MQTT的学习研究（八）基于HTTP DELETE MQTT 订阅消息服务端使用

HTTP DELETE 订阅主题请求协议和响应协议
http://publib.boulder.ibm.com/infocenter/wmqv7/v7r0/topic/com.ibm.mq.csqzau.doc/ts21240_.htm

请求响应头各个字段的含义的讲解
http://publib.boulder.ibm.com/infocenter/wmqv7/v7r0/topic/com.ibm.mq.csqzau.doc/ts21250_.htm

响应错误处理
http://publib.boulder.ibm.com/infocenter/wmqv7/v7r0/topic/com.ibm.mq.csqzau.doc/ts21340_.htm

The HTTP DELETE operation gets a message from a WebSphere® MQ queue, or retrieves a publication from a topic. The message is removed from the queue. If the publication is retained, it is not removed. A response message is sent back to the client including information about the message.

Syntax

Request

>>-+-DELETE-+-- --| Path |-- --HTTP version--CRLF--------------->
   '-GET----'                                       

   .-CRLF---------------.  .-CRLF---------------.   
   V                    |  V                    |   
>----+----------------+-+----+----------------+-+--------------->
     '-general-header-'      '-request-header-'     

   .-CRLF----------------------------.   
   V                                 |   
>----+-----------------------------+-+-------------------------><
     '-| Entity-header (Request) |-'     

Path

|--/--contextRoot--/-------------------------------------------->

>--msg/--+-queue/--queueName--+-------------+-+--/--------------|
         |                    '-@--qMgrName-' |      
         '-topic/--topicName------------------'      

entity-header (Request)

|--+----------------------------------------------+-------------|
   +-standard entity-header-- --entity-value------+   
   +-x-msg-correlId - --correlation ID------------+   
   +-x-msg-msgId - --message ID-------------------+   
   +-x-msg-range-- --range------------------------+   
   +-x-msg-require-headers-- --entity header name-+   
   '-x-msg-wait - --wait time---------------------'   

Note:

1. If a question mark (?) is used it must be substituted with %3f. For example, orange?topic should be specified as orange%3ftopic.
2. @qMgrName is only valid on an HTTP POST

Response

>>-HTTP version-- --HTTP Status-Code-- --HTTP Reason-Phrase--CRLF-->

   .-CRLF---------------.  .-CRLF----------------.   
   V                    |  V                     |   
>----+----------------+-+----+-----------------+-+-------------->
     '-general-header-'      '-response-header-'     

   .-CRLF-----------------------------.                      
   V                                  |                      
>----+------------------------------+-+--+---------------+-----><
     '-| Entity-header (Response) |-'    '-CRLF--Message-'   

entity-header (Response)

|--+-----------------------------------------+------------------|
   +-standard entity-header-- --entity-value-+   
   +-x-msg-class-- --message type------------+   
   +-x-msg-correlId-- --correlation ID-------+   
   +-x-msg-encoding-- --encoding type--------+   
   +-x-msg-expiry-- --duration---------------+   
   +-x-msg-format-- --message format---------+   
   +-x-msg-msgId-- --message ID--------------+   
   +-x-msg-persistence-- --persistence-------+   
   +-x-msg-priority-- --priority class-------+   
   +-x-msg-replyTo-- --reply-to queue--------+   
   +-x-msg-timestamp-- --HTTP-date-----------+   
   '-x-msg-usr-- --user properties-----------'   

Request parameters

PathSee URI Format.HTTP versionHTTP version; for example, HTTP/1.1general-headerSee HTTP/1.1 - 4.5 General Header Fields.request-headerSee HTTP/1.1 - 5.3 Request Header Fields. The Host field is mandatory on an HTTP/1.1 request. It is often automatically inserted by the tool you use to create a client request.entity-header (Request)See HTTP/1.1 - 7.1 Entity Header Fields. One of the entity headers listed in the Request syntax diagram.

Response parameters

PathSee URI Format.HTTP versionHTTP version; for example, HTTP/1.1general-headerSee HTTP/1.1 - 4.5 General Header Fields.response-headerSee HTTP/1.1 - 6.2 Response Header Fields.entity-header (Response)See HTTP/1.1 - 7.1 Entity Header Fields. One of the entity or response headers listed in the Response syntax diagram.The Content–Length is always present in a response. It is set to zero if there is no message body.MessageMessage body.

Description

If the HTTP DELETE request is successful, the response message contains the data retrieved from the WebSphere MQ queue. The number of bytes in the body of the message is returned in the HTTP Content-Length header. The status code for the HTTP response is set to 200 OK. If x-msg-range is specified as 0, or0-0, then the status code of the HTTP response is 204 No Content.

If the HTTP DELETE request is unsuccessful, the response includes a WebSphere MQ bridge for HTTP error message and an HTTP status code.

HTTP DELETE example

HTTP DELETE gets a message from a queue and deletes the message, or retrieves and deletes a publication. The HTTPDELETE Java sample is an example an HTTP DELETE request reading a message from a queue. Instead of using Java, you could create an HTTP DELETE request using a browser form, or an AJAX toolkit instead.

Figure 1 is an HTTP request to delete the next message on queue called myQueue. In response, the message body is returned to the client. In WebSphere MQ terms, HTTP DELETE is a destructive get.

The request contains the HTTP request header x-msg-wait, which instructs WebSphere MQ bridge for HTTP how long to wait for a message to arrive on the queue. The request also contains the x-msg-require-headersrequest header, which specifies that the client is to receive the message correlation ID in the response.

Figure 1. Example of an HTTP DELETE request

DELETE /msg/queue/myQueue/ HTTP/1.1
Host: www.example.org
x-msg-wait: 10
x-msg-require-headers: correlID

Figure 2, is the response returned to the client. The correlation ID is returned to the client, as requested in x-msg-require-headers of the request.

Figure 2. Example of an HTTP DELETE response

HTTP/1.1 200 OK
Date: Wed, 2 Jan 2007 22:38:34 GMT
Server: Apache-Coyote/1.1 WMQ-HTTP/1.1 JEE-Bridge/1.1
Content-Length: 50
Content-Type: text/plain; charset=utf-8
x-msg-correlId: 1234567890

Here's my message body that will appear on the queue.

HTTP DELETE订阅主题信息

package com.etrip.mqttv3.http;
/**
 * This sample shows how to delete a message. It has slightly enhanced function
 * of the amqsget command in that it will print out the timestamp, expiry and
 * persistence of the messages. The program continues until the queue is empty
 * or a request fails. This program can potentially take in three parameters:
 * <queueName>
 * <host:port> <context-root (the MQ Bridge for HTTP's context-root)>
 * defaults are: SYSTEM.DEFAULT.LOCAL.QUEUE localhost:8080 mq
 *
 * If there are any exceptions thrown from this program or errors returned from the server then they are
 * printed to standard output as-is.
 *
 * No more messages
 * HTTP DELETE Sample end
 */
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
/**
 *
 * 采用HTTP DELETE方式的订阅相关的MQTT的主题的信息
 *
 * @author longgangbai
 *
 *
 */
public class HTTPDELETE
{
   private static final String DEFAULT_HOST = "localhost";
   private static final String DEFAULT_PORT = "8080";
   private static final String DEFAULT_QUEUE = "SYSTEM.DEFAULT.LOCAL.QUEUE";

   private static final String DEFAULT_CONTEXT_ROOT = "mq";

   public static String newline = System.getProperty("line.separator");

   private static final String MESSAGE_BOUNDARY = "_________________________________________________________________________________________";

   // the maximum length of the message that we want to print to the screen
   private static final int MAX_OUTPUT_MESSAGE_SIZE = 256;


   private static int OK_RC = 200;


   /**
    * 构建订阅主题队列路径
    *
    * @param host
    * @param port
    * @param context
    * @param queueName
    */
    private static String getPublishQueueURL(String host, String port,
            String context, String queueName) {
        StringBuffer urlString =new StringBuffer("http://");
           if(StringUtils.isEmtry(host)){
               host=DEFAULT_HOST;
           }

           if(StringUtils.isEmtry(port)){
               port=DEFAULT_PORT;
           }
           urlString.append(host).append(":").append(port);
           if(StringUtils.isEmtry(context)){
               context=DEFAULT_CONTEXT_ROOT;
           }
           urlString.append("/");
           urlString.append(context);
           urlString.append("/msg/queue/");
           if(StringUtils.isEmtry(queueName)){
               queueName=DEFAULT_QUEUE;
           }
           urlString.append(queueName);
           System.out.println("urlString="+urlString);
           return urlString.toString();
    }


    /**
     *  通过HTTP POST 订阅主题的具体实现
     * @param host
     * @param port
     * @param context
     * @param queueName
     * @return
     * @throws MalformedURLException
     */
       public static boolean subTopic(String host,String port,String context,String queueName ){
              String publishURL=getPublishQueueURL(host, port, context, queueName);
              URL url=null;
              HttpURLConnection connection=null;
                try {
                      url = new URL(publishURL);
                      connection= (HttpURLConnection) url.openConnection();
                      /* Build the headers */
                      // the verb first.
                      connection.setRequestMethod("DELETE");

                      // write out what headers we want back
                      // the header names are case-sensitive
                      connection.setRequestProperty("x-msg-require-headers",
                            "timestamp, expiry, persistence");

                      // Now actually send the request message. There is no content as this is a
                      // DELETE
                      connection.connect();
                      String formattedMessage = null;
                      // check the response for errors
                      int responseCode = connection.getResponseCode();
                    if (responseCode == OK_RC)
                      {
                         // Get the headers first
                         String timestamp = connection.getHeaderField("x-msg-timestamp");
                         String expiry = connection.getHeaderField("x-msg-expiry");
                         String persistence = connection.getHeaderField("x-msg-persistence");
                         // now get the message data
                         BufferedReader reader = new BufferedReader(new InputStreamReader(
                               connection.getInputStream()));
                         String line = null;
                         StringBuffer messageBuffer = new StringBuffer();
                         while ((line = reader.readLine()) != null)
                         {
                            messageBuffer.append(line);
                         }
                         String messageBody = messageBuffer.toString();


                         formattedMessage = MESSAGE_BOUNDARY + newline;
                         // Which is greater the max output message size or the message length?
                         int messageSizeToPrint = messageBody.length() > MAX_OUTPUT_MESSAGE_SIZE ? MAX_OUTPUT_MESSAGE_SIZE
                               : messageBody.length();
                         formattedMessage += messageBody.substring(0, messageSizeToPrint)
                               + newline;
                         formattedMessage += "timestamp   = " + timestamp + newline;
                         formattedMessage += "expiry      = " + expiry + newline;
                         formattedMessage += "persistence = " + persistence + newline;

                         System.out.println("formattedMessage "+formattedMessage);
                      }else{
                          String responseMessage =connection.getResponseMessage();
                          System.out.println("responsere sponseCode "+responseCode+" response request ="+responseMessage);
                      }
                } catch (MalformedURLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }finally{
                    connection.disconnect();
                }
           return false;
       }

        public static void main(String[] args) {
           HTTPDELETE.subTopic("192.168.208.46", "8080", "mq", "java_lover");
        }

}