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。