Mybatis连接池

xml 形式配置 DataSource

[](javascript:void(0)😉

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
  PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-config.dtd">

<configuration>
  <properties resource="/com/cn/cs/config.properties"/>
  <environments default="development">
    <environment>
      <transactionManager type="JDBC"/>
      <dataSource type="POOLED">
        <property name="driver" value="${oracle.driver}"/>
        <property name="url" value="${oracle.url}"/>
        <property name="username" value="${oracle.username}"/>
        <property name="password" value="${oracle.password}"/>
        <property name="poolMaximumActiveConnections" value="10"/> <!--最大活跃连接数 -->
        <property name="poolMaximumIdleConnections" value="5"/>  <!--最大空闲连接数-->
        <property name="poolTimeToWait" value="20000"/>　　<!--创建连接时最大等待时间20s-->
      </dataSource>
    </environment>
  </environments>
  <mappers>
      <mapper resource="/com/cn/cs/mapping/UserCsMapper.xml"/>  
  </mappers>
</configuration>
 

[](javascript:void(0)😉

mybatis 中 DataSource 节点有一个 type 属性. 有三个可选值: pooled(连接池), unpooled(非连接池), jndi

mybatis 内部定义了一个 DataSourceFactory 接口

[](javascript:void(0)😉

public interface DataSourceFactory {

  void setProperties(Properties props);

  DataSource getDataSource();

}

[](javascript:void(0)😉

根据 type 属性值分别对应实现类.

　 pooled --> PooledDataSourceFactory

​ unpooled --> UnpooledDataSourceFactory

　　jndi--> JndiDataSourceFactory

这三个实现类都实现了 DataSourceFactory 的 DataSource getDataSource() 方法.

PooledDataSourceFactory.getDataSource() 返回 PooledDataSource.

UnpooledDataSourceFactory.getDataSource() 返回 UnpooledDataSource

JndiDataSourceFactory.getDataSource() 返回 环境中的 DataSource

DataSource 将会保存在 Environment 的静态内部类 Builder 中.

连接池的初始化

dataSource 此时只会保存好配置信息. 连接池此时并没有创建好连接. 只有当程序在调用操作数据库的方法时, 才会出示化连接.

管理连接池的类为 PooledDateSource 这个类中有一个获取连接的方法.

这个方法会先判断是否有空闲连接, 有的话会直接将连接取出来. 如果没有则判断当前活跃的连接是否大于最大空闲连接数. 如果小于则创建一个新的连接.

否则将旧的连接删掉一个, 并创建一个新的连接.

[](javascript:void(0)😉

private PooledConnection popConnection(String username, String password) throws SQLException {
    boolean countedWait = false;
    PooledConnection conn = null;
    long t = System.currentTimeMillis();
    int localBadConnectionCount = 0;

    while (conn == null) {
      synchronized (state) {
        if (!state.idleConnections.isEmpty()) {
          // Pool has available connection
          conn = state.idleConnections.remove(0);
          if (log.isDebugEnabled()) {
            log.debug("Checked out connection " + conn.getRealHashCode() + " from pool.");
          }
        } else {
          // Pool does not have available connection
          if (state.activeConnections.size() < poolMaximumActiveConnections) {
            // Can create new connection
            conn = new PooledConnection(dataSource.getConnection(), this);
            if (log.isDebugEnabled()) {
              log.debug("Created connection " + conn.getRealHashCode() + ".");
            }
          } else {
            // Cannot create new connection
            PooledConnection oldestActiveConnection = state.activeConnections.get(0);
            long longestCheckoutTime = oldestActiveConnection.getCheckoutTime();
            if (longestCheckoutTime > poolMaximumCheckoutTime) {
              // Can claim overdue connection
              state.claimedOverdueConnectionCount++;
              state.accumulatedCheckoutTimeOfOverdueConnections += longestCheckoutTime;
              state.accumulatedCheckoutTime += longestCheckoutTime;
              state.activeConnections.remove(oldestActiveConnection);
              if (!oldestActiveConnection.getRealConnection().getAutoCommit()) {
                try {
                  oldestActiveConnection.getRealConnection().rollback();
                } catch (SQLException e) {
                  /*
                     Just log a message for debug and continue to execute the following
                     statement like nothing happened.
                     Wrap the bad connection with a new PooledConnection, this will help
                     to not interrupt current executing thread and give current thread a
                     chance to join the next competition for another valid/good database
                     connection. At the end of this loop, bad {@link @conn} will be set as null.
                   */
                  log.debug("Bad connection. Could not roll back");
                }
              }
              conn = new PooledConnection(oldestActiveConnection.getRealConnection(), this);
              conn.setCreatedTimestamp(oldestActiveConnection.getCreatedTimestamp());
              conn.setLastUsedTimestamp(oldestActiveConnection.getLastUsedTimestamp());
              oldestActiveConnection.invalidate();
              if (log.isDebugEnabled()) {
                log.debug("Claimed overdue connection " + conn.getRealHashCode() + ".");
              }
            } else {
              // Must wait
              try {
                if (!countedWait) {
                  state.hadToWaitCount++;
                  countedWait = true;
                }
                if (log.isDebugEnabled()) {
                  log.debug("Waiting as long as " + poolTimeToWait + " milliseconds for connection.");
                }
                long wt = System.currentTimeMillis();
                state.wait(poolTimeToWait);
                state.accumulatedWaitTime += System.currentTimeMillis() - wt;
              } catch (InterruptedException e) {
                break;
              }
            }
          }
        }
        if (conn != null) {
          // ping to server and check the connection is valid or not
          if (conn.isValid()) {
            if (!conn.getRealConnection().getAutoCommit()) {
              conn.getRealConnection().rollback();
            }
            conn.setConnectionTypeCode(assembleConnectionTypeCode(dataSource.getUrl(), username, password));
            conn.setCheckoutTimestamp(System.currentTimeMillis());
            conn.setLastUsedTimestamp(System.currentTimeMillis());
            state.activeConnections.add(conn);
            state.requestCount++;
            state.accumulatedRequestTime += System.currentTimeMillis() - t;
          } else {
            if (log.isDebugEnabled()) {
              log.debug("A bad connection (" + conn.getRealHashCode() + ") was returned from the pool, getting another connection.");
            }
            state.badConnectionCount++;
            localBadConnectionCount++;
            conn = null;
            if (localBadConnectionCount > (poolMaximumIdleConnections + poolMaximumLocalBadConnectionTolerance)) {
              if (log.isDebugEnabled()) {
                log.debug("PooledDataSource: Could not get a good connection to the database.");
              }
              throw new SQLException("PooledDataSource: Could not get a good connection to the database.");
            }
          }
        }
      }

    }

    if (conn == null) {
      if (log.isDebugEnabled()) {
        log.debug("PooledDataSource: Unknown severe error condition.  The connection pool returned a null connection.");
      }
      throw new SQLException("PooledDataSource: Unknown severe error condition.  The connection pool returned a null connection.");
    }

    return conn;
  }