[七]RabbitMQ-客户端源码之AMQPImpl+Method

AMQPImpl类包括AMQP接口（public class AMQImpl implements AMQP）主要囊括了AMQP协议中的通信帧的类别。

这里以Connection.Start帧做一个例子。

public static class Connection {
    public static final int INDEX = 10;

    public static class Start
        extends Method
        implements com.rabbitmq.client.AMQP.Connection.Start
    {
        public static final int INDEX = 10;

        private final int versionMajor;
        private final int versionMinor;
        private final Map<String,Object> serverProperties;
        private final LongString mechanisms;
        private final LongString locales;
....//下面省略很多代码。。。

可以看到Start类是Connection类的内部静态子类，表示此Start类为Connection.Start，而且Start类是继承Method方法的，包括接下来所有的AMQP协议帧都是继承这个Method方法，Method可以看成用来区分AMQP协议帧的类型。

Method类是一个抽象类(Base class for AMQP method objects, specialized by autogenerated code in AMQP.java)，我们来看下Method类的代码：

public abstract class Method implements com.rabbitmq.client.Method {
    /** {@inheritDoc} */
    public abstract int protocolClassId(); /* properly an unsigned short */

    /** {@inheritDoc} */
    public abstract int protocolMethodId(); /* properly an unsigned short */

    /** {@inheritDoc} */
    public abstract String protocolMethodName();

    /**
     * Tell if content is present.
     * @return true if the wire-protocol for this method should involve a content header and body,
     * or false if it should just involve a single method frame.
     */
    public abstract boolean hasContent();

    /**
     * Visitor support (double-dispatch mechanism).
     * @param visitor the visitor object
     * @return the result of the "visit" operation
     * @throws IOException if an error is encountered
     */
    public abstract Object visit(MethodVisitor visitor) throws IOException;

    /**
     * Private API - Autogenerated writer for this method.
     * @param writer interface to an object to write the method arguments
     * @throws IOException if an error is encountered
     */
    public abstract void writeArgumentsTo(MethodArgumentWriter writer) throws IOException;

    /**
     * Public API - debugging utility
     * @param buffer the buffer to append debug data to
     */
    public void appendArgumentDebugStringTo(StringBuilder buffer) {
        buffer.append("(?)");
    }

    @Override public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("#method<").append(protocolMethodName()).append(">");
        this.appendArgumentDebugStringTo(sb);
        return sb.toString();
    }

    public Frame toFrame(int channelNumber) throws IOException {
        Frame frame = new Frame(AMQP.FRAME_METHOD, channelNumber);
        DataOutputStream bodyOut = frame.getOutputStream();
        bodyOut.writeShort(protocolClassId());
        bodyOut.writeShort(protocolMethodId());
        MethodArgumentWriter argWriter = new MethodArgumentWriter(new ValueWriter(bodyOut));
        writeArgumentsTo(argWriter);
        argWriter.flush();
        return frame;
    }
}

代码不长。挑几个解释下。

protocolClassId()和protocolMethodId()：每一个Method（Connection.Start/.StartOk, Connection.Tune/.TuneOk等等）都包含classId和methodId,可以参考下图：

protocolMethodName()返回本Method的名称，比如Connection.Start的就是：

public String protocolMethodName() { return "connection.start";}

boolean hasContent()用来区分这个Method之后是否有Content-Body,比如Connection.Start的为：

public boolean hasContent() { return false; }

又比如Basic.Publish的为：

public boolean hasContent() { return true; }

下面是一张表，用来涵盖AQMP协议各个种类的Method以及其一些属性，看完这张表就看完了AMQPImpl的全部。

附：本系列全集

1. [Conclusion]RabbitMQ-客户端源码之总结
2. [一]RabbitMQ-客户端源码之ConnectionFactory
3. [二]RabbitMQ-客户端源码之AMQConnection
4. [三]RabbitMQ-客户端源码之ChannelManager
5. [四]RabbitMQ-客户端源码之Frame
6. [五]RabbitMQ-客户端源码之AMQChannel
7. [六]RabbitMQ-客户端源码之AMQCommand
8. [七]RabbitMQ-客户端源码之AMQPImpl+Method
9. [八]RabbitMQ-客户端源码之ChannelN
10. [九]RabbitMQ-客户端源码之Consumer