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