原文链接 https://juejin.cn/post/6844903665094901767

UnpooledDataSourceFactory 非池化类

package org.apache.ibatis.datasource.unpooled;

package org.apache.ibatis.datasource.unpooled;
/**
 * @author Clinton Begin
 */
public class UnpooledDataSourceFactory implements DataSourceFactory {
  private static final String DRIVER_PROPERTY_PREFIX = "driver.";
  private static final int DRIVER_PROPERTY_PREFIX_LENGTH = DRIVER_PROPERTY_PREFIX.length();
  protected DataSource dataSource;
  public UnpooledDataSourceFactory() {
    this.dataSource = new UnpooledDataSource();
  }
  @Override
  public void setProperties(Properties properties) {
    Properties driverProperties = new Properties();
    MetaObject metaDataSource = SystemMetaObject.forObject(dataSource);
    for (Object key : properties.keySet()) {
      String propertyName = (String) key;
      if (propertyName.startsWith(DRIVER_PROPERTY_PREFIX)) {
        String value = properties.getProperty(propertyName);
        driverProperties.setProperty(propertyName.substring(DRIVER_PROPERTY_PREFIX_LENGTH), value);
      } else if (metaDataSource.hasSetter(propertyName)) {
        String value = (String) properties.get(propertyName);
        Object convertedValue = convertValue(metaDataSource, propertyName, value);
        metaDataSource.setValue(propertyName, convertedValue);
      } else {
        throw new DataSourceException("Unknown DataSource property: " + propertyName);
      }
    }
    if (driverProperties.size() > 0) {
      metaDataSource.setValue("driverProperties", driverProperties);
    }
  }
  @Override
  public DataSource getDataSource() {
    return dataSource;
  }
  private Object convertValue(MetaObject metaDataSource, String propertyName, String value) {
    Object convertedValue = value;
    Class<?> targetType = metaDataSource.getSetterType(propertyName);
    if (targetType == Integer.class || targetType == int.class) {
      convertedValue = Integer.valueOf(value);
    } else if (targetType == Long.class || targetType == long.class) {
      convertedValue = Long.valueOf(value);
    } else if (targetType == Boolean.class || targetType == boolean.class) {
      convertedValue = Boolean.valueOf(value);
    }
    return convertedValue;
  }
}

PooledDataSourceFactory\PooledDataSource 线程池

package org.apache.ibatis.datasource.pooled;

参数说明

1. poolMaximumActiveConnections ： 最大活跃数，默认值：10
2. poolMaximumIdleConnections ：最大空闲连接数，默认值：5
3. poolMaximumCheckoutTime :获取连接超时等待最大（checked out）时间，默认值：20000 毫秒
4. poolTimeToWait ： 单次获取连接 最大等待时间 默认：20000 毫秒
5. poolMaximumLocalBadConnectionTolerance 获取连接重试次数 默认：3
6. poolPingQuery 用于检测连接是否断开的测试语句，默认值：”NO PING QUERY SET”，一般设置为”select 1”
7. poolPingEnabled 是否通过执行poolPingQuery 语句做检测，默认值：false，必须为true才生效
8. poolPingConnectionsNotUsedFor 连接检测间隔时间 ，默认0。必须大0才生效

这3个参数是一起使用poolPingQuery、poolPingEnabled、poolPingConnectionsNotUsedFor

package org.apache.ibatis.datasource.pooled;
/**
 * @author Clinton Begin
 */
public class PooledDataSourceFactory extends UnpooledDataSourceFactory {
  public PooledDataSourceFactory() {
    this.dataSource = new PooledDataSource();
  }
}
/**
 * This is a simple, synchronous, thread-safe database connection pool.
 *
 * @author Clinton Begin
 */
public class PooledDataSource implements DataSource {
  private static final Log log = LogFactory.getLog(PooledDataSource.class);
  private final PoolState state = new PoolState(this);
  private final UnpooledDataSource dataSource;
  // OPTIONAL CONFIGURATION FIELDS
  protected int poolMaximumActiveConnections = 10;
  protected int poolMaximumIdleConnections = 5;
  protected int poolMaximumCheckoutTime = 20000;
  protected int poolTimeToWait = 20000;
  protected int poolMaximumLocalBadConnectionTolerance = 3;
  protected String poolPingQuery = "NO PING QUERY SET";
  protected boolean poolPingEnabled;
  protected int poolPingConnectionsNotUsedFor;
  private int expectedConnectionTypeCode;
  public PooledDataSource() {
    dataSource = new UnpooledDataSource();
  }
  public PooledDataSource(UnpooledDataSource dataSource) {
    this.dataSource = dataSource;
  }
  public PooledDataSource(String driver, String url, String username, String password) {
    dataSource = new UnpooledDataSource(driver, url, username, password);
    expectedConnectionTypeCode = assembleConnectionTypeCode(dataSource.getUrl(), dataSource.getUsername(), dataSource.getPassword());
  }
  public PooledDataSource(String driver, String url, Properties driverProperties) {
    dataSource = new UnpooledDataSource(driver, url, driverProperties);
    expectedConnectionTypeCode = assembleConnectionTypeCode(dataSource.getUrl(), dataSource.getUsername(), dataSource.getPassword());
  }
  public PooledDataSource(ClassLoader driverClassLoader, String driver, String url, String username, String password) {
    dataSource = new UnpooledDataSource(driverClassLoader, driver, url, username, password);
    expectedConnectionTypeCode = assembleConnectionTypeCode(dataSource.getUrl(), dataSource.getUsername(), dataSource.getPassword());
  }
  public PooledDataSource(ClassLoader driverClassLoader, String driver, String url, Properties driverProperties) {
    dataSource = new UnpooledDataSource(driverClassLoader, driver, url, driverProperties);
    expectedConnectionTypeCode = assembleConnectionTypeCode(dataSource.getUrl(), dataSource.getUsername(), dataSource.getPassword());
  }
  ...
  ...
  ...
}

数据库连接池维护操作

核心两个方法：

pushConnection

这个方法简单一看就明白了。

protected void pushConnection(PooledConnection conn) throws SQLException {
  synchronized (state) {
    state.activeConnections.remove(conn);
    if (conn.isValid()) {
      if (state.idleConnections.size() < poolMaximumIdleConnections && conn.getConnectionTypeCode() == expectedConnectionTypeCode) {
        state.accumulatedCheckoutTime += conn.getCheckoutTime();
        if (!conn.getRealConnection().getAutoCommit()) {
          conn.getRealConnection().rollback();
        }
        PooledConnection newConn = new PooledConnection(conn.getRealConnection(), this);
        state.idleConnections.add(newConn);
        newConn.setCreatedTimestamp(conn.getCreatedTimestamp());
        newConn.setLastUsedTimestamp(conn.getLastUsedTimestamp());
        conn.invalidate();
        if (log.isDebugEnabled()) {
          log.debug("Returned connection " + newConn.getRealHashCode() + " to pool.");
        }
        // 线程唤醒
        state.notifyAll();
      } else {
        state.accumulatedCheckoutTime += conn.getCheckoutTime();
        if (!conn.getRealConnection().getAutoCommit()) {
          conn.getRealConnection().rollback();
        }
        conn.getRealConnection().close();
        if (log.isDebugEnabled()) {
          log.debug("Closed connection " + conn.getRealHashCode() + ".");
        }
        conn.invalidate();
      }
    } else {
      if (log.isDebugEnabled()) {
        log.debug("A bad connection (" + conn.getRealHashCode() + ") attempted to return to the pool, discarding connection.");
      }
      state.badConnectionCount++;
    }
  }
}

popConnection

这个方法稍微复杂一点，这里涉及到synchronized锁机制（死循环取连接）、连接超时、超过本地错误最大连接报错

private PooledConnection popConnection(String username, String password) throws SQLException {
  boolean countedWait = false;
  PooledConnection conn = null;
  long t = System.currentTimeMillis();
  int localBadConnectionCount = 0;
  // 重点看一下
  while (conn == null) {
    // 重点看一下
    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 {
        // 未超过最大连接数，直接创建新的连接
        // 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 {
          // 连接池取一个连接，check是否超过最大连接时间，未超过就取出来使用，超过继续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 {
            // 到这里说明mysql连接池已经打满已经达到最大数，必须等待等待其他线程唤醒，state.notifyAll(); 
            // 如果超过最大时间还未唤醒就累计错误连接，如果超过最大错误连接数服务会报错
            // 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) {
              // set interrupt flag
              Thread.currentThread().interrupt();
              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;
          // 重点分析
          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;
}

PoolState 线程池状态类

package org.apache.ibatis.datasource.pooled;
import java.util.ArrayList;
import java.util.List;
/**
 * @author Clinton Begin
 */
public class PoolState {
  protected PooledDataSource dataSource;
  protected final List<PooledConnection> idleConnections = new ArrayList<>();
  protected final List<PooledConnection> activeConnections = new ArrayList<>();
  protected long requestCount = 0;
  protected long accumulatedRequestTime = 0;
  protected long accumulatedCheckoutTime = 0;
  protected long claimedOverdueConnectionCount = 0;
  protected long accumulatedCheckoutTimeOfOverdueConnections = 0;
  protected long accumulatedWaitTime = 0;
  protected long hadToWaitCount = 0;
  protected long badConnectionCount = 0;
  public PoolState(PooledDataSource dataSource) {
    this.dataSource = dataSource;
  }
  public synchronized long getRequestCount() {
    return requestCount;
  }
  public synchronized long getAverageRequestTime() {
    return requestCount == 0 ? 0 : accumulatedRequestTime / requestCount;
  }
  public synchronized long getAverageWaitTime() {
    return hadToWaitCount == 0 ? 0 : accumulatedWaitTime / hadToWaitCount;
  }
  public synchronized long getHadToWaitCount() {
    return hadToWaitCount;
  }
  public synchronized long getBadConnectionCount() {
    return badConnectionCount;
  }
  public synchronized long getClaimedOverdueConnectionCount() {
    return claimedOverdueConnectionCount;
  }
  public synchronized long getAverageOverdueCheckoutTime() {
    return claimedOverdueConnectionCount == 0 ? 0 : accumulatedCheckoutTimeOfOverdueConnections / claimedOverdueConnectionCount;
  }
  public synchronized long getAverageCheckoutTime() {
    return requestCount == 0 ? 0 : accumulatedCheckoutTime / requestCount;
  }
  public synchronized int getIdleConnectionCount() {
    return idleConnections.size();
  }
  public synchronized int getActiveConnectionCount() {
    return activeConnections.size();
  }
  @Override
  public synchronized String toString() {
    StringBuilder builder = new StringBuilder();
    builder.append("\n===CONFIGURATION==============================================");
    builder.append("\n jdbcDriver                     ").append(dataSource.getDriver());
    builder.append("\n jdbcUrl                        ").append(dataSource.getUrl());
    builder.append("\n jdbcUsername                   ").append(dataSource.getUsername());
    builder.append("\n jdbcPassword                   ").append(dataSource.getPassword() == null ? "NULL" : "************");
    builder.append("\n poolMaxActiveConnections       ").append(dataSource.poolMaximumActiveConnections);
    builder.append("\n poolMaxIdleConnections         ").append(dataSource.poolMaximumIdleConnections);
    builder.append("\n poolMaxCheckoutTime            ").append(dataSource.poolMaximumCheckoutTime);
    builder.append("\n poolTimeToWait                 ").append(dataSource.poolTimeToWait);
    builder.append("\n poolPingEnabled                ").append(dataSource.poolPingEnabled);
    builder.append("\n poolPingQuery                  ").append(dataSource.poolPingQuery);
    builder.append("\n poolPingConnectionsNotUsedFor  ").append(dataSource.poolPingConnectionsNotUsedFor);
    builder.append("\n ---STATUS-----------------------------------------------------");
    builder.append("\n activeConnections              ").append(getActiveConnectionCount());
    builder.append("\n idleConnections                ").append(getIdleConnectionCount());
    builder.append("\n requestCount                   ").append(getRequestCount());
    builder.append("\n averageRequestTime             ").append(getAverageRequestTime());
    builder.append("\n averageCheckoutTime            ").append(getAverageCheckoutTime());
    builder.append("\n claimedOverdue                 ").append(getClaimedOverdueConnectionCount());
    builder.append("\n averageOverdueCheckoutTime     ").append(getAverageOverdueCheckoutTime());
    builder.append("\n hadToWait                      ").append(getHadToWaitCount());
    builder.append("\n averageWaitTime                ").append(getAverageWaitTime());
    builder.append("\n badConnectionCount             ").append(getBadConnectionCount());
    builder.append("\n===============================================================");
    return builder.toString();
  }
}

Configuration类

package org.apache.ibatis.session;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import java.util.Set;
import java.util.function.BiFunction;
/**
 * @author Clinton Begin
 */
public class Configuration {
  protected Environment environment;
  protected boolean safeRowBoundsEnabled;
  protected boolean safeResultHandlerEnabled = true;
  protected boolean mapUnderscoreToCamelCase;
  protected boolean aggressiveLazyLoading;
  protected boolean multipleResultSetsEnabled = true;
  protected boolean useGeneratedKeys;
  protected boolean useColumnLabel = true;
  protected boolean cacheEnabled = true;
  protected boolean callSettersOnNulls;
  protected boolean useActualParamName = true;
  protected boolean returnInstanceForEmptyRow;
  protected boolean shrinkWhitespacesInSql;
  protected boolean nullableOnForEach;
  protected boolean argNameBasedConstructorAutoMapping;
  protected String logPrefix;
  protected Class<? extends Log> logImpl;
  protected Class<? extends VFS> vfsImpl;
  protected Class<?> defaultSqlProviderType;
  protected LocalCacheScope localCacheScope = LocalCacheScope.SESSION;
  protected JdbcType jdbcTypeForNull = JdbcType.OTHER;
  protected Set<String> lazyLoadTriggerMethods = new HashSet<>(Arrays.asList("equals", "clone", "hashCode", "toString"));
  protected Integer defaultStatementTimeout;
  protected Integer defaultFetchSize;
  protected ResultSetType defaultResultSetType;
  protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE;
  protected AutoMappingBehavior autoMappingBehavior = AutoMappingBehavior.PARTIAL;
  protected AutoMappingUnknownColumnBehavior autoMappingUnknownColumnBehavior = AutoMappingUnknownColumnBehavior.NONE;
  protected Properties variables = new Properties();
  protected ReflectorFactory reflectorFactory = new DefaultReflectorFactory();
  protected ObjectFactory objectFactory = new DefaultObjectFactory();
  protected ObjectWrapperFactory objectWrapperFactory = new DefaultObjectWrapperFactory();
  protected boolean lazyLoadingEnabled = false;
  protected ProxyFactory proxyFactory = new JavassistProxyFactory(); // #224 Using internal Javassist instead of OGNL
  protected String databaseId;
  /**
   * Configuration factory class.
   * Used to create Configuration for loading deserialized unread properties.
   *
   * @see <a href='https://github.com/mybatis/old-google-code-issues/issues/300'>Issue 300 (google code)</a>
   */
  protected Class<?> configurationFactory;
  protected final MapperRegistry mapperRegistry = new MapperRegistry(this);
  protected final InterceptorChain interceptorChain = new InterceptorChain();
  protected final TypeHandlerRegistry typeHandlerRegistry = new TypeHandlerRegistry(this);
  protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();
  protected final LanguageDriverRegistry languageRegistry = new LanguageDriverRegistry();
  protected final Map<String, MappedStatement> mappedStatements = new StrictMap<MappedStatement>("Mapped Statements collection")
      .conflictMessageProducer((savedValue, targetValue) ->
          ". please check " + savedValue.getResource() + " and " + targetValue.getResource());
  protected final Map<String, Cache> caches = new StrictMap<>("Caches collection");
  protected final Map<String, ResultMap> resultMaps = new StrictMap<>("Result Maps collection");
  protected final Map<String, ParameterMap> parameterMaps = new StrictMap<>("Parameter Maps collection");
  protected final Map<String, KeyGenerator> keyGenerators = new StrictMap<>("Key Generators collection");
  protected final Set<String> loadedResources = new HashSet<>();
  protected final Map<String, XNode> sqlFragments = new StrictMap<>("XML fragments parsed from previous mappers");
  protected final Collection<XMLStatementBuilder> incompleteStatements = new LinkedList<>();
  protected final Collection<CacheRefResolver> incompleteCacheRefs = new LinkedList<>();
  protected final Collection<ResultMapResolver> incompleteResultMaps = new LinkedList<>();
  protected final Collection<MethodResolver> incompleteMethods = new LinkedList<>();
  /*
   * A map holds cache-ref relationship. The key is the namespace that
   * references a cache bound to another namespace and the value is the
   * namespace which the actual cache is bound to.
   */
  protected final Map<String, String> cacheRefMap = new HashMap<>();
  public Configuration(Environment environment) {
    this();
    this.environment = environment;
  }
  public Configuration() {
    typeAliasRegistry.registerAlias("JDBC", JdbcTransactionFactory.class);
    typeAliasRegistry.registerAlias("MANAGED", ManagedTransactionFactory.class);
    typeAliasRegistry.registerAlias("JNDI", JndiDataSourceFactory.class);
    typeAliasRegistry.registerAlias("POOLED", PooledDataSourceFactory.class);
    typeAliasRegistry.registerAlias("UNPOOLED", UnpooledDataSourceFactory.class);
    typeAliasRegistry.registerAlias("PERPETUAL", PerpetualCache.class);
    typeAliasRegistry.registerAlias("FIFO", FifoCache.class);
    typeAliasRegistry.registerAlias("LRU", LruCache.class);
    typeAliasRegistry.registerAlias("SOFT", SoftCache.class);
    typeAliasRegistry.registerAlias("WEAK", WeakCache.class);
    typeAliasRegistry.registerAlias("DB_VENDOR", VendorDatabaseIdProvider.class);
    typeAliasRegistry.registerAlias("XML", XMLLanguageDriver.class);
    typeAliasRegistry.registerAlias("RAW", RawLanguageDriver.class);
    typeAliasRegistry.registerAlias("SLF4J", Slf4jImpl.class);
    typeAliasRegistry.registerAlias("COMMONS_LOGGING", JakartaCommonsLoggingImpl.class);
    typeAliasRegistry.registerAlias("LOG4J", Log4jImpl.class);
    typeAliasRegistry.registerAlias("LOG4J2", Log4j2Impl.class);
    typeAliasRegistry.registerAlias("JDK_LOGGING", Jdk14LoggingImpl.class);
    typeAliasRegistry.registerAlias("STDOUT_LOGGING", StdOutImpl.class);
    typeAliasRegistry.registerAlias("NO_LOGGING", NoLoggingImpl.class);
    typeAliasRegistry.registerAlias("CGLIB", CglibProxyFactory.class);
    typeAliasRegistry.registerAlias("JAVASSIST", JavassistProxyFactory.class);
    languageRegistry.setDefaultDriverClass(XMLLanguageDriver.class);
    languageRegistry.register(RawLanguageDriver.class);
  }