huifer
5 years ago
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# Spring JmsTemplate
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- Author: [HuiFer](https://github.com/huifer)
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- 源码阅读仓库: [SourceHot-spring](https://github.com/SourceHot/spring-framework-read)
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- 源码路径: `org.springframework.jms.core.JmsTemplate`
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## 源码分析
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### send 发送消息
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```java
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@Override
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public void send(final String destinationName, final MessageCreator messageCreator) throws JmsException {
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// 执行.
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execute(session -> {
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Destination destination = resolveDestinationName(session, destinationName);
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doSend(session, destination, messageCreator);
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return null;
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}, false);
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}
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```
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```java
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@Nullable
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public <T> T execute(SessionCallback<T> action, boolean startConnection) throws JmsException {
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Assert.notNull(action, "Callback object must not be null");
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Connection conToClose = null;
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Session sessionToClose = null;
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try {
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Session sessionToUse = ConnectionFactoryUtils.doGetTransactionalSession(
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obtainConnectionFactory(), this.transactionalResourceFactory, startConnection);
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if (sessionToUse == null) {
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// 创建链接
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conToClose = createConnection();
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// 创建session
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sessionToClose = createSession(conToClose);
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if (startConnection) {
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conToClose.start();
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}
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sessionToUse = sessionToClose;
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}
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if (logger.isDebugEnabled()) {
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logger.debug("Executing callback on JMS Session: " + sessionToUse);
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}
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/**
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* sessionCallback 执行
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* {@link JmsTemplate#doSend(Session, javax.jms.Destination, org.springframework.jms.core.MessageCreator)}
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*/
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return action.doInJms(sessionToUse);
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} catch (JMSException ex) {
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throw convertJmsAccessException(ex);
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} finally {
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// 资源释放
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JmsUtils.closeSession(sessionToClose);
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ConnectionFactoryUtils.releaseConnection(conToClose, getConnectionFactory(), startConnection);
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}
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}
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```
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- 最后`action.doInJms(sessionToUse)`的操作
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```java
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Destination destination = resolveDestinationName(session, destinationName);
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doSend(session, destination, messageCreator);
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return null;
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```
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- `doSend`真正做的发送方法
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```java
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protected void doSend(Session session, Destination destination, MessageCreator messageCreator)
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throws JMSException {
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Assert.notNull(messageCreator, "MessageCreator must not be null");
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// 创建消息生产者
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MessageProducer producer = createProducer(session, destination);
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try {
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// 创建消息
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Message message = messageCreator.createMessage(session);
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if (logger.isDebugEnabled()) {
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logger.debug("Sending created message: " + message);
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}
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// 发送
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doSend(producer, message);
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// Check commit - avoid commit call within a JTA transaction.
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if (session.getTransacted() && isSessionLocallyTransacted(session)) {
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// Transacted session created by this template -> commit.
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JmsUtils.commitIfNecessary(session);
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}
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} finally {
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// 关闭消息生产者
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JmsUtils.closeMessageProducer(producer);
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}
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}
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```
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1. `createProducer`中通过`javax.jms.Session.createProducer`创建`MessageProducer`,第三方消息中间件独立实现
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2. `createMessage`
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```java
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@Override
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public javax.jms.Message createMessage(Session session) throws JMSException {
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try {
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// 消息转换
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return this.messageConverter.toMessage(this.message, session);
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} catch (Exception ex) {
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throw new MessageConversionException("Could not convert '" + this.message + "'", ex);
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}
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}
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```
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- 消息转换后续在更新
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3. `doSend` 这里也是第三方消息中间件实现
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```java
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protected void doSend(MessageProducer producer, Message message) throws JMSException {
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if (this.deliveryDelay >= 0) {
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producer.setDeliveryDelay(this.deliveryDelay);
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}
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if (isExplicitQosEnabled()) {
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// 发送消息,第三方消息中间件实现
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producer.send(message, getDeliveryMode(), getPriority(), getTimeToLive());
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} else {
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producer.send(message);
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}
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}
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```
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4. `closeMessageProducer` 这个方法特别,直接关闭
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```java
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public static void closeMessageProducer(@Nullable MessageProducer producer) {
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if (producer != null) {
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try {
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producer.close();
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} catch (JMSException ex) {
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logger.trace("Could not close JMS MessageProducer", ex);
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} catch (Throwable ex) {
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// We don't trust the JMS provider: It might throw RuntimeException or Error.
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logger.trace("Unexpected exception on closing JMS MessageProducer", ex);
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}
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}
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}
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```
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### receive 接收消息
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```java
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@Override
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@Nullable
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public Message receive(String destinationName) throws JmsException {
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return receiveSelected(destinationName, null);
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}
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@Override
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@Nullable
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public Message receiveSelected(final String destinationName, @Nullable final String messageSelector) throws JmsException {
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return execute(session -> {
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Destination destination = resolveDestinationName(session, destinationName);
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return doReceive(session, destination, messageSelector);
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}, true);
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}
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@Nullable
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protected Message doReceive(Session session, Destination destination, @Nullable String messageSelector)
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throws JMSException {
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return doReceive(session, createConsumer(session, destination, messageSelector));
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}
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@Nullable
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protected Message doReceive(Session session, MessageConsumer consumer) throws JMSException {
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try {
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// Use transaction timeout (if available).
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long timeout = getReceiveTimeout();
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// 链接工厂
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ConnectionFactory connectionFactory = getConnectionFactory();
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// JMS 资源信息
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JmsResourceHolder resourceHolder = null;
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if (connectionFactory != null) {
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// 从连接对象中获取JMS 资源信息
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resourceHolder = (JmsResourceHolder) TransactionSynchronizationManager.getResource(connectionFactory);
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}
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if (resourceHolder != null && resourceHolder.hasTimeout()) {
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// 超时时间
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timeout = Math.min(timeout, resourceHolder.getTimeToLiveInMillis());
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}
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// 具体的消息
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Message message = receiveFromConsumer(consumer, timeout);
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if (session.getTransacted()) {
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// 事务性操作
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// Commit necessary - but avoid commit call within a JTA transaction.
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if (isSessionLocallyTransacted(session)) {
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// Transacted session created by this template -> commit.
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JmsUtils.commitIfNecessary(session);
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}
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} else if (isClientAcknowledge(session)) {
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// Manually acknowledge message, if any.
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if (message != null) {
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message.acknowledge();
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}
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}
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return message;
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} finally {
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JmsUtils.closeMessageConsumer(consumer);
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}
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}
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```
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