声明:学了几天终于将增删改查的操作掌握了，也发现了一些问题，所以总结一下.
重点:操作数据库主要用的是SQL语句跟其他无关.
一:前提知识:PreparedStatement
PreperedStatement是Statement的子类，它的实例对象可以通过调用Connection.preparedStatement()方法获得，相对于Statement对象而言：PreperedStatement可以避免SQL注入的问题。
Statement会使数据库频繁编译SQL，可能造成数据库缓冲区溢出。PreparedStatement可对SQL进行预编译，从而提高数据库的执行效率。并且PreperedStatement对于sql中的参数，允许使用占位符的形式进行替换，简化sql语句的编写。
举例:
1 PreperedStatement mi = Connection.preparedStatement();
2 try{
3 i = mi.executeUpdate();
4 }catch(Exception e){
5 if(i != 1)
6 {
7 System.out.println("修改不成功");
8 }
9 }
二:实际例子:
1: 编写index.jsp文件通过JSTL中的<c:redirect>标签指向servlet
1 package com.ll;
2
3 import java.io.IOException;
4 import java.sql.*;
5 import java.util.ArrayList;
6 import java.util.List;
7
8 import javax.servlet.ServletException;
9 import javax.servlet.annotation.WebServlet;
10 import javax.servlet.http.HttpServlet;
11 import javax.servlet.http.HttpServletRequest;
12 import javax.servlet.http.HttpServletResponse;
13
14 import dao.Studentdao2;
15
16 /**
17 * Servlet implementation class GoodsServlet
18 */
19 @WebServlet("/GoodsServlet")
20 public class GoodsServlet extends HttpServlet {
21 private static final long serialVersionUID = 1L;
22
23 /**
24 * @see HttpServlet#HttpServlet()
25 */
26 public GoodsServlet() {
27 super();
28 // TODO Auto-generated constructor stub
29 }
30
31 /**
32 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
33 */
34 protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
35 // TODO Auto-generated method stub
36 String action = request.getParameter("action");
37 if(action.equals("zongjin")){
38
39 try {
40 query(request,response);
41 } catch (Exception e) {
42 // TODO Auto-generated catch block
43 e.printStackTrace();
44 }
45 }
46
47
48
49 }
50
51 /**
52 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
53 */
54 protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
55 // TODO Auto-generated method stub
56 }
57
58
59 public void query(HttpServletRequest request, HttpServletResponse response) throws Exception{
60 Studentdao2 conn = new Studentdao2();
61 String sql = "Select *from Student";
62
63 /*
64 //调用函数去向数据库中添加数据
65 String addsql = "于海-19-软件1501-男";
66 conn.addsql(addsql);
67 */
68
69
70 /*
71 //删除数据库中的数据
72 String strdelete = "Delete from Student Where 姓名 = ‘于海‘";
73 conn.deletesql(strdelete);
74 */
75
76 /*
77 //修改数据库中的数据
78 String update = "Update Student set 姓名=‘宗进‘ Where 姓名 = ‘小明‘ ";
79 conn.updateSql(update);
80 */
81
82
83 ResultSet rs =conn.executeQuery1(sql);//调用自制函数来接受查询的结果
84 List list = new ArrayList();
85 while(rs.next())
86 {
87 Student f = new Student();
88 //equals比较的结果为false是因为从数据库中返回的字符串为"宗进 "
89 f.setBanji(rs.getString("班级"));
90 f.setName(rs.getString("姓名"));
91 f.setSex(rs.getString("性别"));
92 f.setTime(rs.getString("年龄"));
93
94 list.add(f);
95
96 }
97
98 request.setAttribute("list", list);
99 request.getRequestDispatcher("sql2.jsp").forward(request, response);
100
101
102
103
104 }
105 public String cat(String str){
106 String[] arr = str.split(" ");
107 String s = arr[0];
108 return s;
109
110 }
111
112 }
3.Servlet的web.xml文件
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:jsp="http://java.sun.com/xml/ns/javaee/jsp" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0"> 3 <display-name>JSTL</display-name> 4 <welcome-file-list> 5 <welcome-file>index.html</welcome-file> 6 <welcome-file>index.htm</welcome-file> 7 <welcome-file>index.jsp</welcome-file> 8 <welcome-file>default.html</welcome-file> 9 <welcome-file>default.htm</welcome-file> 10 <welcome-file>default.jsp</welcome-file> 11 </welcome-file-list> 12 <jsp-config> 13 <taglib> 14 <taglib-uri>http://java.sun.com/jstl/fmt</taglib-uri> 15 <taglib-location>/WEB-INF/tld/fmt.tld</taglib-location> 16 </taglib> 17 <taglib> 18 <taglib-uri>http://java.sun.com/jstl/core</taglib-uri> 19 <taglib-location>/WEB-INF/tld/c.tld</taglib-location> 20 </taglib> 21 <taglib> 22 <taglib-uri>http://java.sun.com/jstl/sql</taglib-uri> 23 <taglib-location>/WEB-INF/tld/sql.tld</taglib-location> 24 </taglib> 25 <taglib> 26 <taglib-uri>http://java.sun.com/jstl/x</taglib-uri> 27 <taglib-location>/WEB-INF/tld/x.tld</taglib-location> 28 </taglib> 29 </jsp-config> 30 31 <servlet> 32 <servlet-name>GoodsServlet</servlet-name> 33 <servlet-class>com.ll.GoodsServlet</servlet-class> 34 </servlet> 35 36 <servlet-mapping> 37 <servlet-name>GoodsServlet</servlet-name> 38 <url-pattern>/com.ll.GoodsServlet</url-pattern> 39 </servlet-mapping> 40 47 48 </web-app>
4.创建一个用于连接数据库并且处理的类
1 package dao;
2
3 import java.io.InputStream;
4 import java.sql.Connection;
5 import java.sql.DriverManager;
6 import java.sql.PreparedStatement;
7 import java.sql.ResultSet;
8 import java.sql.SQLException;
9 import java.sql.Statement;
10 import java.util.Properties;
11
12 public class Studentdao2 {
13 public Connection conn = null;
14 public String url = null;
15 public Statement stmt = null;
16 public ResultSet rs = null;
17 public static String propFilename = "Studentdao2.properties";
18 private static Properties prop = new Properties();
19 private static String dbClassName = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
20 private static String dbUrl = "jdbc:sqlserver://localhost:1433;DatabaseName=StudentManagement";
21 private static String addSql = "insert into Student values(?,?,?,?)";
22 private static String updateSql = "update Student set 姓名=?,年龄=?,班级=?,性别=?";//用于整体修改数据库中的值
23 public Studentdao2(){
24 try{
25 // InputStream in = getClass().getResourceAsStream(propFilename);
26 // prop.load(in);
27 // dbClassName = prop.getProperty("DB_URL",dbUrl);
28 // dbUrl = prop.getProperty("DB_URL", dbUrl);
29 Class.forName(dbClassName);
30 conn = DriverManager.getConnection(dbUrl, "sa", "zongjin123");
31 if(conn != null)
32 {
33 System.out.println("连接成功");
34 }
35 else{
36 System.out.println("连接失败");
37 }
38 stmt = conn.createStatement();
39
40 }catch(Exception e){
41 e.printStackTrace();
42 }
43
44 }
45 public ResultSet executeQuery1(String sql) throws Exception {
46 // TODO Auto-generated method stub
47 this.rs = this.stmt.executeQuery(sql);
48 return this.rs;
49 }
50 public void addsql(String sql) throws Exception{
51 PreparedStatement add = conn.prepareStatement(addSql);
52 String[] shuju = sql.split("-");
53 System.out.println(shuju[0]);
54 add.setString(1, shuju[0]);
55 add.setString(2,shuju[1]);
56 add.setString(3,shuju[2]);
57 add.setString(4, shuju[3]);
58 add.executeUpdate();
59 add.close();
60 }
61 public void deletesql(String sql) throws Exception{
62 int i = 0;
63 PreparedStatement delete = conn.prepareStatement(sql);
64 try{
65 i = delete.executeUpdate();
66 }catch(Exception e){
67 if(i != 1)
68 {
69 System.out.println("删除失败");
70 }
71 }
72 delete.close();
73 }
74 public void updateSql(String sql)throws Exception
75 {
76 PreparedStatement update = conn.prepareStatement(sql);
77 //用于整体修改数据库中的值，但是一般直接用sq语句来进行操作数据库
78 //update.setString(2, str);
79 //String[] shuju = sql.split("-");
80 //System.out.println(shuju[0]);
81 //update.setString(1, shuju[0]);
82 //update.setString(2,shuju[1]);
83 //update.setString(3,shuju[2]);
84 //update.setString(4, shuju[3]);
85 update.executeUpdate();
86 update.close();
87 }
88
89 }
5.编写用于存储数据的student类
1 package com.ll;
2
3 public class Student {
4 private String name;
5 private String time;
6 private String banji;
7 private String sex;
8 public String getBanji() {
9 return banji;
10 }
11 public void setBanji(String banji) {
12 this.banji = banji;
13 }
14
15 public String getName() {
16 return name;
17 }
18 public void setName(String name) {
19 this.name = name;
20 }
21 public String getTime() {
22 return time;
23 }
24 public void setTime(String time) {
25 this.time = time;
26 }
27
28 public String getSex() {
29 return sex;
30 }
31 public void setSex(String sex) {
32 this.sex = sex;
33 }
34
35
36 }
6运行index.jsp文件来运行
时间： 2024-10-05 15:43:13