Zookeeper的RPC框架

org.apache.zookeeper.ClientCnxn.java

该类管理客户端到HBase集群的socket I/O

所有需要通过socket发送的消息全部打包成Packet对象，然后放到ClentCnxn的outgoingQueue（LinkedList<Packet>）中，对outgoingQueue的操作需要同步控制。需要接受的消息也会被打包成Packet对象，放入pendingQueue（LinkedList<Packet>）中，等待一个答复。下面介绍一下设计的其他类及各类的使用方法及处理逻辑。

(一)Packet.java

 

static class Packet {
        RequestHeader header;

        ByteBuffer bb;

        /** Client's view of the path (may differ due to chroot) **/
        String clientPath;
        /** Servers's view of the path (may differ due to chroot) **/
        String serverPath;

        ReplyHeader replyHeader;

        Record request;

        Record response;

        boolean finished;

        AsyncCallback cb;

        Object ctx;

        WatchRegistration watchRegistration;

        Packet(RequestHeader header, ReplyHeader replyHeader, Record record,
                Record response, ByteBuffer bb,
                WatchRegistration watchRegistration) {
            this.header = header;
            this.replyHeader = replyHeader;
            this.request = record;
            this.response = response;
            if (bb != null) {
                this.bb = bb;
            } else {
                try {
                    ByteArrayOutputStream baos = new ByteArrayOutputStream();
                    BinaryOutputArchive boa = BinaryOutputArchive
                            .getArchive(baos);
                    boa.writeInt(-1, "len"); // We'll fill this in later
                    header.serialize(boa, "header");
                    if (record != null) {
                        record.serialize(boa, "request");
                    }
                    baos.close();
                    this.bb = ByteBuffer.wrap(baos.toByteArray());
                    this.bb.putInt(this.bb.capacity() - 4);
                    this.bb.rewind();
                } catch (IOException e) {
                    LOG.warn("Ignoring unexpected exception", e);
                }
            }
            this.watchRegistration = watchRegistration;
        }

        @Override
        public String toString() {
            StringBuilder sb = new StringBuilder();

            sb.append("clientPath:" + clientPath);
            sb.append(" serverPath:" + serverPath);
            sb.append(" finished:" + finished);

            sb.append(" header:: " + header);
            sb.append(" replyHeader:: " + replyHeader);
            sb.append(" request:: " + request);
            sb.append(" response:: " + response);

            // jute toString is horrible, remove unnecessary newlines
            return sb.toString().replaceAll("\r*\n+", " ");
        }
    }

 

　　

 

 该类含多个成员变量，主要的逻辑集中在构造函数中，若传入的字节数组（bb）内容非空，就将输入的"请求头（RequestHeader）"和“请求内容”（如：ExistRequest）转换成字节数组放入ByteBuffer中。其toString（）方法将所有的字段输出，并最后替换掉回车与换行之间的部分成空格。

1)RequestHeader.java

 

在RequestHeader中有两个整型变量，Xid和type，type标志着操作类型，如：ping，auth，详见OpCode接口中的静态常量。

 

Xid是一个操作序号，针对非ping和auth的操作，对于特定的ClientCnxn每次都会将该序号加1，然后传递给RequestHeader。

2)ReplyHeader extends record

 在PendingQueue接收返回数据，

3)Request extends record

记录请求内容

4)Response extends record

 记录回应内容