概念：是一个容器(在Java中就是一个集合)，存放数据库连接的容器。当系统初始化好之后，容器被创建，容器中会申请一些连接对象，当用户来访问数据库时，从容器中获取连接对象，用户访问完之后，会将连接对象归还给容器。
不像之前的代码一样，每次开始前都建立一个连接，然后结束时close，释放连接。
好处：节约资源、高效。
实现：
标准接口：DataSource javax.sql包下的。获取连接getConnection方法.调用Connection.close()方法，就实现了归还连接到连接池。
一般由数据库厂商来实现。
两种数据库连接池实现技术C3P0、Druid。
使用步骤：
1、导入jar包。有两个jar包，均需要导入。
2、需要定义配置文件 文件名为c3p0.properties或者c3p0-config.xml。目录为src。
3、创建核心对象 数据库连接池对象 ComboPooledDataSource。
4、获取连接getConnection
注意：不要忘记导入数据库的驱动jar包
com.mysql.jdbc.Driver root 123456 2 30 10 2 50 com.mysql.jdbc.Driver jdbc:mysql://127.0.0.1:3306/demo root 123456 5 100 50 1000 0 5
有多个配置，分别是默认配置和命名配置。
package com.itcast.dataSource;
import com.mchange.v2.c3p0.ComboPooledDataSource;
import org.junit.Test;
import javax.sql.DataSource;
import java.sql.Connection;
import java.sql.SQLException;
public class c3p0_demo1 {
public static void main(String[] args) {
ComboPooledDataSource dataSource = new ComboPooledDataSource();
try {
Connection connection = dataSource.getConnection();
System.out.println(connection);
} catch (SQLException e) {
e.printStackTrace();
}
}
}
"C:Program FilesJavajdk1.8.0_221binjava.exe" "-javaagent:C:Program FilesJetBrainsIntelliJ IDEA 2021.2libidea_rt.jar=53849:C:Program FilesJetBrainsIntelliJ IDEA 2021.2bin" -Dfile.encoding=UTF-8 -classpath "C:Program FilesJavajdk1.8.0_221jrelibcharsets.jar;C:Program FilesJavajdk1.8.0_221jrelibdeploy.jar;C:Program FilesJavajdk1.8.0_221jrelibextaccess-bridge-64.jar;C:Program FilesJavajdk1.8.0_221jrelibextcldrdata.jar;C:Program FilesJavajdk1.8.0_221jrelibextdnsns.jar;C:Program FilesJavajdk1.8.0_221jrelibextjaccess.jar;C:Program FilesJavajdk1.8.0_221jrelibextjfxrt.jar;C:Program FilesJavajdk1.8.0_221jrelibextlocaledata.jar;C:Program FilesJavajdk1.8.0_221jrelibextnashorn.jar;C:Program FilesJavajdk1.8.0_221jrelibextsunec.jar;C:Program FilesJavajdk1.8.0_221jrelibextsunjce_provider.jar;C:Program FilesJavajdk1.8.0_221jrelibextsunmscapi.jar;C:Program FilesJavajdk1.8.0_221jrelibextsunpkcs11.jar;C:Program FilesJavajdk1.8.0_221jrelibextzipfs.jar;C:Program FilesJavajdk1.8.0_221jrelibjavaws.jar;C:Program FilesJavajdk1.8.0_221jrelibjce.jar;C:Program FilesJavajdk1.8.0_221jrelibjfr.jar;C:Program FilesJavajdk1.8.0_221jrelibjfxswt.jar;C:Program FilesJavajdk1.8.0_221jrelibjsse.jar;C:Program FilesJavajdk1.8.0_221jrelibmanagement-agent.jar;C:Program FilesJavajdk1.8.0_221jrelibplugin.jar;C:Program FilesJavajdk1.8.0_221jrelibresources.jar;C:Program FilesJavajdk1.8.0_221jrelibrt.jar;E:java 学习代码my_jdbcoutproductionmy_jdbc;E:java 学习代码my_jdbclibsmysql-connector-java-5.1.48.jar;E:java 学习代码my_jdbclibsmchange-commons-java-0.2.3.4.jar;E:java 学习代码my_jdbclibsc3p0-0.9.2.1.jar;D:repositoryjunitjunit4.13.1junit-4.13.1.jar;D:repositoryorghamcresthamcrest-core1.3hamcrest-core-1.3.jar" com.itcast.dataSource.c3p0_demo1 二月 05, 2022 10:41:44 上午 com.mchange.v2.log.MLogdruid使用信息: MLog clients using java 1.4+ standard logging. 二月 05, 2022 10:41:45 上午 com.mchange.v2.c3p0.C3P0Registry banner 信息: Initializing c3p0-0.9.2.1 [built 20-March-2013 10:47:27 +0000; debug? true; trace: 10] 二月 05, 2022 10:41:45 上午 com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource getPoolManager 信息: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 3, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitonClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, dataSourceName -> 1hge1elam1jfc32k17mzvgj|7eda2dbb, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.jdbc.Driver, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1hge1elam1jfc32k17mzvgj|7eda2dbb, idleConnectionTestPeriod -> 0, initialPoolSize -> 2, jdbcUrl -> jdbc:mysql://127.0.0.1:3306/demo?useUnicode=true&characterEncoding=UTF-8, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 30, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 10, maxStatements -> 50, maxStatementsPerConnection -> 0, minPoolSize -> 2, numHelperThreads -> 3, preferredTestQuery -> null, properties -> {user=******, password=******}, propertyCycle -> 0, statementCacheNumDeferredCloseThreads -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, userOverrides -> {}, usesTraditionalReflectiveProxies -> false ] com.mchange.v2.c3p0.impl.NewProxyConnection@2f410acf Process finished with exit code 0
使用步骤：
1、导入jar包 除了有druid还有mysql的
2、定义配置文件 properties形式的 druid.properties。可以叫任意名称，可以放置在任意的目录下。手动加载。
driverClassName = com.mysql.jdbc.Driver url = jdbc:mysql://localhost:3306/demo username = root password = 123456 initialSize = 5 maxActive = 10 maxWait = 3000
3、获取数据库连接池对象 通过工厂类来获取 DruidDataSourceFactory
4、获取连接 getConnection
package com.itcast.dataSource;
import com.alibaba.druid.pool.DruidDataSourceFactory;
import javax.sql.DataSource;
import java.io.InputStream;
import java.sql.Connection;
import java.util.Properties;
public class druid_demo1 {
public static void main(String[] args)throws Exception {
//加载配置文件
Properties properties = new Properties();
InputStream inputStream = druid_demo1.class.getClassLoader().getResourceAsStream("druid.properties");
properties.load(inputStream);
DataSource dataSource = DruidDataSourceFactory.createDataSource(properties);
Connection connection = dataSource.getConnection();
System.out.println(connection);
}
}
二月 05, 2022 11:03:07 上午 com.alibaba.druid.pool.DruidDataSource info
信息: {dataSource-1} inited
com.mysql.jdbc.JDBC4Connection@7bfcd12c
Process finished with exit code 0
连接池工具类
一般情况下，还是使用工具类JDBCUtils
方法：获取连接的方法 释放资源 获取连接池的方法
提供静态代码块加载配置文件，初始化连接池对象
package com.itcast.dataSource;
import com.alibaba.druid.pool.DruidDataSourceFactory;
import javax.sql.DataSource;
import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
//连接池工具类
public class JDBCUtils {
private static DataSource ds;
static {
try {
Properties properties = new Properties();
InputStream inputStream = JDBCUtils.class.getClassLoader().getResourceAsStream("druid.properties");
properties.load(inputStream);
try {
ds = DruidDataSourceFactory.createDataSource(properties);
} catch (Exception e) {
e.printStackTrace();
}
} catch (IOException e) {
e.printStackTrace();
}
}
//获取连接方法
public static Connection getConnection() throws Exception{
return ds.getConnection();
}
//释放资源方法 方法的重载
public static void close(Statement stmt, Connection conn){
if (stmt != null){
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
//方法的重载
public static void close(Statement stmt, Connection conn, ResultSet res){
if (stmt != null){
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (res != null){
try {
res.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
//获取连接池的方法
public static DataSource getDatasource(){
return ds;
}
}
package com.itcast.dataSource;
import java.sql.Connection;
import java.sql.Statement;
public class druid_JDBCUtils {
public static void main(String[] args) {
Connection connection = null;
Statement statement = null;
try {
connection = JDBCUtils.getConnection();
statement = connection.createStatement();
String sql = "insert into actor values(null,'Amy','女','1999-9-15','550')";
int i = statement.executeUpdate(sql);
if (i>0){
System.out.println("执行成功");
}else {
System.out.println("执行失败");
}
} catch (Exception e) {
e.printStackTrace();
}finally {
JDBCUtils.close(statement,connection);
}
}
}
二月 05, 2022 4:54:29 下午 com.alibaba.druid.pool.DruidDataSource info
信息: {dataSource-1} inited
执行成功
Process finished with exit code 0
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