ResourceHolderSupport

资源Holder父类。它有以下几个属性
  synchronizedWithTransaction 当Holder被注册到同步之后，为true,否则为false;同步处理完成之后，synchronizedWithTransaction被重新设置为false
  rollbackOnly 设置事务只读模式，JDBC并没有提供像JTA UserTransaction 的setRollbackOnly方法，所以在此增加这个属性标志底层事务回滚，Spring里叫GlobalRollbackOnly。当Spring事务提交时，会检查！shouldCommitOnGlobalRollbackOnly和GlobalRollbackOnly,如果都为真，（含义为全局会滚的时候不执行提交操作）然后会处理回滚，同时会根据事务是最外层事务或内层事务但标志是FailEarlyOnGlobalRollbackOnly，抛出异常，给事务发起者
  deadline 事务结束时间，如果设置了该值，则应用它到每条查询语句Statement
  referenceCount 一个Holder被请求和释放次数的计数器，如果请求次大于释放次，则referenceCount>0,通过此条件将用于判断该Holder是否被引用；如果没有，则释放掉Holder连接
  isVoid 标识资源是否为空，如果为true当绑定或解绑时，Holder返回null即不可获取.实际意义不大

/*
 * Copyright 2002-2008 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.transaction.support;

import java.util.Date;

import org.springframework.transaction.TransactionTimedOutException;

/**
 * Convenient base class for resource holders.
 *
 * <p>Features rollback-only support for nested transactions.
 * Can expire after a certain number of seconds or milliseconds,
 * to determine transactional timeouts.
 *
 * @author Juergen Hoeller
 * @since 02.02.2004
 * @see org.springframework.jdbc.datasource.DataSourceTransactionManager#doBegin
 * @see org.springframework.jdbc.datasource.DataSourceUtils#applyTransactionTimeout
 */
public abstract class ResourceHolderSupport implements ResourceHolder {

	private boolean synchronizedWithTransaction = false;

	private boolean rollbackOnly = false;

	private Date deadline;

	private int referenceCount = 0;

	private boolean isVoid = false;


	/**
	 * Mark the resource as synchronized with a transaction.
	 */
	public void setSynchronizedWithTransaction(boolean synchronizedWithTransaction) {
		this.synchronizedWithTransaction = synchronizedWithTransaction;
	}

	/**
	 * Return whether the resource is synchronized with a transaction.
	 */
	public boolean isSynchronizedWithTransaction() {
		return this.synchronizedWithTransaction;
	}

	/**
	 * Mark the resource transaction as rollback-only.
	 */
	public void setRollbackOnly() {
		this.rollbackOnly = true;
	}

	/**
	 * Return whether the resource transaction is marked as rollback-only.
	 */
	public boolean isRollbackOnly() {
		return this.rollbackOnly;
	}

	/**
	 * Set the timeout for this object in seconds.
	 * @param seconds number of seconds until expiration
	 */
	public void setTimeoutInSeconds(int seconds) {
		setTimeoutInMillis(seconds * 1000);
	}

	/**
	 * Set the timeout for this object in milliseconds.
	 * @param millis number of milliseconds until expiration
	 */
	public void setTimeoutInMillis(long millis) {
		this.deadline = new Date(System.currentTimeMillis() + millis);
	}

	/**
	 * Return whether this object has an associated timeout.
	 */
	public boolean hasTimeout() {
		return (this.deadline != null);
	}

	/**
	 * Return the expiration deadline of this object.
	 * @return the deadline as Date object
	 */
	public Date getDeadline() {
		return this.deadline;
	}

	/**
	 * Return the time to live for this object in seconds.
	 * Rounds up eagerly, e.g. 9.00001 still to 10.
	 * @return number of seconds until expiration
	 * @throws TransactionTimedOutException if the deadline has already been reached
	 */
	public int getTimeToLiveInSeconds() {
		double diff = ((double) getTimeToLiveInMillis()) / 1000;
		int secs = (int) Math.ceil(diff);
		checkTransactionTimeout(secs <= 0);
		return secs;
	}

	/**
	 * Return the time to live for this object in milliseconds.
	 * @return number of millseconds until expiration
	 * @throws TransactionTimedOutException if the deadline has already been reached
	 */
	public long getTimeToLiveInMillis() throws TransactionTimedOutException{
		if (this.deadline == null) {
			throw new IllegalStateException("No timeout specified for this resource holder");
		}
		long timeToLive = this.deadline.getTime() - System.currentTimeMillis();
		checkTransactionTimeout(timeToLive <= 0);
		return timeToLive;
	}

	/**
	 * Set the transaction rollback-only if the deadline has been reached,
	 * and throw a TransactionTimedOutException.
	 */
	private void checkTransactionTimeout(boolean deadlineReached) throws TransactionTimedOutException {
		if (deadlineReached) {
			setRollbackOnly();
			throw new TransactionTimedOutException("Transaction timed out: deadline was " + this.deadline);
		}
	}

	/**
	 * Increase the reference count by one because the holder has been requested
	 * (i.e. someone requested the resource held by it).
	 */
	public void requested() {
		this.referenceCount++;
	}

	/**
	 * Decrease the reference count by one because the holder has been released
	 * (i.e. someone released the resource held by it).
	 */
	public void released() {
		this.referenceCount--;
	}

	/**
	 * Return whether there are still open references to this holder.
	 */
	public boolean isOpen() {
		return (this.referenceCount > 0);
	}

	/**
	 * Clear the transactional state of this resource holder.
	 */
	public void clear() {
		this.synchronizedWithTransaction = false;
		this.rollbackOnly = false;
		this.deadline = null;
	}

	/**
	 * Reset this resource holder - transactional state as well as reference count.
	 */
	public void reset() {
		clear();
		this.referenceCount = 0;
	}

	public void unbound() {
		this.isVoid = true;
	}

	public boolean isVoid() {
		return this.isVoid;
	}

}