How to read erlang tuple saved in mongodb with java

Question

            A= term_to_binary({100,200,123,45}) ,
            io:format("~p~n",[A]),
            mongo:save(?IP_ADDRESS, {'_id', 1, ip,A}).

the result is <<131,104,4,97,100,97,200,97,123,97,45>>

and I need to read it in java

    DBObject a = IpTable.findOne(new BasicDBObject("_id",1));
    byte[] t=null;
    try
    {
        String u = a.get("ip").toString();
        System.out.println(u);
            t= u.getBytes("ISO8859-1");
    }
    catch(Exception ex)
    {

    }
    for(int i=0;i<t.length;i++)
    System.out.print(t[i]+",");
    System.out.println();

the result is

63,104,4,97,100,98,0,0,7,63,97,123,97,45,

if I change the first bytes into 131

    t[0]=(byte)131;
    try
    {
        OtpInputStream ois = null;
        ois = new OtpInputStream(t);
        OtpErlangTuple IP = (OtpErlangTuple)OtpErlangObject.decode(ois);
        System.out.println(IP);}

the result is {100,63,123,45} is wrong

its probably an encoding issue when you `toString()` the object or `getBytes()` the data. Check out http://stackoverflow.com/questions/16909645/how-to-read-erlang-term-from-redis-by-using-java-client/19369461#19369461 — Daniel, Dec 20 '13 at 16:15

score 0 · Answer 1 · answered Dec 18 '13 at 08:37

By specifying term_to_binary, you are trying to convert erlang term to binary. The same should be converted using binary_to_term to get back the result. Storing thing information in mongodb and you are trying to do a different conversion here.

Hence you result is wrong

1> A= term_to_binary({100,200,123,45}).
<<131,104,4,97,100,97,200,97,123,97,45>>
2> binary_to_term(A).
{100,200,123,45}

and

String u = a.get("ip").toString();

in short "{a,b,c,d}" in java is not same as term_to_binary({a,b,c,d}) of erlang

here you are converting the binary erlang term to string. if you want to save you have to save to string and then binary and then retrieve it.

How to read erlang tuple saved in mongodb with java

1 Answers1