Question

My Java program will be receiving messages with a predefined structure. Each message has multiple fields, and the next field may have certain values (and should be processed in certain way) depending on the current field value:

For example:

 1. FIELD1-FIELD2-CUSTOMDATA-OTHERDATA
 2. FIELD1-FIELD2-FIELD3-CUSTOMDATA-OTHERDATA

Here, depending on the type of FIELD1, certain decoding logic should run next; So certain parser should be used.

Is there any design pattern for such ?

I have thought of defining a class for each message type and provide the input step by step to certain implementation. But this doesn’t sound too good for me.

Thoughts?

Thanks in advance.

Answer 1

Unless you need the structure to be changed dynamically, I would write a parser which uses a switch and listener to handle the messages.

interface MessageListener {
    void message1(String field2, Object customData, Object otherData);
    void message2(String field2, String field3, Object customData, Object otherData);
    // other message types
}


MessageListener ml = 
String firstField = getField();
switch(firstField) {
    case messageType1: {
        String field2 = getField();
        Object customData = getData();
        Object otherData = getData();
        ml.message1(field2, customData, otherData);
        break;
    }
    case messageType2: {
        String field2 = getField();
        String field3 = getField();
        Object customData = getData();
        Object otherData = getData();
        ml.message2(field2, field3, customData, otherData);
        break;
    }
    //parse other message types

    default:
        // report unknown message type.
}