Chronicle Queue: How to read excepts/documents with different WireKey? - chronicle

Question

Assume a chronicle queue, and a producer that writes 2 types of messages into the queue.
Each type of message is written with a different "WireKey".
// Writes: {key1: TestMessage}
appender.writeDocument(w -> w.write("key1").text("TestMessage"));
// Writes: {key2: AnotherTextMessage}
appender.writeDocument(w -> w.write("key2").text("AnotherTextMessage"));
Question:
How can I write a single-threaded consumer that can read both types of messages and handle them differently?
What I've tried:
// This can read both types of messages, but cannot
// tell which type a message belongs to.
tailer.readDocument(wire -> {
wire.read().text();
});
// This only reads type "key1" messages, skips all "key2" messages.
tailer.readDocument(wire -> {
wire.read("key1").text();
});
// This crashes. (because it advances the read position illegally?)
tailer.readDocument(wire -> {
wire.read("key1").text();
wire.read("key2").text();
});
I was hoping I can do something like wire.readKey() and get the WireKey of a document, then proceed to read the document and handle it dynamically. How can I do this?
Note: I'm aware this can be accomplished using methodReader and methodWriter, and it seems like documentation/demo recommends this approach (?) But I'd prefer not to use that API, and be explicit about reading and writing messages. I assume there has to be a way to accomplish this use case.
Thank you.

Answer 1

You are correct, e.g. MethodReader accomplishes it.
You can do it two ways
// a reused StringBuilder
StringBuilder sb = new StringBuilder();
wire.read(sb); // populate the StringBuilder
or a more convenient method is
String name = wire.readEvent(String.class);
switch(name) {
case "key1":
String text1 = wire.getValueIn().text();
// do something with text1
break;
case "key2":
String text2 = wire.getValueIn().text();
// do something with text1
break;
default:
// log unexpected key
}
For other readers who don't know about MethodReader, the same messages can be accomplished with
interface MyEvents {
void key1(String text1);
void key2(String text2);
}
MyEvents me = wire.methodWriter(MyEvents.class);
me.key1("text1");
me.key2("text2");
MyEvents me2 = new MyEvents() {
public void key1(String text1) {
// handle text1
}
public void key2(String text2) {
// handle text2
}
};
Reader reader = wire.methodReader(me2;
do {
} while(reader.readeOne());
NOTE: The content is the same, so you can mix and match the two options
You can use a Chronicle Queue instead of a Wire to persist this information