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前面刚介绍了怎么连接数据库，也写了相应的模板，但是它的可维护性非常差，那么怎么解决这个问题呢？
首先写一个配置文件jdbc.properties
<span style="font-size:18px;">## MySQL driver=com.mysql.jdbc.Driver url=jdbc:mysql://localhost:3306/hncu?useUnicode=true&characterEncoding=UTF-8 username=root password=1234 ## Oracle #driver=oracle.jdbc.driver.OracleDriver #url=jdbc:oracle:thin:@192.168.31.12:1521:orcl #username=scott #password=tiger </span>
<span style="font-size:18px;">package cn.hncu.hibernate0;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.util.Properties;
public class ConnFactory {
private static Connection conn;
static {
try {
//读取配置文件
Properties p = new Properties();
p.load(ConnFactory.class.getClassLoader().getResourceAsStream("jdbc.properties"));
String driver = p.getProperty("driver");
String url = p.getProperty("url");
String username = p.getProperty("username");
String pwd = p.getProperty("password");
Class.forName(driver);
conn = DriverManager.getConnection(url,username,pwd);
System.out.println("已连接到数据库..."+conn);
} catch (Exception e) {
throw new RuntimeException("读取配置文件失败", e);
}
}
public static Connection getConn(){
return conn;
}
public static void main(String[] args) {
getConn();
}
}
</span>最后直接通过ConnFactory.getConn()获得。这要做的好处，当改变所要连接的数据库类型时，只需要修改配置文件中的内容即可。
<span style="font-size:18px;"><span style="white-space:pre"> </span>@Test
public void getXXXDemo() throws Exception{
Statement st = ConnFactory.getConn().createStatement();
String sql = "select * from book";
ResultSet rs = st.executeQuery(sql);
while(rs.next()){
Integer id = rs.getInt(1);//这里的1表示数据表中的第一列，下面同理
String name = rs.getString(2);
//Double price = (Double)rs.getObject(3);//出异常，因为内部是采用BigDecimal来处理
Double price = rs.getDouble(3);
Object dateTime = rs.getObject(4);//把日期和时间作为一个整体读取出来
System.out.println(id+","+name+","+price+","+dateTime);
String strDateTime = dateTime.toString();
System.out.println(strDateTime);
strDateTime = rs.getDate(4)+"--"+rs.getTime(4);//日期和时间可以单独获取
System.out.println(":::"+strDateTime);
}
ConnFactory.getConn().close();
}</span>注：对于自动增长列，删除之后再插入新记录，序号不会回头，继续往前增长。即中间会出现空号
1、executeQuery: 只能执行select语句
2、executeUpdate: 可以执行insert、delete和update语句，但不能执行select
3、execute:增删改查的4种(任意)语句都能执行。该方法若执行非select语句时返回false，执行select语句时返回true，且st对象会缓存该次查询的结果，我
们可通过ResultSet rs = st.getResultSet()来获得结果集
<span style="font-size:18px;"><span style="white-space:pre"> </span>@Test
public void executeXXXDemo() throws Exception{
Statement st = ConnFactory.getConn().createStatement();
String sql = "select * from book";
//String sql = "insert into book(name,price,pub) values('软件工程',22.35,'2015-12-05 22:12:23')";
//String sql = "update book set price=38.88 where name='软件工程'";
//String sql = "delete from book where name='软件工程'";
//st.executeQuery(sql);
//st.executeUpdate(sql);
boolean boo = st.execute(sql);
if(boo){
ResultSet rs = st.getResultSet();
while(rs.next()){
System.out.println(rs.getObject(2));
}
}
}</span>
案例、用户登录（通过用户输入信息来拼接sql语句----很危险）
<span style="font-size:18px;"><span style="white-space:pre"> </span>@Test//用户登录
public void login() throws Exception{
Connection con = ConnFactory.getConn();
Statement st = con.createStatement();
Scanner sc = new Scanner(System.in);
int id = sc.nextInt(); sc.nextLine();
String name = sc.nextLine();
String sql = "select count(*) from stud where id="+id+" and sname='"+name+"'";
System.out.println("sql:"+sql);
ResultSet rs = st.executeQuery(sql);
rs.next();
int a = rs.getInt(1);
if(a<=0){
System.out.println("登录不成功");
}else{
System.out.println("登录成功");
}
con.close();
}</span>黑的方法，输入：1002(回车) 1‘ or ‘1‘=‘1况，应该用PreparedStatement来解决！
<span style="font-size:18px;"><span style="white-space:pre"> </span>@Test//用户登录 黑：1002(回车) 1' or '1'='1
public void login2() throws Exception{
Scanner sc = new Scanner(System.in);
Connection con = ConnFactory.getConn();
String sql = "select count(*) from stud where id=? and sname=?";//需要用户输入的地方，用占位符('?')来代替，然后在后续通过设参来给占位符赋值
PreparedStatement pst = con.prepareStatement(sql);
//设置参数
int id = sc.nextInt(); sc.nextLine();
pst.setInt(1, id); //参数1----代表第1个占位符
String name = sc.nextLine();
pst.setString(2, name);//参数2
ResultSet rs = pst.executeQuery();
rs.next();
int a = rs.getInt(1);
if(a<=0){
System.out.println("登录不成功");
}else{
System.out.println("登录成功");
}
con.close();
}</span>
<span style="font-size:18px;"><span style="white-space:pre"> </span>@Test //演示获取自动增长列如id
public void saveAuto() throws Exception{
Connection con = ConnFactory.getConn();
String sql = "insert into book(name,price,pub) values('JavaEE',100.8,'2013-06-12 08:30:30')";
Statement st = con.createStatement();
//st.executeUpdate(sql);
st.executeUpdate(sql,Statement.RETURN_GENERATED_KEYS);
ResultSet rs = st.getGeneratedKeys();//里面封装了自动生成的所有值
if(rs.next()){
int id = rs.getInt(1);//获取第1个自动增长列
System.out.println("自动增长的id:"+id);
}
System.out.println("-----------------");
//预处理语句
sql = "insert into book(name,price) values(?,?)";
PreparedStatement pst = con.prepareStatement(sql,Statement.RETURN_GENERATED_KEYS);
pst.setString(1, "计算机基础");
pst.setDouble(2, 28);
pst.executeUpdate();
ResultSet rs2 = pst.getGeneratedKeys();//里面封装了自动生成的所有值
if(rs2.next()){
int id = rs2.getInt(1);//获取第1个自动增长列
System.out.println("自动增长的id:"+id);
}
}</span>public void batch() throws Exception{
Connection con = ConnFactory.getConn();
String sql = "insert into book(name,price,pub) values('JavaEE',100.8,'2015-06-12 08:30:30')";
Statement st = con.createStatement();
for(int i=0;i<10;i++){
st.addBatch(sql);
}
sql = "update book set price=price*1.1 where price>100";
st.addBatch(sql);
int[] a = st.executeBatch();
for(int r:a){
System.out.println(r);//r为每条sql语句所影响的记录数
}
}public void preparedBatch() throws Exception{
Connection con = ConnFactory.getConn();
String sql = "insert into book(name,price,pub) values(?,?,?)";
PreparedStatement pst = con.prepareStatement(sql);
for(int i=0;i<5;i++){
pst.setString(1, "Java"+i);
pst.setDouble(2, 55.85+i);
pst.setString(3, "2016-12-10 07:07:08");
pst.addBatch(); //pst的方式不能带参数sql
}
//pst.executeBatch();
int[] a = pst.executeBatch();
for(int r:a){
System.out.println(r);//r为每条sql语句所影响的记录数
}
}
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原文地址：http://blog.csdn.net/u011479875/article/details/50946262
