Erlang 聊天室程序(三) 数据交换格式json的decode

霸哥的blog中提到过Erlang服务器在通信中与客户端的数据交换方式：yufeng

为了简单起见这个聊天室程序采用json，要使用到rfc4627这个库

先定义一个Message类：

public class Message {
	String id;   //消息ID
	String type; //消息类型
	String from; //发送方
	String to;   //接收方
	String subject; //主题
	String content; //内容
	Date   creationDate; //时间
	
	public Message(String type,String from,String to,String subject,String content){
		this.id =MessageIdGenerator.nextId();
		this.type=type;
		this.from=from;
		this.to=to;
		this.subject=subject;
		this.content=content;
		this.creationDate=new Date();
	}

	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getType() {
		return type;
	}

	public void setType(String type) {
		this.type = type;
	}

	public String getFrom() {
		return from;
	}

	public void setFrom(String from) {
		this.from = from;
	}

	public String getTo() {
		return to;
	}

	public void setTo(String to) {
		this.to = to;
	}

	public String getSubject() {
		return subject;
	}

	public void setSubject(String subject) {
		this.subject = subject;
	}

	public String getContent() {
		return content;
	}

	public void setContent(String content) {
		this.content = content;
	}

	public Date getCreationDate() {
		return creationDate;
	}

	public void setCreationDate(Date creationDate) {
		this.creationDate = creationDate;
	}					
}

再定义一个JSON的工具类：

public class JSONParaser {	
	public static JSONObject getJSON(Object content){		
		try{
			JSONObject result = JSONObject.fromObject(content);					
			return result;
		}
		catch(Exception ex){
			return null;
		}		
	}
	
	public static Object getString(String json){
		try{
			JSONObject jobj=JSONObject.fromObject(json);		
			return JSONObject.toBean(jobj);
		}
		catch(Exception ex){
			return null;
		}	
	}	
}

再修改SOCKET 发送部分代码：

	public void sendMsg(Message msg){
		try {					
			String data=(JSONParaser.getJSON(msg)).toString();
			oust.write(data.getBytes());
			oust.flush();
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

测试下发送后服务器端接收到的数据：

client_session dwmsg recived {message,undefined,msg,
                                      [6],
                                      undefined,undefined,
                                      <<"{\"content\":\"aaaaa\",\"creationDate\":{\"date\":27,\"day\":1,\"hours\":13,\"minutes\":10,\"month\":1,\"seconds\":26,\"time\":1330319426281,\"timezoneOffset\":-480,\"year\":112},\"from\":\"client1\",\"id\":\"x8yL-2\",\"subject\":\"chat\",\"to\":\"\",\"type\":\"msg\"}">>,
                                      undefined}
client_session dwmsg sended

服务器端新建一个模块util_MessageParas，将收到的json数据转成内部可识的message：

%% Author: Administrator
%% Created: 2012-2-27
%% Description: TODO: Add description to util_MessageParas
-module(util_MessageParas).

%%
%% Include files
%%
%%-include("json.hrl").
-include("message.hrl").
%%
%% Exported Functions
%%<<"{\"content\":\"aaa\",\"creationDate\":{\"date\":27,\"day\":1,\"hours\":18,\"minutes\":8,\"month\":1,\"seconds\":26,\"time\":1330337306984,\"timezoneOffset\":-480,\"year\":112},\"from\":\"client1\",\"id\":\"289n-2\",\"subject\":\"chat\",\"to\":\"\",\"type\":\"msg\"}">>
-export([paraseDecode/1]).

%%
%% API Functions
%%



%%
%% Local Functions
%%
%paras json data to message
paraseDecode(Bin)->
	case rfc4627:decode(Bin) of
		{ok,Obj,_Re}->
			paraElements(Obj);
		{error,Reason}->
			{error,Reason}
	end
.

%we get elements from decoded json,
%it has to be 7 elements

paraElements(Obj)->
	{obj,List}=Obj,
	Data =#message{},
	%catch exception here
	try paraEle(List,Data)		
	catch
		{error,Reason,NewData}->
			io:format("Format"),
			{error,Reason,NewData}
	end
.

paraEle([Ele|Els],Data)->
	NewData=para(Ele,Data),
	paraEle(Els,NewData)
;
paraEle([],Data)->
	Data
.

%length of content should not more than 1000
para({"content",Val},Data) when is_binary(Val)->
	io:format("para content:~p~n",[Data]),
	Content=binary_to_list(Val),
	if length(Content)<1000 ->
			   NewData=Data#message{content=Content},
			   io:format("paraed content:~p~n",[NewData]),
			   NewData;
	   true ->			   
               throw({error,"illegal Content value",Data})				
	end
;
para({"to",Val},Data) when is_binary(Val)->
	io:format("para to:~p~n",[Data]),
	To =binary_to_list(Val),
	NewData=Data#message{to=To}
;
para({"id",Val},Data) when is_binary(Val)->
	io:format("para id:~p~n",[Data]),
	Id=binary_to_list(Val),
	NewData=Data#message{id=Id}
;
para({"subject",Val},Data) when is_binary(Val)->
	io:format("para subject:~p~n",[Data]),
	Sub=binary_to_list(Val),
	%we should validate subject here 
    if Sub=:="chat" ->
		   NewData=Data#message{subject=Sub};
	   true ->
		 %throw exception
		 throw({error,"illegal subject value",Data})
	end
;
para({"type",Val},Data) when is_binary(Val)->
	io:format("para type:~p~n",[Data]),
	Type = binary_to_list(Val),
	if Type=:="msg"->
		   NewData=Data#message{type=Type};
	   true ->
		 %throw exception
		 throw({error,"illegal type value",Data})
	end
;
para({"from",Val},Data) when is_binary(Val)->
	io:format("para from:~p~n",[Data]),
	From=binary_to_list(Val),
	NewData=Data#message{from=From}
;
para({"creationDate",Val},Data)->
	Data
;
para({Key,Val},Data)->
	%no mache
    %throw exception
	throw({error,"unkown element",Data})
.


paraseEncode()->
	ok
.

做下测试：

util_MessageParas:paraseDecode(<<"{\"content\":\"aaa\",\"creationDate\":{\"date\":27,\"day\":1,\"hours\":18,\"minutes\":8,\"month\":1,\"seconds\":26,\"time\":1330337306984,\"timezoneOffset\":-480,\"year\":112},\"from\":\"client1\",\"id\":\"289n-2\",\"subject\":\"chat\",\"to\":\"\",\"type\":\"msg\"}">>).
para content:{message,undefined,undefined,undefined,undefined,undefined,
                      undefined,undefined}
paraed content:{message,undefined,undefined,undefined,undefined,undefined,
                        "aaa",undefined}
para from:{message,undefined,undefined,undefined,undefined,undefined,"aaa",
                   undefined}
para id:{message,undefined,undefined,"client1",undefined,undefined,"aaa",
                 undefined}
para subject:{message,"289n-2",undefined,"client1",undefined,undefined,"aaa",
                      undefined}
para to:{message,"289n-2",undefined,"client1",undefined,"chat","aaa",
                 undefined}
para type:{message,"289n-2",undefined,"client1",[],"chat","aaa",undefined}
{message,"289n-2","msg","client1",[],"chat","aaa",undefined}

OK，收到的数据可以正常地解析为message了。

注：

在此处只需要将json数据的外层转换为message消息。message消息针对不同的类型和作用会有不同的json内容，所以内层数据应该在具体的消息处理部分再调用相应的paras处理。