Логирование в Java с System.err

Этот способ подходит разве что для лабораторных работ, но не для реальных приложений:

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;

public class SystemErrMainClass {

    public static void main(String[] args) {
        System.out.println("My application started");
        try {
            Files.readAllBytes(Paths.get("/file/does/not/exist"));
        } catch (IOException ioex) {
            System.err.println("Failed to read file.");
            ioex.printStackTrace();
        }
    }

}

import java.io.IOException;

import java.nio.file.Files;

import java.nio.file.Paths;

public class SystemErrMainClass {

public static void main(String[] args) {

System.out.println("My application started");

try {

Files.readAllBytes(Paths.get("/file/does/not/exist"));

} catch (IOException ioex) {

System.err.println("Failed to read file.");

ioex.printStackTrace();

}

Как видите, мы просто используем System.out и System.err для логирования. Эта статья здесь просто так, для примера. Не нужно исползовать такой подход в реальных приложениях.

Если вы запустите код выше, то результат будет таким:

My application started
Failed to read file.
java.nio.file.NoSuchFileException: \file\does\not\exist
        at java.base/sun.nio.fs.WindowsException.translateToIOException(WindowsException.java:85)
        at java.base/sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:103)
        at java.base/sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:108)
        at java.base/sun.nio.fs.WindowsFileSystemProvider.newByteChannel(WindowsFileSystemProvider.java:235)
        at java.base/java.nio.file.Files.newByteChannel(Files.java:373)
        at java.base/java.nio.file.Files.newByteChannel(Files.java:424)
        at java.base/java.nio.file.Files.readAllBytes(Files.java:3280)
        at SystemErrMainClass.main(SystemErrMainClass.java:10)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
        at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.base/java.lang.reflect.Method.invoke(Method.java:567)
        at jdk.compiler/com.sun.tools.javac.launcher.Main.execute(Main.java:415)
        at jdk.compiler/com.sun.tools.javac.launcher.Main.run(Main.java:192)
        at jdk.compiler/com.sun.tools.javac.launcher.Main.main(Main.java:132)

My application started

Failed to read file.

java.nio.file.NoSuchFileException: \file\does\not\exist

at java.base/sun.nio.fs.WindowsException.translateToIOException(WindowsException.java:85)

at java.base/sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:103)

at java.base/sun.nio.fs.WindowsException.rethrowAsIOException(WindowsException.java:108)

at java.base/sun.nio.fs.WindowsFileSystemProvider.newByteChannel(WindowsFileSystemProvider.java:235)

at java.base/java.nio.file.Files.newByteChannel(Files.java:373)

at java.base/java.nio.file.Files.newByteChannel(Files.java:424)

at java.base/java.nio.file.Files.readAllBytes(Files.java:3280)

at SystemErrMainClass.main(SystemErrMainClass.java:10)

at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)

at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

at java.base/java.lang.reflect.Method.invoke(Method.java:567)

at jdk.compiler/com.sun.tools.javac.launcher.Main.execute(Main.java:415)

at jdk.compiler/com.sun.tools.javac.launcher.Main.run(Main.java:192)

at jdk.compiler/com.sun.tools.javac.launcher.Main.main(Main.java:132)

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