OpenSessionInViewFilter线程绑定session

           我们知道OpenSessionInViewFilter是通过TransactionSynchronizationManager.bindResource(sessionFactory, new SessionHolder(session));来达到线程绑定的。

抽象类TransactionSynchronizationManager的一些主要属性和方法：

private static final ThreadLocal resources =
new NamedThreadLocal("Transactional resources");//保存了当前线程的session和Transactional信息


private static final ThreadLocal synchronizations =
new NamedThreadLocal("Transaction synchronizations");


private static final ThreadLocal currentTransactionName =
new NamedThreadLocal("Current transaction name");


private static final ThreadLocal currentTransactionReadOnly =
new NamedThreadLocal("Current transaction read-only status");


private static final ThreadLocal currentTransactionIsolationLevel =
new NamedThreadLocal("Current transaction isolation level");


private static final ThreadLocal actualTransactionActive =
new NamedThreadLocal("Actual transaction active");

public static void bindResource(Object key, Object value) throws IllegalStateException {//绑定session到当前线程Object actualKey = TransactionSynchronizationUtils.unwrapResourceIfNecessary(key);//去除包装Assert.notNull(value, "Value must not be null");Map map = (Map) resources.get();// set ThreadLocal Map if none foundif (map == null) {map = new HashMap();resources.set(map);}if (map.put(actualKey, value) != null) {throw new IllegalStateException("Already value [" + map.get(actualKey) + "] for key [" +actualKey + "] bound to thread [" + Thread.currentThread().getName() + "]");}if (logger.isTraceEnabled()) {logger.trace("Bound value [" + value + "] for key [" + actualKey + "] to thread [" +Thread.currentThread().getName() + "]");}}

public static Object unbindResource(Object key) throws IllegalStateException {//解绑当前线程的sessionObject actualKey = TransactionSynchronizationUtils.unwrapResourceIfNecessary(key);Object value = doUnbindResource(actualKey);if (value == null) {throw new IllegalStateException("No value for key [" + actualKey + "] bound to thread [" + Thread.currentThread().getName() + "]");}return value;}

public static boolean hasResource(Object key) {//判断当前线程是否已经绑定了session,key是sessionFactory对象,一个sessionFactory可以绑定一个sessionObject actualKey = TransactionSynchronizationUtils.unwrapResourceIfNecessary(key);Object value = doGetResource(actualKey);return (value != null);}

注意：Map map = (Map) resources.get();

public class ThreadLocal<T> ：

    public T get() {        Thread t = Thread.currentThread();        ThreadLocalMap map = getMap(t);        if (map != null) {            ThreadLocalMap.Entry e = map.getEntry(this);            if (e != null)                return (T)e.value;        }        return setInitialValue();    }

    ThreadLocalMap getMap(Thread t) {        return t.threadLocals;    }

    void createMap(Thread t, T firstValue) {        t.threadLocals = new ThreadLocalMap(this, firstValue);    }

将ThreadLocal<T>本身作为key，对应的泛型作为value