数据库连接池的一些基本理解，c3p0和druid

数据库连接池

1，概念：

其实就是一个容器（集合），存放数据库连接的容器。

当系统初始化好后，容器被创建，容器中会申请一些连接对象，当用户来采访数据时，从容器中获取连接对象，用户访问完后，会将连接对象归还给容器

2，好处：

1，节约资源

2，用户访问高效

3，实现：

1，标准接口：DataSource java.xql包下的

这个接口是没有java官方是没有提供实现类的！

方法：

获取连接：Connection getConnection()
​
归还连接：如果连接对象Connection是从连接池里获得的，那么调用Connection.close()方法，则不会再关闭连接了，而是归还连接

2，一般我们不去实现它，有数据库厂商来实现

1，C3P0：数据库连接池技术

2，Druid：数据库连接池的技术，由阿里巴巴提供的

C3P0

• 步骤：

• 1，导入两个jar包，也不要忘了导入musql那个jar包

  c3p0-0.9.5.2.jar        mchange-commons-java-0.2.12.jar

• 2，定义配置文件

  配置文件名称：

  c3p0.properties 或 c3p0-config.xml

  xml文件内容： xml文件名就是上面那个

  <c3p0-config>
      <!--使用默认的配置读取连接池对象 -->
      <default-config>
          <!--连接参数-->
          <property name="driverClass">com.mysql.jdbc.Driver</property>
          <property name="jdbcUrl">jdbc:mysql:///zhoupeng</property>
          <property name="user">root</property>
          <property name="password">root</property>
  <!--        连接池参数-->
          <property name="initialPoolSize">5</property> <!--//初始化连接池-->
          <property name="maxPoolSize">10</property><!--连接池最大数-->
          <property name="checkoutTimeout">3000</property><!--初始化等待时间，如果3秒没有创建完成，会出异常-->
      </default-config>
      <named-config name="otherc3p0">
          <!--连接参数-->
          <property name="driverClass">com.mysql.jdbc.Driver</property>
          <property name="jdbcUrl">jdbc:mysql:///zhoupeng</property>
          <property name="user">root</property>
          <property name="password">root</property>
          <!--连接池参数-->
          <property name="initialPoolSize">5</property>
          <property name="maxPoolSize">8</property>
          <property name="checkoutTimeout">1000</property>
      </named-config>
  </c3p0-config>

  路径：

  直接将文件放在src目录下

• 3，创建核心对象 数据库连接池对象 ComboPooledDataSource

  DataSource dataSources = new ComboPooledDataSource();

• 4，获取连接：get Connection

   Connection connection = dataSources.getConnection();

c390xml文件的验证

<property name="maxPoolSize">10</property><!--连接池最大数-->

验证代码1：

        DataSource ds = new ComboPooledDataSource();
        for (int i = 0; i <10 ; i++) {
            Connection c = ds.getConnection();
            System.out.println(i+": "+c);
        }

验证代码2：

    DataSource ds = new ComboPooledDataSource();
        for (int i = 0; i <11 ; i++) {
            Connection c = ds.getConnection();
            System.out.println(i+": "+c);
        }

结果1：

0: com.mchange.v2.c3p0.impl.NewProxyConnection@3d5c822d [wrapping: com.mysql.jdbc.JDBC4Connection@6f46426d]
1: com.mchange.v2.c3p0.impl.NewProxyConnection@49c7b90e [wrapping: com.mysql.jdbc.JDBC4Connection@10d307f1]
2: com.mchange.v2.c3p0.impl.NewProxyConnection@3e84448c [wrapping: com.mysql.jdbc.JDBC4Connection@4a7f959b]
3: com.mchange.v2.c3p0.impl.NewProxyConnection@5403f35f [wrapping: com.mysql.jdbc.JDBC4Connection@483f6d77]
4: com.mchange.v2.c3p0.impl.NewProxyConnection@63a12c68 [wrapping: com.mysql.jdbc.JDBC4Connection@28f3b248]
5: com.mchange.v2.c3p0.impl.NewProxyConnection@32b260fa [wrapping: com.mysql.jdbc.JDBC4Connection@581ac8a8]
6: com.mchange.v2.c3p0.impl.NewProxyConnection@57d7f8ca [wrapping: com.mysql.jdbc.JDBC4Connection@76c3e77a]
7: com.mchange.v2.c3p0.impl.NewProxyConnection@67c33749 [wrapping: com.mysql.jdbc.JDBC4Connection@fba92d3]
8: com.mchange.v2.c3p0.impl.NewProxyConnection@fa49800 [wrapping: com.mysql.jdbc.JDBC4Connection@71238fc2]
9: com.mchange.v2.c3p0.impl.NewProxyConnection@16a0ee18 [wrapping: com.mysql.jdbc.JDBC4Connection@3d6f0054]

结果2：

0: com.mchange.v2.c3p0.impl.NewProxyConnection@3d5c822d [wrapping: com.mysql.jdbc.JDBC4Connection@6f46426d]
1: com.mchange.v2.c3p0.impl.NewProxyConnection@49c7b90e [wrapping: com.mysql.jdbc.JDBC4Connection@10d307f1]
2: com.mchange.v2.c3p0.impl.NewProxyConnection@3e84448c [wrapping: com.mysql.jdbc.JDBC4Connection@4a7f959b]
3: com.mchange.v2.c3p0.impl.NewProxyConnection@5403f35f [wrapping: com.mysql.jdbc.JDBC4Connection@483f6d77]
4: com.mchange.v2.c3p0.impl.NewProxyConnection@63a12c68 [wrapping: com.mysql.jdbc.JDBC4Connection@28f3b248]
5: com.mchange.v2.c3p0.impl.NewProxyConnection@32b260fa [wrapping: com.mysql.jdbc.JDBC4Connection@581ac8a8]
6: com.mchange.v2.c3p0.impl.NewProxyConnection@57d7f8ca [wrapping: com.mysql.jdbc.JDBC4Connection@76c3e77a]
7: com.mchange.v2.c3p0.impl.NewProxyConnection@67c33749 [wrapping: com.mysql.jdbc.JDBC4Connection@fba92d3]
8: com.mchange.v2.c3p0.impl.NewProxyConnection@fa49800 [wrapping: com.mysql.jdbc.JDBC4Connection@71238fc2]
9: com.mchange.v2.c3p0.impl.NewProxyConnection@16a0ee18 [wrapping: com.mysql.jdbc.JDBC4Connection@3d6f0054]

Exception in thread "main" java.sql.SQLException: An attempt by a client to checkout a Connection has timed out.
	at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:118)
	at com.mchange.v2.sql.SqlUtils.toSQLException(SqlUtils.java:77)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:690)
	at com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource.getConnection(AbstractPoolBackedDataSource.java:140)
	at ShuJuKuLianJieChi.main(ShuJuKuLianJieChi.java:12)
Caused by: com.mchange.v2.resourcepool.TimeoutException: A client timed out while waiting to acquire a resource from com.mchange.v2.resourcepool.BasicResourcePool@15aab8c6 -- timeout at awaitAvailable()
	at com.mchange.v2.resourcepool.BasicResourcePool.awaitAvailable(BasicResourcePool.java:1505)
	at com.mchange.v2.resourcepool.BasicResourcePool.prelimCheckoutResource(BasicResourcePool.java:644)
	at com.mchange.v2.resourcepool.BasicResourcePool.checkoutResource(BasicResourcePool.java:554)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutAndMarkConnectionInUse(C3P0PooledConnectionPool.java:758)
	at com.mchange.v2.c3p0.impl.C3P0PooledConnectionPool.checkoutPooledConnection(C3P0PooledConnectionPool.java:685)
	... 2 more

Druid

• 步骤：

• 1，还是先导jar包，druid-1.2.9.jar

• 2，定义配置文件

  可以是properties形式的

  可以任意名字，可以放任意目录（意思是需要手动导入了）

  建议还是放到src下

  dirverClassName=com.mysql.jdbc.Driver
  url=jdbc:mysql:///zhoupeng
  username=root
  password=root
  # 这些和刚刚c3p0的配置文件差不多，就不写多的注释了
  initialSize=5
  maxActive=10
  maxWait=3000

• 3，加载配置文件

  	Properties p = new Properties();
          InputStream in = DruidDemo.class.getClassLoader().getResourceAsStream("druid.properties");
          p.load(in);

• 4，获取数据库连接池对象：

  通过一个工厂来获取：DruidDataSourceFactory

   	
  
          DataSource ds = DruidDataSourceFactory.createDataSource(p);

• 5，获取连接，getConnection

Connection c=ds.getConnection();