ProtoType 消息体创建

消息实体：

MsgLite.MsgLiteInner msg = MsgLite.MsgLiteInner.newBuilder()
                .setProtoType(20)
                .setProtoClientNo(1)
                .build();

        UserAuth.UserAuthInner userAuthInner = UserAuth.UserAuthInner.newBuilder()
                .setAuthType(1)
                .setAppId(appId)
                .setUserName(userName)
                .setPwd("")
                .setTimestamp(timeStamp)
                .setDevice(20)
                .setSig(sign)
                .setSdkVersion("5.4.2r")
                .setImei("00:FF:76:0F:C4:7B")
                .setMode(1)
                .setNetwork(5)
                .build();

        MsgLite.MsgLiteInner msgLite = ImMessageBuilder.builder()
                .setContainer(msg)
                .setBody(userAuthInner)
                .build();

创建消息代码如下

com.yuntongxun.client.ImMessageBuilder

@Slf4j
public class ImMessageBuilder {

    private MsgLite.MsgLiteInner msgLiteInner;

    private byte[] payload;

    public static ImMessageBuilder builder() {
        return new ImMessageBuilder();
    }

    public ImMessageBuilder setContainer(MsgLite.MsgLiteInner msgLite) {
        this.msgLiteInner = msgLite;
        return this;
    }

    public <T extends MessageLite> ImMessageBuilder setBody(T t) {
        // 作为输出流接收数据
        ByteArrayOutputStream byteArrayOut = new ByteArrayOutputStream();
        try {
            // 包装
            CodedOutputStream codedOut = CodedOutputStream.newInstance(byteArrayOut);
            codedOut.writeUInt32NoTag(t.getSerializedSize());
            t.writeTo(codedOut);
            // 不管当前缓冲区是否已满，强迫操作系统把缓冲区的内容立刻发送出去
            codedOut.flush();
            // 把输出流的值赋值给payload 
            this.payload = byteArrayOut.toByteArray();
        } catch (Exception e) {
            log.warn("设置请求内容失败", e);
        } finally {
            try {
                byteArrayOut.close();
            } catch (Exception e) {
            }
        }
        return this;
    }
    
    // 通过给msgLiteInner赋值返回一个MsgLite.MsgLiteInner 类型
    public MsgLite.MsgLiteInner build() {
        if(this.payload!=null){
            return msgLiteInner.toBuilder().setProtoData(ByteString.copyFrom(this.payload)).build();
        }
        return msgLiteInner.toBuilder().build();
    }
}

分析
msg 标识此次传输消息的protoType，setBody() 存入消息实体，ByteArrayOutputStream可以在内存中模拟一个OutputStream，实际上是把一个byte[]数组在内存中变成一个OutputStream，在写入完成之后强制发送出去。

关于writeUInt32NoTag() 用法详见
com.google.protobuf.CodedOutputStream.ArrayEncoder#writeUInt32NoTag以及博客​​protobuf序列化一个int型整数1​​