在一次請求內繫結一個Session到執行緒，防止Web資源載入時的懶載入問題。HibernateTransactionManager或JTATransactionManager將會使用此Session。非事務執行時（並非事務掛起）也可使用。
該類的flushMode設定為Manual，由於該類一般為事務層提供Session，當Session同步到事務，對於非只讀事務(definition指定)由HibernateTransactionManager或SessionFactoryUtils改變flushMode為Auto。如果不在Spring提供事務環境下使用此類，則合理的設定flushMode
singleSession是否在整個請求中使用一個Session，還是每個事務塊或操作快使用一個Session，true說明整個請求使用一個Session。對於單個Session來說它從分利用了一級快取，缺點在於部分的事務失敗或訪問失敗，整個Session必須被廢棄；每個事務塊或操作快使用一個Session，對事務回滾或方位失敗都是可以由應用程式控制重新發起一次事務，同時開相應的Session，當然缺點在於增加了記憶體消耗。對非單個Session模式來說，延遲載入也是支援的，它使用延遲關閉Session策略。
具體實現上
單個Session：Filter或Interceptor負責開Session和繫結SessionHolder到當前執行緒供整個請求使用，渲染頁面之後關閉Session
每個事務或操作塊（HibernateTemplate,HibernateInterceptor）一個Session:Filter或Interceptor負責標識SessionFactory延遲，每個事務或操作塊會在代理實現中開啟一個Session同時處理具體代理操作之後將新開的Session新增到SessionFactory對應的延遲戴處理的集合中，渲染頁面之後關閉該SessionFactory對應的Session集合。
/*
* Copyright 2002-2012 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.orm.hibernate3.support;
import java.io.IOException;
import java.util.concurrent.Callable;
import javax.servlet.FilterChain;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.hibernate.FlushMode;
import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.springframework.dao.DataAccessResourceFailureException;
import org.springframework.orm.hibernate3.SessionFactoryUtils;
import org.springframework.orm.hibernate3.SessionHolder;
import org.springframework.transaction.support.TransactionSynchronizationManager;
import org.springframework.util.Assert;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.context.request.async.CallableProcessingInterceptorAdapter;
import org.springframework.web.context.request.async.WebAsyncManager;
import org.springframework.web.context.request.async.WebAsyncUtils;
import org.springframework.web.context.support.WebApplicationContextUtils;
import org.springframework.web.filter.OncePerRequestFilter;
/**
* Servlet 2.3 Filter that binds a Hibernate Session to the thread for the entire
* processing of the request. Intended for the "Open Session in View" pattern,
* i.e. to allow for lazy loading in web views despite the original transactions
* already being completed.
*
* <p>This filter makes Hibernate Sessions available via the current thread, which
* will be autodetected by transaction managers. It is suitable for service layer
* transactions via {@link org.springframework.orm.hibernate3.HibernateTransactionManager}
* or {@link org.springframework.transaction.jta.JtaTransactionManager} as well
* as for non-transactional execution (if configured appropriately).
*
* <p><b>NOTE</b>: This filter will by default <i>not</i> flush the Hibernate Session,
* with the flush mode set to {@code FlushMode.NEVER}. It assumes to be used
* in combination with service layer transactions that care for the flushing: The
* active transaction manager will temporarily change the flush mode to
* {@code FlushMode.AUTO} during a read-write transaction, with the flush
* mode reset to {@code FlushMode.NEVER} at the end of each transaction.
* If you intend to use this filter without transactions, consider changing
* the default flush mode (through the "flushMode" property).
*
* <p><b>WARNING:</b> Applying this filter to existing logic can cause issues that
* have not appeared before, through the use of a single Hibernate Session for the
* processing of an entire request. In particular, the reassociation of persistent
* objects with a Hibernate Session has to occur at the very beginning of request
* processing, to avoid clashes with already loaded instances of the same objects.
*
* <p>Alternatively, turn this filter into deferred close mode, by specifying
* "singleSession"="false": It will not use a single session per request then,
* but rather let each data access operation or transaction use its own session
* (like without Open Session in View). Each of those sessions will be registered
* for deferred close, though, actually processed at request completion.
*
* <p>A single session per request allows for most efficient first-level caching,
* but can cause side effects, for example on {@code saveOrUpdate} or when
* continuing after a rolled-back transaction. The deferred close strategy is as safe
* as no Open Session in View in that respect, while still allowing for lazy loading
* in views (but not providing a first-level cache for the entire request).
*
* <p>Looks up the SessionFactory in Spring's root web application context.
* Supports a "sessionFactoryBeanName" filter init-param in {@code web.xml};
* the default bean name is "sessionFactory". Looks up the SessionFactory on each
* request, to avoid initialization order issues (when using ContextLoaderServlet,
* the root application context will get initialized <i>after</i> this filter).
*
* @author Juergen Hoeller
* @since 1.2
* @see #setSingleSession
* @see #setFlushMode
* @see #lookupSessionFactory
* @see OpenSessionInViewInterceptor
* @see org.springframework.orm.hibernate3.HibernateInterceptor
* @see org.springframework.orm.hibernate3.HibernateTransactionManager
* @see org.springframework.orm.hibernate3.SessionFactoryUtils#getSession
* @see org.springframework.transaction.support.TransactionSynchronizationManager
*/
public class OpenSessionInViewFilter extends OncePerRequestFilter {
public static final String DEFAULT_SESSION_FACTORY_BEAN_NAME = "sessionFactory";
private String sessionFactoryBeanName = DEFAULT_SESSION_FACTORY_BEAN_NAME;
private boolean singleSession = true;
private FlushMode flushMode = FlushMode.MANUAL;
/**
* Set the bean name of the SessionFactory to fetch from Spring's
* root application context. Default is "sessionFactory".
* @see #DEFAULT_SESSION_FACTORY_BEAN_NAME
*/
public void setSessionFactoryBeanName(String sessionFactoryBeanName) {
this.sessionFactoryBeanName = sessionFactoryBeanName;
}
/**
* Return the bean name of the SessionFactory to fetch from Spring's
* root application context.
*/
protected String getSessionFactoryBeanName() {
return this.sessionFactoryBeanName;
}
/**
* Set whether to use a single session for each request. Default is "true".
* <p>If set to "false", each data access operation or transaction will use
* its own session (like without Open Session in View). Each of those
* sessions will be registered for deferred close, though, actually
* processed at request completion.
* @see SessionFactoryUtils#initDeferredClose
* @see SessionFactoryUtils#processDeferredClose
*/
public void setSingleSession(boolean singleSession) {
this.singleSession = singleSession;
}
/**
* Return whether to use a single session for each request.
*/
protected boolean isSingleSession() {
return this.singleSession;
}
/**
* Specify the Hibernate FlushMode to apply to this filter's
* {@link org.hibernate.Session}. Only applied in single session mode.
* <p>Can be populated with the corresponding constant name in XML bean
* definitions: e.g. "AUTO".
* <p>The default is "MANUAL". Specify "AUTO" if you intend to use
* this filter without service layer transactions.
* @see org.hibernate.Session#setFlushMode
* @see org.hibernate.FlushMode#MANUAL
* @see org.hibernate.FlushMode#AUTO
*/
public void setFlushMode(FlushMode flushMode) {
this.flushMode = flushMode;
}
/**
* Return the Hibernate FlushMode that this filter applies to its
* {@link org.hibernate.Session} (in single session mode).
*/
protected FlushMode getFlushMode() {
return this.flushMode;
}
/**
* The default value is "false" so that the filter may re-bind the opened
* {@code Session} to each asynchronously dispatched thread and postpone
* closing it until the very last asynchronous dispatch.
*/
@Override
protected boolean shouldNotFilterAsyncDispatch() {
return false;
}
/**
* Returns "false" so that the filter may provide a Hibernate
* {@code Session} to each error dispatches.
*/
@Override
protected boolean shouldNotFilterErrorDispatch() {
return false;
}
@Override
protected void doFilterInternal(
HttpServletRequest request, HttpServletResponse response, FilterChain filterChain)
throws ServletException, IOException {
SessionFactory sessionFactory = lookupSessionFactory(request);
boolean participate = false;
WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
String key = getAlreadyFilteredAttributeName();
if (isSingleSession()) {
// single session mode
if (TransactionSynchronizationManager.hasResource(sessionFactory)) {
// Do not modify the Session: just set the participate flag.
participate = true;
}
else {
boolean isFirstRequest = !isAsyncDispatch(request);
if (isFirstRequest || !applySessionBindingInterceptor(asyncManager, key)) {
logger.debug("Opening single Hibernate Session in OpenSessionInViewFilter");
Session session = getSession(sessionFactory);
SessionHolder sessionHolder = new SessionHolder(session);
TransactionSynchronizationManager.bindResource(sessionFactory, sessionHolder);
asyncManager.registerCallableInterceptor(key,
new SessionBindingCallableInterceptor(sessionFactory, sessionHolder));
}
}
}
else {
// deferred close mode
Assert.state(!isAsyncStarted(request), "Deferred close mode is not supported on async dispatches");
if (SessionFactoryUtils.isDeferredCloseActive(sessionFactory)) {
// Do not modify deferred close: just set the participate flag.
participate = true;
}
else {
SessionFactoryUtils.initDeferredClose(sessionFactory);
}
}
try {
filterChain.doFilter(request, response);
}
finally {
if (!participate) {
if (isSingleSession()) {
// single session mode
SessionHolder sessionHolder =
(SessionHolder) TransactionSynchronizationManager.unbindResource(sessionFactory);
if (!isAsyncStarted(request)) {
logger.debug("Closing single Hibernate Session in OpenSessionInViewFilter");
closeSession(sessionHolder.getSession(), sessionFactory);
}
}
else {
// deferred close mode
SessionFactoryUtils.processDeferredClose(sessionFactory);
}
}
}
}
/**
* Look up the SessionFactory that this filter should use,
* taking the current HTTP request as argument.
* <p>The default implementation delegates to the {@link #lookupSessionFactory()}
* variant without arguments.
* @param request the current request
* @return the SessionFactory to use
*/
protected SessionFactory lookupSessionFactory(HttpServletRequest request) {
return lookupSessionFactory();
}
/**
* Look up the SessionFactory that this filter should use.
* <p>The default implementation looks for a bean with the specified name
* in Spring's root application context.
* @return the SessionFactory to use
* @see #getSessionFactoryBeanName
*/
protected SessionFactory lookupSessionFactory() {
if (logger.isDebugEnabled()) {
logger.debug("Using SessionFactory '" + getSessionFactoryBeanName() + "' for OpenSessionInViewFilter");
}
WebApplicationContext wac = WebApplicationContextUtils.getRequiredWebApplicationContext(getServletContext());
return wac.getBean(getSessionFactoryBeanName(), SessionFactory.class);
}
/**
* Get a Session for the SessionFactory that this filter uses.
* Note that this just applies in single session mode!
* <p>The default implementation delegates to the
* {@code SessionFactoryUtils.getSession} method and
* sets the {@code Session}'s flush mode to "MANUAL".
* <p>Can be overridden in subclasses for creating a Session with a
* custom entity interceptor or JDBC exception translator.
* @param sessionFactory the SessionFactory that this filter uses
* @return the Session to use
* @throws DataAccessResourceFailureException if the Session could not be created
* @see org.springframework.orm.hibernate3.SessionFactoryUtils#getSession(SessionFactory, boolean)
* @see org.hibernate.FlushMode#MANUAL
*/
protected Session getSession(SessionFactory sessionFactory) throws DataAccessResourceFailureException {
Session session = SessionFactoryUtils.getSession(sessionFactory, true);
FlushMode flushMode = getFlushMode();
if (flushMode != null) {
session.setFlushMode(flushMode);
}
return session;
}
/**
* Close the given Session.
* Note that this just applies in single session mode!
* <p>Can be overridden in subclasses, e.g. for flushing the Session before
* closing it. See class-level javadoc for a discussion of flush handling.
* Note that you should also override getSession accordingly, to set
* the flush mode to something else than NEVER.
* @param session the Session used for filtering
* @param sessionFactory the SessionFactory that this filter uses
*/
protected void closeSession(Session session, SessionFactory sessionFactory) {
SessionFactoryUtils.closeSession(session);
}
private boolean applySessionBindingInterceptor(WebAsyncManager asyncManager, String key) {
if (asyncManager.getCallableInterceptor(key) == null) {
return false;
}
((SessionBindingCallableInterceptor) asyncManager.getCallableInterceptor(key)).initializeThread();
return true;
}
/**
* Bind and unbind the Hibernate {@code Session} to the current thread.
*/
private static class SessionBindingCallableInterceptor extends CallableProcessingInterceptorAdapter {
private final SessionFactory sessionFactory;
private final SessionHolder sessionHolder;
public SessionBindingCallableInterceptor(SessionFactory sessionFactory, SessionHolder sessionHolder) {
this.sessionFactory = sessionFactory;
this.sessionHolder = sessionHolder;
}
@Override
public <T> void preProcess(NativeWebRequest request, Callable<T> task) {
initializeThread();
}
@Override
public <T> void postProcess(NativeWebRequest request, Callable<T> task, Object concurrentResult) {
TransactionSynchronizationManager.unbindResource(this.sessionFactory);
}
private void initializeThread() {
TransactionSynchronizationManager.bindResource(this.sessionFactory, this.sessionHolder);
}
}
}