JMS结构
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1.ConnectionFactory

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A?ConnectionFactory?object encapsulates a set of connection configuration parameters that has been defined by an administrator. A client uses it to create a connection with a JMS provider.

A?ConnectionFactory?object is a JMS administered object and supports concurrent use.

JMS administered objects are objects containing configuration information that are created by an administrator and later used by JMS clients. They make it practical to administer the JMS API in the enterprise.

Although the interfaces for administered objects do not explicitly depend on the Java Naming and Directory Interface (JNDI) API, the JMS API establishes the convention that JMS clients find administered objects by looking them up in a JNDI namespace.

An administrator can place an administered object anywhere in a namespace. The JMS API does not define a naming policy.

It is expected that JMS providers will provide the tools an administrator needs to create and configure administered objects in a JNDI namespace. JMS provider implementations of administered objects should be both?javax.jndi.Referenceable?and?java.io.Serializable?so that they can be stored in all JNDI naming contexts. In addition, it is recommended that these implementations follow the JavaBeansTM?design patterns.

This strategy provides several benefits:

It hides provider-specific details from JMS clients.It abstracts administrative information into objects in the Java programming language ("Java objects") that are easily organized and administered from a common management console.Since there will be JNDI providers for all popular naming services, this means that JMS providers can deliver one implementation of administered objects that will run everywhere.

An administered object should not hold on to any remote resources. Its lookup should not use remote resources other than those used by the JNDI API itself.

Clients should think of administered objects as local Java objects. Looking them up should not have any hidden side effects or use surprising amounts of local resources.

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2.Connection

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A?Connection?object is a client's active connection to its JMS provider. It typically allocates provider resources outside the Java virtual machine (JVM).

Connections support concurrent use.

A connection serves several purposes:

It encapsulates an open connection with a JMS provider. It typically represents an open TCP/IP socket between a client and the service provider software.Its creation is where client authentication takes place.It can specify a unique client identifier.It provides a?ConnectionMetaData?object.It supports an optional?ExceptionListener?object.

Because the creation of a connection involves setting up authentication and communication, a connection is a relatively heavyweight object. Most clients will do all their messaging with a single connection. Other more advanced applications may use several connections. The JMS API does not architect a reason for using multiple connections; however, there may be operational reasons for doing so.

A JMS client typically creates a connection, one or more sessions, and a number of message producers and consumers. When a connection is created, it is in stopped mode. That means that no messages are being delivered.

It is typical to leave the connection in stopped mode until setup is complete (that is, until all message consumers have been created). At that point, the client calls the connection's?start?method, and messages begin arriving at the connection's consumers. This setup convention minimizes any client confusion that may result from asynchronous message delivery while the client is still in the process of setting itself up.

A connection can be started immediately, and the setup can be done afterwards. Clients that do this must be prepared to handle asynchronous message delivery while they are still in the process of setting up.

A message producer can send messages while a connection is stopped.

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From :java api

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3.Session

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public interface Sessionextends java.lang.Runnable

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A?Session?object is a single-threaded?(单线程)context for producing and consuming messages. Although it may allocate provider resources outside the Java virtual machine (JVM), it is considered a lightweight JMS object.

A session serves several purposes:

It is a factory for its message producers and consumers.It supplies provider-optimized message factories.It is a factory for?TemporaryTopics?and?TemporaryQueues.It provides a way to create?Queue?or?Topic?objects for those clients that need to dynamically manipulate provider-specific destination names.It supports a single series of transactions that combine work spanning its producers and consumers into atomic units.It defines a serial order for the messages it consumes and the messages it produces.It retains messages it consumes until they have been acknowledged.It serializes execution of message listeners registered with its message consumers.It is a factory for?QueueBrowsers.

A session can create and service multiple message producers and consumers.

One typical use is to have a thread block on a synchronous?MessageConsumer?until a message arrives. The thread may then use one or more of the?Session's?MessageProducers.

If a client desires to have one thread produce messages while others consume them, the client should use a separate session for its producing thread.

Once a connection has been started, any session with one or more registered message listeners is dedicated to the thread of control that delivers messages to it. It is erroneous for client code to use this session or any of its constituent objects from another thread of control. The only exception to this rule is the use of the session or connection?close?method.

It should be easy for most clients to partition their work naturally into sessions. This model allows clients to start simply and incrementally add message processing complexity as their need for concurrency grows.

The?close?method is the only session method that can be called while some other session method is being executed in another thread.

A session may be specified as transacted. Each transacted session supports a single series of transactions. Each transaction groups a set of message sends and a set of message receives into an atomic unit of work. In effect, transactions organize a session's input message stream and output message stream into series of atomic units. When a transaction commits, its atomic unit of input is acknowledged and its associated atomic unit of output is sent. If a transaction rollback is done, the transaction's sent messages are destroyed and the session's input is automatically recovered.

The content of a transaction's input and output units is simply those messages that have been produced and consumed within the session's current transaction.

A transaction is completed using either its session's?commit?method or its session's?rollback?method. The completion of a session's current transaction automatically begins the next. The result is that a transacted session always has a current transaction within which its work is done.

The Java Transaction Service (JTS) or some other transaction monitor may be used to combine a session's transaction with transactions on other resources (databases, other JMS sessions, etc.). Since Java distributed transactions are controlled via the Java Transaction API (JTA), use of the session's?commit?and?rollback?methods in this context is prohibited.

The JMS API does not require support for JTA; however, it does define how a provider supplies this support.

Although it is also possible for a JMS client to handle distributed transactions directly, it is unlikely that many JMS clients will do this. Support for JTA in the JMS API is targeted at systems vendors who will be integrating the JMS API into their application server products.

? ? ? ? 表示一个单线程的上下文，用于发送和接收消息。由于会话是单线程的，所以消息是连续的，就是说消息是按照发送的顺序一个一个接收的。会话的好处是它支持事务。如果用户选择了事务支持，会话上下文将保存一组消息，直到事务被提交才发送这些消息。在提交事务之前，用户可以使用回滚操作取消这些消息。一个会话允许用户创建消息生产者来发送消息，创建消息消费者来接收消息。

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4.MessageConsumer

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A client uses a?MessageConsumer?object to receive messages from a destination. A?MessageConsumer?object is created by passing a?Destination?object to a message-consumer creation method supplied by a session.

MessageConsumer?is the parent interface for all message consumers.

A message consumer can be created with a message selector. A message selector allows the client to restrict the messages delivered to the message consumer to those that match the selector.

A client may either synchronously receive a message consumer's messages or have the consumer asynchronously deliver them as they arrive.

For synchronous receipt, a client can request the next message from a message consumer using one of its?receive?methods. There are several variations of?receive?that allow a client to poll or wait for the next message.

For asynchronous delivery, a client can register a?MessageListener?object with a message consumer. As messages arrive at the message consumer, it delivers them by calling the?MessageListener's?onMessage?method.

It is a client programming error for a?MessageListener?to throw an exception.

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5.MessageProducer

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A client uses a?MessageProducer?object to send messages to a destination. A?MessageProducer?object is created by passing a?Destination?object to a message-producer creation method supplied by a session.

MessageProducer?is the parent interface for all message producers.

A client also has the option of creating a message producer without supplying a destination. In this case, a destination must be provided with every send operation. A typical use for this kind of message producer is to send replies to requests using the request's?JMSReplyTo?destination.

A client can specify a default delivery mode, priority, and time to live for messages sent by a message producer. It can also specify the delivery mode, priority, and time to live for an individual message.

A client can specify a time-to-live value in milliseconds for each message it sends. This value defines a message expiration time that is the sum of the message's time-to-live and the GMT when it is sent (for transacted sends, this is the time the client sends the message, not the time the transaction is committed).

A JMS provider should do its best to expire messages accurately; however, the JMS API does not define the accuracy provided.

Including:QueueSender,TopicPublisher

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6.Destination

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A?Destination?object encapsulates a provider-specific address. The JMS API does not define a standard address syntax. Although a standard address syntax was considered, it was decided that the differences in address semantics between existing message-oriented middleware (MOM) products were too wide to bridge with a single syntax.

Since?Destination?is an administered object, it may contain provider-specific configuration information in addition to its address.

The JMS API also supports a client's use of provider-specific address names.

Destination?objects support concurrent use.

A?Destination?object is a JMS administered object.

JMS administered objects are objects containing configuration information that are created by an administrator and later used by JMS clients. They make it practical to administer the JMS API in the enterprise.

Although the interfaces for administered objects do not explicitly depend on the Java Naming and Directory Interface (JNDI) API, the JMS API establishes the convention that JMS clients find administered objects by looking them up in a JNDI namespace.

An administrator can place an administered object anywhere in a namespace. The JMS API does not define a naming policy.

It is expected that JMS providers will provide the tools an administrator needs to create and configure administered objects in a JNDI namespace. JMS provider implementations of administered objects should implement the?javax.naming.Referenceable?and?java.io.Serializable?interfaces so that they can be stored in all JNDI naming contexts. In addition, it is recommended that these implementations follow the JavaBeansTM?design patterns.

This strategy provides several benefits:

It hides provider-specific details from JMS clients.It abstracts JMS administrative information into objects in the Java programming language ("Java objects") that are easily organized and administered from a common management console.Since there will be JNDI providers for all popular naming services, JMS providers can deliver one implementation of administered objects that will run everywhere.

An administered object should not hold on to any remote resources. Its lookup should not use remote resources other than those used by the JNDI API itself.

Clients should think of administered objects as local Java objects. Looking them up should not have any hidden side effects or use surprising amounts of local resources.

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I will continue to learn about the detail about the difference between TOPIC and QUEUE, and the defination of the Message.