How can I find where the print called?

Question

I'm working on an old java application project using IntelliJ, the source code is huge. One class has a method which prints the info of video per frame while playing. I want to disable this code for printing but I have no idea where does it come from or what the class name is. It didn't show up when I searched the string directly. Is there a cleverer way to find where the print called?

(From comments):

Output line is [isDeveloper true]------ get duration(=3.552653) is test impl ------

Answer 1

Replace System.out with your own PrintStream , using System.setOut() , have it match the (un-)desired output, put a break-point on the match clause, and look at the stack trace.

---

Since PrintStream has many, many methods, instead of overwriting all of the possible methods that may be called when generating the (un-)desired output, let's direct all the PrintStream output to a FilterOutputStream of our own devising; then we should only have to overwrite one method, but we will need to reconstruct our string.

Example:

class Prospector extends FilterOutputStream {

    int count = 0;

    private OutputStream original;

    public Prospector(OutputStream out) {
        super(out);
        original = out;
    }

    @Override
    public void write(byte[] b, int off, int len) throws IOException {
        String buffer = new String(b, off, len, StandardCharsets.ISO_8859_1);
        if (buffer.contains("]------ get duration(=")) {
            if (count == 0) {
                new Exception().printStackTrace(original);
            }
            count++;  // Set breakpoint here
        }
        super.write(b, off, len);
    }
}

When the program starts, install a new PrintStream wrapping the original in our Prospector :

System.setOut(new PrintStream(new Prospector(System.out)));

Set a breakpoint on the indicated line. When the program stops at the breakpoint, look up the stack trace to find the class/method which generates the output.

When the mystery class generates your target line, which may be like ...

System.out.format("[%s %s]------ get duration(=%f) is %s -------%n",
    "isDeveloper", "true", 3.552653, "test impl");

... this method may be called multiple times, with buffer contain the individual parts of the line, in succession. In the above case, this would be:

• "["
• "isDeveloper"
• " "
• "true"
• "]------ get duration(="
• "3.552653"
• ") is "
• "test impl"
• " -------"
• "\\n"

Ideally, ]------ get duration(= should be unique enough to find the class/method you are looking for, but you can adapt as needed.

It is also possible that the entire text is formatted into a single String , and printed out in one call. This is why .contains(...) is used to match the required output.

Answer 2

i think

Pressing Ctrl+ Mouse click on required variable or method

acts as a hyperlink to source

should do the trick(on IntelliJ)