JDBC例子和c3p0連線池
阿新 • • 發佈：2018-12-28
package com.tedu; import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; /** * JDBC快速入門案例 * * @author Administrator * */ public class JDBCDemo1 { public static void main(String[] args) { Connection conn = null; Statement stat = null; ResultSet rs = null; try { // 1.註冊資料庫驅動(讓JDBC程式管理mysql的jar包) Class.forName("com.mysql.jdbc.Driver"); // 2.獲取資料庫連線() // Connection conn = // DriverManager.getConnection("jdbc:mysql://localhost:3306/jt_db","root",""); conn = DriverManager.getConnection("jdbc:mysql:///jt_db?useUnicode=true&characterEncoding=utf-8", "root", ""); // 3.獲取傳輸器 stat = conn.createStatement(); // 4.宣告SQL併發送SQL到資料庫執行，返回執行結果 String sql = "select * from account"; rs = stat.executeQuery(sql); // 5.處理結果 System.out.println(rs.next()); while (rs.next()) { int id = rs.getInt("id"); String name = rs.getString("name"); double money = rs.getDouble("money"); System.out.println(id + ":" + name + ":" + money); } } catch (Exception e) { e.printStackTrace(); System.out.println("查詢失敗"); } finally { // 6.釋放資源(越晚獲取的越先關閉) if (rs != null) { try { rs.close(); } catch (SQLException e) { e.printStackTrace(); } finally { rs = null; } } if (stat != null) { try { stat.close(); } catch (SQLException e) { e.printStackTrace(); } finally { stat = null; } } if (conn != null) { try { conn.close(); } catch (SQLException e) { e.printStackTrace(); } finally { conn = null; } } } } }
查詢用的是executeQuery(sql) 增刪改用的是executeUpdate(sql)
使用c3p0連線池，匯入c3p0的jar包，要注意c3p0-config.xml檔案的配置 ，如下：
<?xml version="1.0" encoding="UTF-8"?>
<c3p0-config>
<default-config>
<property name="driverClass">
com.mysql.jdbc.Driver
</property>
<property name="jdbcUrl">
jdbc:mysql:///jt_db?useUnicode=true&characterEncoding=utf-8
</property>
<property name="user">
root
</property>
<property name="password">
</property>
</default-config>
</c3p0-config>
package com.tedu; import java.sql.Connection; import java.sql.ResultSet; import java.sql.SQLException; import java.sql.Statement; import com.mchange.v2.c3p0.ComboPooledDataSource; /** * JDBC快速入門案例 * * @author Administrator * */ public class Testc3p0 { @SuppressWarnings({ "unused", "null" }) public static void main(String[] args) { Connection conn = null; Statement stat = null; ResultSet rs = null; //0.建立一個連線池物件 ComboPooledDataSource pool =new ComboPooledDataSource(); try { // //配置連線資料庫的基本資訊 // pool.setDriverClass("com.mysql.jdbc.Driver"); // pool.setJdbcUrl("jdbc:mysql:///jt_db?useUnicode=true&characterEncoding=utf8"); // pool.setUser("root"); // pool.setPassword(""); //1.從連線池中獲取一個連線物件 conn = pool.getConnection(); // 3.獲取傳輸器 stat = conn.createStatement(); // 4.宣告SQL併發送SQL到資料庫執行，返回執行結果 String sql = "select * from account"; rs = stat.executeQuery(sql); // 5.處理結果 while (rs.next()) { int id = rs.getInt("id"); String name = rs.getString("name"); double money = rs.getDouble("money"); System.out.println(id + ":" + name + ":" + money); } } catch (Exception e) { e.printStackTrace(); System.out.println("查詢失敗"); } finally { // 6.釋放資源(越晚獲取的越先關閉) if (rs != null) { try { rs.close(); } catch (SQLException e) { e.printStackTrace(); } finally { rs = null; } } if (stat != null) { try { stat.close(); } catch (SQLException e) { e.printStackTrace(); } finally { stat = null; } } if (conn != null) { try { //如果conn是自己建立的，就是原生的Connection，沒有被改造，呼叫close就是關閉連線， //如果conn是從連線池中獲取的連線物件，這個連線已經被改造過了，呼叫close方法就是將連線還給連線池 conn.close(); } catch (SQLException e) { e.printStackTrace(); } finally { conn = null; } } } } }
PreparedStatement 可以有效的防止SQL注入，例子：
public static Connection getConn() throws Exception{
//1.註冊驅動
Class.forName( "com.mysql.jdbc.Driver" );
//2.獲取連線
Connection conn = DriverManager.getConnection(
"jdbc:mysql:///jt_db?useUnicode=true&characterEncoding=utf-8",
"root",
"");
return conn;
}
public static void close(Connection conn,
Statement stat, ResultSet rs){
if(rs != null){
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
} finally{
rs = null;
}
}
if(stat != null){
try {
stat.close();
} catch (SQLException e) {
e.printStackTrace();
} finally{
stat = null;
}
}
if(conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
} finally{
conn = null;
}
}
}
private static void loginByPS(String username, String pwd) {
Connection conn =null;
PreparedStatement ps=null;
ResultSet rs=null;
try {
conn=JDBCUtil.getConn();
String sql="select * from user where username=? and password=?";
ps=conn.prepareStatement(sql);
ps.setString(1, username);
ps.setString(2, pwd);
rs=ps.executeQuery();
if(rs.next())
{
System.out.println("登入成功！！！");
}else{
System.out.println("使用者名稱或密碼不正確");
}
} catch (Exception e) {
e.printStackTrace();
System.out.println("登入失敗！！！");
}finally{
//釋放資源
JDBCUtil.close(conn, ps, rs);
}
}