[译]JMS 消息优先级
我们将通过示例详细讨论 JMS 消息优先级。每条消息的标头字段代表其优先级。我在消息模型教程JMSPriority中讨论过消息优先级。
JMS 有 10 个优先级，从 0 到 9。0 是最低优先级，9 是最高优先级。根据 JMS 标准，优先级为 0-4 的消息为正常优先级，优先级为 5-9 的消息被视为加急优先级。
JMS 优先级示例
在下面的例子中，具有不同优先级的消息被发送给接收方。但是，优先级最高的消息（9）最先到达，同样，优先级最低的消息最后到达。
package lab01.message.model;
import labxx.common.settings.CommonSettings;
import javax.jms.*;
public class MessagePriorityTest {
public static void main(String[] args) throws JMSException {
ConnectionFactory connectionFactory = CommonSettings.getConnectionFactory();
Queue queue = CommonSettings.getDefaultQueue();
try (JMSContext jmsContext = connectionFactory.createContext()) {
JMSProducer producer = jmsContext.createProducer();
String[] messages = {"Msg One", "Msg two", "Msg three", "Msg four", "Msg five"};
producer.setPriority(0).send(queue, messages[0]);
producer.setPriority(9).send(queue, messages[1]);
producer.setPriority(4).send(queue, messages[2]);
producer.setPriority(2).send(queue, messages[3]);
producer.send(queue, messages[4]);
JMSConsumer consumer = jmsContext.createConsumer(queue);
for (int i = 0; i < messages.length; i++) {
Message message = consumer.receive();
System.out.println("Priority: " + message.getJMSPriority() + " #### Message: " + message.getBody(String.class));
}
}
}
}
输出
Priority: 9 #### Message: Msg two
Priority: 4 #### Message: Msg three
Priority: 2 #### Message: Msg four
Priority: 2 #### Message: Msg five
Priority: 0 #### Message: Msg One
JMS 消息默认优先级
即使您不指定消息优先级，JMS 也会为每条消息分配一个默认优先级。查看下面的代码示例，您可以在输出中看到每条消息的优先级为 4。
package lab01.message.model;
import labxx.common.settings.CommonSettings;
import javax.jms.*;
public class MessageDefaultPriorityTest {
public static void main(String[] args) throws JMSException {
ConnectionFactory connectionFactory = CommonSettings.getConnectionFactory();
Queue queue = CommonSettings.getDefaultQueue();
try (JMSContext jmsContext = connectionFactory.createContext()) {
JMSProducer producer = jmsContext.createProducer();
String[] messages = {"Msg One", "Msg two", "Msg three", "Msg four", "Msg five"};
producer.send(queue, messages[0]);
producer.send(queue, messages[1]);
producer.send(queue, messages[2]);
producer.send(queue, messages[3]);
producer.send(queue, messages[4]);
JMSConsumer consumer = jmsContext.createConsumer(queue);
for (int i = 0; i < messages.length; i++) {
Message message = consumer.receive();
System.out.println("Default Priority: " + message.getJMSPriority() + " #### Message: " + message.getBody(String.class));
}
}
}
}
输出
Default Priority: 4 #### Message: Msg One
Default Priority: 4 #### Message: Msg two
Default Priority: 4 #### Message: Msg three
Default Priority: 4 #### Message: Msg four
Default Priority: 4 #### Message: Msg five
这些都是 JMS 优先级消息的一部分，您已经了解了如何分配自定义优先级来控制消息传递。