mybatis 连接池配置

xml形式配置DataSource

<?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 id="development">
      <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>

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

public interface DataSourceFactory {

  void setProperties(Properties props);

  DataSource getDataSource();

}

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.

 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;
  }

mybatis 连接池配置

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