jdbc-getConnections()源码分析
源码位置： tomcat-jdbc:8.5.5
org.apache.tomcat.jdbc.pool.ConnectionPool.java
getConnection()
/**
* Borrows a connection from the pool. If a connection is available (in the
* idle queue) or the pool has not reached {@link PoolProperties#maxActive
* maxActive} connections a connection is returned immediately. If no
* connection is available, the pool will attempt to fetch a connection for
* {@link PoolProperties#maxWait maxWait} milliseconds.
* @param username The user name to use for the connection
* @param password The password for the connection
* @return Connection - a java.sql.Connection/javax.sql.PooledConnection
* reflection proxy, wrapping the underlying object.
* @throws SQLException
* - if the wait times out or a failure occurs creating a
* connection
*/
public Connection getConnection(String username, String password) throws SQLException {
// check out a connection
PooledConnection con = borrowConnection(-1, username, password);
return setupConnection(con);
}
相关属性
/**
* Carries the size of the pool, instead of relying on a queue implementation
* that usually iterates over to get an exact count
*/
private AtomicInteger size = new AtomicInteger(0);
/**
* Contains all the idle connections
*/
private BlockingQueue<PooledConnection> idle;
/**
* Contains all the connections that are in use
* TODO - this shouldn't be a blocking queue, simply a list to hold our objects
*/
private BlockingQueue<PooledConnection> busy;
从pools中获取Connection的实现
- 检查连接池是否关闭
- 尝试从idle中获取Connection，成功则返回，失败则继续执行；
- 判断Connection数是否达到
maxActive个，没有的话则创建新Connection； - 若Connection个数已经达到
maxActive个，则等待MaxWait时间后再从idle队列中获取Connection，并增加等待个数计数； - 超时等待后若还没有获取到，则抛出异常；
/**
* Thread safe way to retrieve a connection from the pool
* @param wait - time to wait, overrides the maxWait from the properties,
* set to -1 if you wish to use maxWait, 0 if you wish no wait time.
* @param username The user name to use for the connection
* @param password The password for the connection
* @return a connection
* @throws SQLException Failed to get a connection
*/
private PooledConnection borrowConnection(int wait, String username, String password) throws SQLException {
if (isClosed()) {
throw new SQLException("Connection pool closed.");
} //end if
//get the current time stamp
long now = System.currentTimeMillis();
//see if there is one available immediately
PooledConnection con = idle.poll();
while (true) {
if (con!=null) {
//configure the connection and return it
PooledConnection result = borrowConnection(now, con, username, password);
if (result!=null) return result;
}
//if we get here, see if we need to create one
//this is not 100% accurate since it doesn't use a shared
//atomic variable - a connection can become idle while we are creating
//a new connection
if (size.get() < getPoolProperties().getMaxActive()) {
//atomic duplicate check
if (size.addAndGet(1) > getPoolProperties().getMaxActive()) {
//if we got here, two threads passed through the first if
size.decrementAndGet();
} else {
//create a connection, we're below the limit
return createConnection(now, con, username, password);
}
} //end if
//calculate wait time for this iteration
long maxWait = wait;
//if the passed in wait time is -1, means we should use the pool property value
if (wait==-1) {
maxWait = (getPoolProperties().getMaxWait()<=0)?Long.MAX_VALUE:getPoolProperties().getMaxWait();
}
long timetowait = Math.max(0, maxWait - (System.currentTimeMillis() - now));
waitcount.incrementAndGet();
try {
//retrieve an existing connection
con = idle.poll(timetowait, TimeUnit.MILLISECONDS);
} catch (InterruptedException ex) {
if (getPoolProperties().getPropagateInterruptState()) {
Thread.currentThread().interrupt();
}
SQLException sx = new SQLException("Pool wait interrupted.");
sx.initCause(ex);
throw sx;
} finally {
waitcount.decrementAndGet();
}
if (maxWait==0 && con == null) { //no wait, return one if we have one
if (jmxPool!=null) {
jmxPool.notify(org.apache.tomcat.jdbc.pool.jmx.ConnectionPool.POOL_EMPTY, "Pool empty - no wait.");
}
throw new PoolExhaustedException("[" + Thread.currentThread().getName()+"] " +
"NoWait: Pool empty. Unable to fetch a connection, none available["+busy.size()+" in use].");
}
//we didn't get a connection, lets see if we timed out
if (con == null) {
if ((System.currentTimeMillis() - now) >= maxWait) {
if (jmxPool!=null) {
jmxPool.notify(org.apache.tomcat.jdbc.pool.jmx.ConnectionPool.POOL_EMPTY, "Pool empty - timeout.");
}
throw new PoolExhaustedException("[" + Thread.currentThread().getName()+"] " +
"Timeout: Pool empty. Unable to fetch a connection in " + (maxWait / 1000) +
" seconds, none available[size:"+size.get() +"; busy:"+busy.size()+"; idle:"+idle.size()+"; lastwait:"+timetowait+"].");
} else {
//no timeout, lets try again
continue;
}
}
} //while
}
borrowConnection：获取一个Connection
将Connection从idle队列存入到busy队列。
- 判断Connection是否已经释放，判断是否需要reconnection
MaxAge属性：当超过maxAge毫秒后，会强制重新连接；- 将该Connection存入busy队列；
/**
* Validates and configures a previously idle connection
* @param now - timestamp
* @param con - the connection to validate and configure
* @param username The user name to use for the connection
* @param password The password for the connection
* @return a connection
* @throws SQLException if a validation error happens
*/
protected PooledConnection borrowConnection(long now, PooledConnection con, String username, String password) throws SQLException {
//we have a connection, lets set it up
//flag to see if we need to nullify
boolean setToNull = false;
try {
con.lock();
if (con.isReleased()) {
return null;
}
//evaluate username/password change as well as max age functionality
boolean forceReconnect = con.shouldForceReconnect(username, password) || con.isMaxAgeExpired();
if (!con.isDiscarded() && !con.isInitialized()) {
//here it states that the connection not discarded, but the connection is null
//don't attempt a connect here. It will be done during the reconnect.
forceReconnect = true;
}
if (!forceReconnect) {
if ((!con.isDiscarded()) && con.validate(PooledConnection.VALIDATE_BORROW)) {
//set the timestamp
con.setTimestamp(now);
if (getPoolProperties().isLogAbandoned()) {
//set the stack trace for this pool
con.setStackTrace(getThreadDump());
}
if (!busy.offer(con)) {
log.debug("Connection doesn't fit into busy array, connection will not be traceable.");
}
return con;
}
}
//if we reached here, that means the connection
//is either has another principal, is discarded or validation failed.
//we will make one more attempt
//in order to guarantee that the thread that just acquired
//the connection shouldn't have to poll again.
try {
con.reconnect();
int validationMode = getPoolProperties().isTestOnConnect() || getPoolProperties().getInitSQL()!=null ?
PooledConnection.VALIDATE_INIT :
PooledConnection.VALIDATE_BORROW;
if (con.validate(validationMode)) {
//set the timestamp
con.setTimestamp(now);
if (getPoolProperties().isLogAbandoned()) {
//set the stack trace for this pool
con.setStackTrace(getThreadDump());
}
if (!busy.offer(con)) {
log.debug("Connection doesn't fit into busy array, connection will not be traceable.");
}
return con;
} else {
//validation failed.
throw new SQLException("Failed to validate a newly established connection.");
}
} catch (Exception x) {
release(con);
setToNull = true;
if (x instanceof SQLException) {
throw (SQLException)x;
} else {
SQLException ex = new SQLException(x.getMessage());
ex.initCause(x);
throw ex;
}
}
} finally {
con.unlock();
if (setToNull) {
con = null;
}
}
}
createConnection()：创建一个新Connection
创建一个Connection，并将其存入到 busy 队列中；
/**
* Creates a JDBC connection and tries to connect to the database.
* @param now timestamp of when this was called
* @param notUsed Argument not used
* @param username The user name to use for the connection
* @param password The password for the connection
* @return a PooledConnection that has been connected
* @throws SQLException Failed to get a connection
*/
protected PooledConnection createConnection(long now, PooledConnection tUsed, String username, String password) throws SQLException {
//no connections where available we'll create one
PooledConnection con = create(false);
if (username!=null) con.getAttributes().put(oledConnection.PROP_USER, username);
if (password!=null) con.getAttributes().put(oledConnection.PROP_PASSWORD, password);
boolean error = false;
try {
//connect and validate the connection
con.lock();
con.connect();
if (con.validate(PooledConnection.VALIDATE_INIT)) {
//no need to lock a new one, its not contented
con.setTimestamp(now);
if (getPoolProperties().isLogAbandoned()) {
con.setStackTrace(getThreadDump());
}
if (!busy.offer(con)) {
log.debug("Connection doesn't fit into busy array, nnection will not be traceable.");
}
return con;
} else {
//validation failed, make sure we disconnect
//and clean up
throw new SQLException("Validation Query Failed, enable gValidationErrors for more details.");
} //end if
} catch (Exception e) {
error = true;
if (log.isDebugEnabled())
log.debug("Unable to create a new JDBC connection.", e);
if (e instanceof SQLException) {
throw (SQLException)e;
} else {
SQLException ex = new SQLException(e.getMessage());
ex.initCause(e);
throw ex;
}
} finally {
// con can never be null here
if (error ) {
release(con);
}
con.unlock();
}//catch
}