException; import java.io.PrintWriter; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement;import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;public class UpdateDeptServlet extends HttpServlet {/*** The doGet method of the servlet. <br>** This method is called when a form has its tag value method equals to get.* * @param request the request send by the client to the server* @param response the response send by the server to the client* @throws ServletException if an error occurred* @throws IOException if an error occurred*/public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html");PrintWriter out = response.getWriter();this.doPost(request, response);out.flush();out.close();}/*** The doPost method of the servlet. <br>** This method is called when a form has its tag value method equals to post.* * @param request the request send by the client to the server* @param response the response send by the server to the client* @throws ServletException if an error occurred* @throws IOException if an error occurred*/public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=gb2312");request.setCharacterEncoding("gb2312");PrintWriter out = response.getWriter();Connection con = null;PreparedStatement ps = null;ResultSet rs = null;Statement sta = null;String id = request.getParameter("id");String address = request.getParameter("address");int empnumber = Integer.parseInt(request.getParameter("empnumber"));String d_name = request.getParameter("d_name");try {Class.forName("com.mysql.jdbc.Driver");System.out.println("创建驱动成功！");con = DriverManager.getConnection("jdbc:mysql://localhost:3306/bank", "root", "1234");System.out.println("数据库连接成功！");String sql = "UPDATE dept SET id=?,address=?,empnumber=?,d_name=? WHERE id=?";ps = con.prepareStatement(sql);//下面设置修改的数据值ps.setString(1, id);ps.setString(2, address);ps.setInt(3, empnumber);ps.setString(4, d_name);ps.setString(5, id);ps.executeUpdate();System.out.println("修改成功！");/** 添加成功后，显示全部信息*/sta = con.createStatement();rs = sta.executeQuery("SELECT * FROM dept");//在页面中显示表中的所有信息 out.println("<html>"+"<head><title>部门表信息</title></head>"+"<body>");out.println("<h1>部门表信息:</h1><br><br>");//循环遍历输出查询结果while(rs.next()){out.print("部门编号：");out.print(rs.getString(1)+"\t");out.print("部门名称：");out.print(rs.getString(2)+"\t");out.print("部门地址：");out.print(rs.getString(3)+"\t");out.print("部门人数：");out.print(rs.getString(4)+"\t");out.println("<br>");}out.print("</body></html>");out.close();} catch (ClassNotFoundException e) {// TODO Auto-generated catch block e.printStackTrace();} catch (SQLException e) {// TODO Auto-generated catch block e.printStackTrace();} out.flush();out.close();}/*** Initialization of the servlet. <br>** @throws ServletException if an error occurs*/public void init() throws ServletException {// Put your code here }}
6. 删除数据
删除数据时，要指定删除的条件，否则会把表中的所有数据删除。删除以后，被删除的数据在表中就不存在了。下面的例子是根据部门编号删除数据的例子。首先在页面中输入要删除的部门编号，输入要删除的部门编号的页面代码入下：
delete.html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html><head><title>delete.html</title><meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="this is my page"><meta http-equiv="content-type" content="text/html; charset=gb2312"><!--<link rel="stylesheet" type="text/css" href="./styles.css">--></head><body><form name="f1" id="f1" action="/jdbc_servlet/servlet/DeleteByIdServlet" method="post"><table border="0"><tr><td>请输入要删除的部门编号:</td><tr></tr><td><input type="text" name="id" ></td></tr><tr><td colspan="2" align="left"><input type="submit" value="删除"></td></tr></table></form></body> </html>
当输入删除条件后，单击【删除】按钮，会进入form表单指定的DeleteByIdServlet中，这是一个servlet，用来处理删除操作。DeleteByIdServlet中的代码如下：
DeleteByIdServlet.java
package com.cn.delete;import java.io.IOException; import java.io.PrintWriter; import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException;import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse;public class DeleteByIdServlet extends HttpServlet {/*** The doGet method of the servlet. <br>** This method is called when a form has its tag value method equals to get.* * @param request the request send by the client to the server* @param response the response send by the server to the client* @throws ServletException if an error occurred* @throws IOException if an error occurred*/public void doGet(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html");PrintWriter out = response.getWriter();this.doPost(request, response);out.flush();out.close();}/*** The doPost method of the servlet. <br>** This method is called when a form has its tag value method equals to post.* * @param request the request send by the client to the server* @param response the response send by the server to the client* @throws ServletException if an error occurred* @throws IOException if an error occurred*/public void doPost(HttpServletRequest request, HttpServletResponse response)throws ServletException, IOException {response.setContentType("text/html;charset=gb2312");request.setCharacterEncoding("gb2312");PrintWriter out = response.getWriter();String id = request.getParameter("id");Connection con = null; // ResultSet rs = null;PreparedStatement ps = null;try {Class.forName("com.mysql.jdbc.Driver");System.out.println("创建驱动成功！");con = DriverManager.getConnection("jdbc:mysql://localhost:3306/bank", "root", "1234");System.out.println("数据库连接成功！");String sql = "DELETE FROM dept WHERE id=?";ps = con.prepareStatement(sql);ps.setString(1, id);ps.executeUpdate();System.out.println("删除成功！");//显示结果信息out.println("<html><head><title>"+"删除部门表数据</title></head>"+"<body>");out.println("<h1>删除部门表数据成功！</h1>");out.print("</body></html>");} catch (ClassNotFoundException e) {// TODO Auto-generated catch block e.printStackTrace();} catch (SQLException e) {// TODO Auto-generated catch block e.printStackTrace();}out.flush();out.close();}/*** Initialization of the servlet. <br>** @throws ServletException if an error occurs*/public void init() throws ServletException {// Put your code here }}
在DeleteByIdServlet中，获得页面传递过来的部门编号，然后根据部门编号删除该编号对应的数据，删除成功则在页面中提示删除成功。
