Accessing program messages output to error stream

I've created a class which processes files and if it encounters certain specific errors, it outputs relevant error messages to the error stream.

I am working on another class that needs to access these error messages. I'm not sure how to do this. I am a beginner in Java programming. Based on my limited knowledge, I thought that my two options would be to either call the main method of the first class (but I don't know how I would get the error messages in this case) or to execute the compiled class and access the messages through the getErrorStream() method of the Process class. But, I am having trouble with the system deadlocking or possibly not even executing the exec command, so I'm not sure how implement t开发者_JAVA百科he second case either.

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I'm not quite sure what you're asking here, but a potential problem with your code is that you're not reading from the process' stdout. Per the Process API, "failure to promptly ... read the output stream of the subprocess may cause the subprocess to block, and even deadlock." Is this the "trouble" you mentioned?

Edit: So yeah, you can either do what you're doing, but be sure to read both the error stream and the output stream (see my comment), or you could just call the main method directly from your code, in which case the error output will be written to System.err. You could use System.setErr() to install your own stream that would let you get what's written to it, but keep in mind that any error output from your own app--the one that's running the other app--will also show up here. It sounds like spawning a separate process, like you're already doing, is what you want.

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You can't build modularity based on many little programs with a main method. You have to make blocks of function as classes that are designed to be called from elsewhere -- and that means returning status information in some programmatic fashion, not just blatting it onto System.err. If it really is an error, throw an exception. If you have to return status, design a data structure to hold the status and return it. But don't go launching new processes all over the place and reading their error streams.