Using message properties_RabbitMQ Cookbook-QQ阅读男生中文科幻网

书名：RabbitMQ Cookbook
作者名：Sigismondo Boschi Gabriele Santomaggio
本章字数：531字
更新时间：2025-04-04 22:04:15

Using message properties

In this example we will show how an AMQP message is divided, and how to use message properties.

You can find the source at Chapter01/Recipe11/Java_11/.

Getting ready

To use this recipe you will need to set up the Java development environment as indicated in the Introduction section.

How to do it…

In order to access the message properties you need to perform the following steps:

Declare a queue:

channel.queueDeclare(MyQueue, false, false, false,null);

Create a BasicProperties class:

Map<String,Object>headerMap = new HashMap<String,   Object>();
headerMap.put("key1", "value1");
headerMap.put("key2", new Integer(50) );
headerMap.put("key3", new Boolean(false));
headerMap.put("key4", "value4");

BasicProperties messageProperties = new BasicProperties.Builder()
.timestamp(new Date())
.contentType("text/plain")
.userId("guest")
.appId("app id: 20")
.deliveryMode(1)
.priority(1)
.headers(headerMap)
.clusterId("cluster id: 1")
.build();

Publish a message with basic properties:

channel.basicPublish("",myQueue,messageProperties,message.getBytes())

Consume a message and print the properties:

System.out.println("Property:" + properties.toString());

How it works…

The AMQP message (also called content) is divided into two parts:

Content header
Content body (as we have already seen in previous examples)

In step 2 we create a content header using BasicProperties:

Map<String,Object>headerMap = new HashMap<String, Object>();
BasicProperties messageProperties = new BasicProperties.Builder()
.timestamp(new Date())
.userId("guest")  
.deliveryMode(1)
.priority(1)
.headers(headerMap)
.build();

With this object we have set up the following properties:

timestamp: This is the message time stamp.
userId: This is the broker with whom the user sends the message (by default, it is "guest"). In the next chapter we'll see the users' management.
deliveryMode: If set to 1 the message is nonpersistent, if it is 2 the message is persistent (you can see the recipe Connecting to the broker).
priority: This defines the message priority, which can be 0 to 9.
headers: A HashMap<String, Object> header, you are free to use it to enter your custom fields.

Tip

The RabbitMQ BasicProperties class is an AMQP content header implementation. The attribute of BasicProperties can be built using BasicProperties.Builder()

The header is ready and we can send a message using channel.basicPublish("",myQueue, messageProperties,message.getBytes()), where messageProperties is the message header and message is the message body.

In step 4 the consumer gets a message:

public void handleDelivery(String consumerTag,Envelope envelope, 
BasicProperties properties,byte[] body) throws java.io.IOException {
System.out.println("***********message header****************");
System.out.println("Message sent at:"+ properties.getTimestamp());
System.out.println("Message sent by user:"+ properties.getUserId());
System.out.println("Message sent by App:"+properties.getAppId());
System.out.println("all properties :" + properties.toString());
System.out.println("**********message body**************");
String message = new String(body);
System.out.println("Message Body:"+message);
}

The parameter properties contains the message header and body contains its body.

There's more…

Using message properties we can optimize the performance. Writing audit information or log information into the body is a typical error, because the consumer should parse the body to get them.

The body message must only contain application data (for example, a Book class), while the message properties can host other information related to the messaging mechanics or other implementation details.

For example, if the consumer wants to log when a message has been sent you can use the timestamp attribute, or if the consumer needs to distinguish a message according to a custom tag, you can put it in the headers HashMap property.