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DBCP(DataBase connection pool),数据库连接池。是java数据库连接池的一种，由Apache开发， tomcat 使用的连接池组件，通过数据库连接池，可以让程序自动管理数据库连接的释放和断开。

单独使用dbcp需要3个包：common-dbcp.jar,common-pool.jar

由于建立数据库连接是一个非常耗时耗资源的行为，所以通过连接池预先同数据库建立一些连接，放在内存中，应用程序需要建立数据库连接时直接到连接池中申请一个就行，用完后再放回去。

【DBCP连接池的使用】

第一步：引入DBCP连接池的jar包.

第二步：编写DBCP代码：

    * 手动设置参数:

    * 配置文件设置参数:

DBCP连接池的两种使用方式：

(手动方式和配置文件方式)

/*** */
package com.dbcp;import java.io.FileInputStream;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;import javax.imageio.stream.FileImageInputStream;
import javax.sql.DataSource;import org.apache.commons.dbcp.BasicDataSource;
import org.apache.commons.dbcp.BasicDataSourceFactory;
import org.junit.Test;import com.jdbcutils.JDBCUtils;
import com.jdbcutils.JDBCUtils_ByFile;/*** DBCP连接池的使用* * @author 李 下午9:31:52*/
public class DBCPDemo {/*** 手动方式*/@Testpublic void demo1() {Connection conn = null;PreparedStatement stmt = null;ResultSet rs = null;BasicDataSource dataSource = new BasicDataSource();dataSource.setDriverClassName("com.mysql.jdbc.Driver");dataSource.setUrl("jdbc:mysql:///stu");dataSource.setUsername("root");dataSource.setPassword("420420");try {conn = dataSource.getConnection();String sql = "select * from student";stmt = conn.prepareStatement(sql);rs = stmt.executeQuery();while (rs.next()) {System.out.println(rs.getInt("id") + "  "+ rs.getString("name"));}} catch (SQLException e) {e.printStackTrace();} finally {JDBCUtils_ByFile.closeConnection(rs, stmt, conn);}}/*** 配置文件方式*/@Testpublic void demo2() {Connection conn = null;PreparedStatement stmt = null;ResultSet rs = null;try {//设置相关参数Properties properties = new Properties();properties.load(new FileInputStream("src/dbcpconfig.properties"));DataSource dataSource = BasicDataSourceFactory.createDataSource(properties);conn = dataSource.getConnection();String sql = "select * from student";stmt = conn.prepareStatement(sql);rs = stmt.executeQuery();while (rs.next()) {System.out.println(rs.getInt("id") + "  "+ rs.getString("name"));}} catch (Exception e) {e.printStackTrace();} finally {//该处为自定义的工具类，用来释放资源JDBCUtils_ByFile.closeConnection(rs, stmt, conn);}}
}

driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql:///stu
username=root
password=420420

/*** */
package com.jdbcutils;import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;/*** @author 李 下午7:29:53*/
public class JDBCUtils_ByFile {private static final String driverClass;private static final String url;private static final String username;private static final String password;/*** 读取配置文件*/static {Properties properties = null;try {InputStream in = new FileInputStream("src/jdbc.properties");properties = new Properties();properties.load(in);} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}driverClass = properties.getProperty("driverClass");url = properties.getProperty("url");username = properties.getProperty("username");password = properties.getProperty("password");}/*** 加载驱动*/public static void loadDriver() {try {Class.forName(driverClass);} catch (ClassNotFoundException e) {e.printStackTrace();}}/*** 连接数据库 并返回连接conn* * @return*/public static Connection getConnection() {Connection conn = null;try {loadDriver();conn = DriverManager.getConnection(url, username, password);} catch (SQLException e) {e.printStackTrace();}return conn;}/*** 释放资源* * @param rs*            结果集* @param stmt*            执行sql语句* @param conn*            连接*/public static void closeConnection(ResultSet rs, PreparedStatement stmt,Connection conn) {try {if (rs != null) {rs.close();}if (stmt != null) {stmt.close();}if (conn != null) {conn.close();}} catch (SQLException e) {e.printStackTrace();}}/*** 释放资源* * @param stmt*            执行sql语句* @param conn*            数据库连接*/public static void closeConnection(PreparedStatement stmt, Connection conn) {try {if (stmt != null) {stmt.close();}if (conn != null) {conn.close();}} catch (SQLException e) {e.printStackTrace();}}
}