Mybatis源码-datasource(数据源)总结
这个包主要功能的如何获取到数据源对象， 间接获取Connection(连接对象)来操作数据库
1、获取DataSource方式有两种
1.1. 通过jndi的（InitialContext上下文）获取，jndi的lookup方法，从某个地方获取配置生成一个DataSource
1.2. 通过java代码，传入datasource需要参数，比如用户名、密码、驱动类路径等等
2、这个包一个关系的简图
3、PooledConnection类解析(部分核心代码）
package org.apache.ibatis.datasource.pooled;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.sql.Connection;
import java.sql.SQLException;
import org.apache.ibatis.reflection.ExceptionUtil;
/**
* 连接池
* 1、连接池数据源、真实连接和代理连接对象
* 2、还有时间相关，比如上一次使用连接对象的时间
* 3、实现InvocationHandler的invoke方法，这个方法就是在调用真实方法之前调用该方法，在创建代理对象时候将代理对象与InvocationHandler
* 进行关联，相当于类成员变量proxyConnection，代理对象关联本类的invoke方法，主要是为判断是否执行是close方法，执行
* close方法需要进行额外的操作
* @author Clinton Begin
*/
class PooledConnection implements InvocationHandler {
/**
* 关闭
*/
private static final String CLOSE = "close";
/**
* 连接类，创建代理对象用改的
*/
private static final Class<?>[] IFACES = new Class<?>[] { Connection.class };
/**
* hashCode
*/
private final int hashCode;
/**
* 连接池数据源
*/
private final PooledDataSource dataSource;
/**
* 真实连接
*/
private final Connection realConnection;
/**
* 代理连接
*/
private final Connection proxyConnection;
/**
* 检出时间戳
*/
private long checkoutTimestamp;
/**
* 创建的时间戳
*/
private long createdTimestamp;
/**
* 最后使用的时间戳
*/
private long lastUsedTimestamp;
/**
* 这个主要用于区分唯一性， 用户名+密码+url生成hashCode 确定唯一性
*/
private int connectionTypeCode;
/**
* 是否有效 valid?
*/
private boolean valid;
/**
* 使用连接对象和连接池数据源对象
* Constructor for SimplePooledConnection that uses the Connection and PooledDataSource passed in.
*
* @param connection - the connection that is to be presented as a pooled connection
* @param dataSource - the dataSource that the connection is from
*/
public PooledConnection(Connection connection, PooledDataSource dataSource) {
//连接hashCode
//连接对象
//数据源
//创建时间戳
//最后使用时间戳
//初始化有效
//代理连接对象创建在执行proxyConnection的方法将会调用 当前invoke的方法
this.hashCode = connection.hashCode();
this.realConnection = connection;
this.dataSource = dataSource;
this.createdTimestamp = System.currentTimeMillis();
this.lastUsedTimestamp = System.currentTimeMillis();
this.valid = true;
this.proxyConnection = (Connection) Proxy.newProxyInstance(Connection.class.getClassLoader(), IFACES, this);
}
/**
* Required for InvocationHandler implementation.
* 实现InvocationHandler的实现方法， 代理对象是为了，判断方法是不是close方法
* @param proxy - not used
* @param method - the method to be executed
* @param args - the parameters to be passed to the method
* @see java.lang.reflect.InvocationHandler#invoke(Object, java.lang.reflect.Method, Object[])
*/
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
//获取Connection调用的方法的名称是不是close方法
//是需要关闭连接操作
String methodName = method.getName();
if (CLOSE.hashCode() == methodName.hashCode() && CLOSE.equals(methodName)) {
dataSource.pushConnection(this);
return null;
}
try {
if (!Object.class.equals(method.getDeclaringClass())) {
// issue #579 toString() should never fail
// throw an SQLException instead of a Runtime
checkConnection();
}
return method.invoke(realConnection, args);
} catch (Throwable t) {
throw ExceptionUtil.unwrapThrowable(t);
}
}
}
3.1 总结
- 这里关键地方应该是它创建一个代理Connection对象，主要拦截close方法，将用完连接对象放回池中
4、PooledDataSource
/**
* 这个是一个简单、同步，线程安全数据连接池
* This is a simple, synchronous, thread-safe database connection pool.
* 1、PooledDataSource和UnpooledDataSource的区别主要前面比后面多一个方法， 从线程中取连接对象，popConnection, 连接集合对象的状态
* 2、修改配置信息需要强制清空激活连接数集合和空闲连接对象集合
* 3、调用connection close的方法时候，它将用完的连接对象放回连接池，但是这个connection对象是不变，但是外面包PooledConnection变成最新的
* 4、完成线程池的功能主要利用PoolState类的中两个集合，活动连接集合和空闲连接集合， 包括里面一些统计操作
* @author Clinton Begin
*/
public class PooledDataSource implements DataSource {
/**
* 获取日志对象
*/
private static final Log log = LogFactory.getLog(PooledDataSource.class);
/**
* 根据当前对象创建连接池状态
*/
private final PoolState state = new PoolState(this);
/**
* 非连接池数据源
*/
private final UnpooledDataSource dataSource;
// OPTIONAL CONFIGURATION FIELDS
/**
* 连接池活动连接对象默认是10
*/
protected int poolMaximumActiveConnections = 10;
/**
* 空闲连接对象是5
*/
protected int poolMaximumIdleConnections = 5;
/**
* 连接池的检出的时间是2s
*/
protected int poolMaximumCheckoutTime = 20000;
/**
* 连接池超时时间为2s
*/
protected int poolTimeToWait = 20000;
/**
* 可以容忍最大本地连接失败是3次
*/
protected int poolMaximumLocalBadConnectionTolerance = 3;
/**
* 连接池ping查询
*/
protected String poolPingQuery = "NO PING QUERY SET";
/**
* 开始连接池ping查询
*/
protected boolean poolPingEnabled;
/**
* 连接对象没有被使用之后，需要ping 数据库的时间间隔
*
*/
protected int poolPingConnectionsNotUsedFor;
/**
* 希望连接类型code，其实就是url+username+password 提取hashCode
*/
private int expectedConnectionTypeCode;
/**
* 创建一个无参函数
* PooledDataSource与UnpooledDataSource区别？
*
*/
public PooledDataSource() {
dataSource = new UnpooledDataSource();
}
/**
* 有一个参数的构造函数，UnpooledDataSource
* @param dataSource
*/
public PooledDataSource(UnpooledDataSource dataSource) {
this.dataSource = dataSource;
}
/**
* 将用完的连接对象放回连接池
* @param conn
* @throws SQLException
*/
protected void pushConnection(PooledConnection conn) throws SQLException {
synchronized (state) {
//从当前活动线程取出该连接对象
//如果有效
state.activeConnections.remove(conn);
if (conn.isValid()) {
//当前空闲连接对象的大小小于最大限制空闲连接数，且是当前用户名和密码登录连接池
//统计累积检出时间
//如果连接不是自动提交将手动调用rollback()方法
//重新创建连接对象，并将它加入到空闲集合中
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);
//设置当前时间戳为上一个连接的时间创建时间戳
//最后使用的时间戳也是修改一下（其实应该说重新用PooledConnection 包一下老的Connection）
//设置老connection无效
//唤醒其他线程
newConn.setCreatedTimestamp(conn.getCreatedTimestamp());
newConn.setLastUsedTimestamp(conn.getLastUsedTimestamp());
conn.invalidate();
if (log.isDebugEnabled()) {
log.debug("Returned connection " + newConn.getRealHashCode() + " to pool.");
}
state.notifyAll();
} else {
//空闲线程已经够了
// 累积线程检出时间
// 如果连接不是自动提交，就手动提交回滚
//关闭连接对象
//设置无效连接对象
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 {
//不是有效连接对象被遗弃
//同时统计无效连接数据
if (log.isDebugEnabled()) {
log.debug("A bad connection (" + conn.getRealHashCode() + ") attempted to return to the pool, discarding connection.");
}
state.badConnectionCount++;
}
}
}
/**
* 从数据库中拿出一个连接代理Connection对象
* @param username 用户名
* @param password 密码
* @return
* @throws SQLException
*/
private PooledConnection popConnection(String username, String password) throws SQLException {
//计数等待
//定义变量conn
//本地失败连接对象计数
boolean countedWait = false;
PooledConnection conn = null;
long t = System.currentTimeMillis();
int localBadConnectionCount = 0;
//从连接池获取连接对象
//同步state对象
while (conn == null) {
synchronized (state) {
//说明有空闲连接池对象
if (!state.idleConnections.isEmpty()) {
// Pool has available connection， 移除第一个索引位置连接对象，返回
conn = state.idleConnections.remove(0);
if (log.isDebugEnabled()) {
log.debug("Checked out connection " + conn.getRealHashCode() + " from pool.");
}
} else {
// Pool does not have available connection 没有空闲对象
// 判断当前活动线程是否大于最大活动线程，没有则可以创建
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
// 不能创建新的信息（已经是最大活动连接数）获取活动连接数激活时间最长的连接对象
//获取检出数据时间
// 当前时间大于最大检出时间，认为过期（也就是这个线程有问题）
PooledConnection oldestActiveConnection = state.activeConnections.get(0);
long longestCheckoutTime = oldestActiveConnection.getCheckoutTime();
if (longestCheckoutTime > poolMaximumCheckoutTime) {
// Can claim overdue connection
// 声明连接过期连接数++
// 累积检出过期连接对象
// 累积检出时间
// 移除当前老的对象
// 不是自动提交模式，调用对象的回滚操作
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");
}
}
// 获取连接对象
// 设置当前时间戳
// 设置上次使用时间戳
// 标记无效
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 {
//连接池不够用，需要等待了
// Must wait
try {
// 等待计数，需要等待poolTimeToWait（2s)时间
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
// 判断连接对象是否有效
if (conn.isValid()) {
//如果不是自动提交模式，调用回滚
//
if (!conn.getRealConnection().getAutoCommit()) {
conn.getRealConnection().rollback();
}
//设置连接hashcode
conn.setConnectionTypeCode(assembleConnectionTypeCode(dataSource.getUrl(), username, password));
//设置检出时间
conn.setCheckoutTimestamp(System.currentTimeMillis());
//设置上一次使用时间
//添加到激活连对象中
//请求数++
//计数累积请求时间
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.");
}
// 没有获取连接对象， 异常++
state.badConnectionCount++;
localBadConnectionCount++;
conn = null;
//本次失败次数 > 最大空闲数量+最大单次失败次数，抛出异常（默认是9次
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.");
}
}
}
}
}
// 为啥conn会为null
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;
}
/**
* 检查是否可用， ping操作
* Method to check to see if a connection is still usable
*
* @param conn - the connection to check
* @return True if the connection is still usable
*/
protected boolean pingConnection(PooledConnection conn) {
boolean result = true;
//判断connection本身是否关闭了
try {
result = !conn.getRealConnection().isClosed();
} catch (SQLException e) {
if (log.isDebugEnabled()) {
log.debug("Connection " + conn.getRealHashCode() + " is BAD: " + e.getMessage());
}
result = false;
}
//未关闭操作
//是否开启ping操作
if (result) {
if (poolPingEnabled) {
// 这个离上一次使用时间到现在时间段已经大于ping设置间隔时间
if (poolPingConnectionsNotUsedFor >= 0 && conn.getTimeElapsedSinceLastUse() > poolPingConnectionsNotUsedFor) {
try {
if (log.isDebugEnabled()) {
log.debug("Testing connection " + conn.getRealHashCode() + " ...");
}
//获取真实对象
//执行sql语句，然后关闭
//如果抛出异常说明ping有问题
Connection realConn = conn.getRealConnection();
try (Statement statement = realConn.createStatement()) {
statement.executeQuery(poolPingQuery).close();
}
if (!realConn.getAutoCommit()) {
realConn.rollback();
}
result = true;
if (log.isDebugEnabled()) {
log.debug("Connection " + conn.getRealHashCode() + " is GOOD!");
}
} catch (Exception e) {
log.warn("Execution of ping query '" + poolPingQuery + "' failed: " + e.getMessage());
//关闭连接对象
try {
conn.getRealConnection().close();
} catch (Exception e2) {
//ignore
}
result = false;
if (log.isDebugEnabled()) {
log.debug("Connection " + conn.getRealHashCode() + " is BAD: " + e.getMessage());
}
}
}
}
}
return result;
}
}
4.1、总结
- 这里关键方法就是popConnection,从连接池中取出连接对象，pushConnection将用完连接对象放回连接池，pingConnection判断连接对象是否有效
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