我有一个Java程序，可以将一些文本输出到控制台。它使用print，println和其他一些方法来执行此操作。
在程序结束时，我想读取控制台中的所有文本并将其复制到String缓冲区中。我怎么能用Java做到这一点？我需要单独阅读stdout和stderr。
答案 0 :(得分：18)
好的，这是一个有趣的问题。似乎并不是一种优雅的方法，可以同时为所有PrintStream方法解决它。 （不幸的是没有FilterPrintStream。）
我确实编写了一个丑陋的基于反射的解决方法（不要在生产代码中使用我想：）
class LoggedPrintStream extends PrintStream {
final StringBuilder buf;
final PrintStream underlying;
LoggedPrintStream(StringBuilder sb, OutputStream os, PrintStream ul) {
super(os);
this.buf = sb;
this.underlying = ul;
}
public static LoggedPrintStream create(PrintStream toLog) {
try {
final StringBuilder sb = new StringBuilder();
Field f = FilterOutputStream.class.getDeclaredField("out");
f.setAccessible(true);
OutputStream psout = (OutputStream) f.get(toLog);
return new LoggedPrintStream(sb, new FilterOutputStream(psout) {
public void write(int b) throws IOException {
super.write(b);
sb.append((char) b);
}
}, toLog);
} catch (NoSuchFieldException shouldNotHappen) {
} catch (IllegalArgumentException shouldNotHappen) {
} catch (IllegalAccessException shouldNotHappen) {
}
return null;
}
}
......可以像这样使用：
public class Test {
public static void main(String[] args) {
// Create logged PrintStreams
LoggedPrintStream lpsOut = LoggedPrintStream.create(System.out);
LoggedPrintStream lpsErr = LoggedPrintStream.create(System.err);
// Set them to stdout / stderr
System.setOut(lpsOut);
System.setErr(lpsErr);
// Print some stuff
System.out.print("hello ");
System.out.println(5);
System.out.flush();
System.err.println("Some error");
System.err.flush();
// Restore System.out / System.err
System.setOut(lpsOut.underlying);
System.setErr(lpsErr.underlying);
// Print the logged output
System.out.println("----- Log for System.out: -----\n" + lpsOut.buf);
System.out.println("----- Log for System.err: -----\n" + lpsErr.buf);
}
}
结果输出：
hello 5
Some error
----- Log for System.out: -----
hello 5
----- Log for System.err: -----
Some error
（但请注意，out中的FilterOutputStream字段受到保护并记录在案，因此它是API的一部分： - ）
答案 1 :(得分：5)
程序运行完毕后，您无法执行此操作。您需要在程序开始写输出之前执行此操作。
有关如何替换stdout和stderr的详细信息，请参阅this article。核心电话是System.setOut()和System.setErr()。
答案 2 :(得分：1)
您可以使用PipedInputStream和PipedOutputStream。
//create pairs of Piped input and output streasm for std out and std err
final PipedInputStream outPipedInputStream = new PipedInputStream();
final PrintStream outPrintStream = new PrintStream(new PipedOutputStream(
outPipedInputStream));
final BufferedReader outReader = new BufferedReader(
new InputStreamReader(outPipedInputStream));
final PipedInputStream errPipedInputStream = new PipedInputStream();
final PrintStream errPrintStream = new PrintStream(new PipedOutputStream(
errPipedInputStream));
final BufferedReader errReader = new BufferedReader(
new InputStreamReader(errPipedInputStream));
final PrintStream originalOutStream = System.out;
final PrintStream originalErrStream = System.err;
final Thread writingThread = new Thread(new Runnable() {
@Override
public void run() {
try {
System.setOut(outPrintStream);
System.setErr(errPrintStream);
// You could also set the System.in here using a
// PipedInputStream
DoSomething();
// Even better would be to refactor DoSomething to accept
// PrintStream objects as parameters to replace all uses of
// System.out and System.err. DoSomething could also have
// an overload with DoSomething() calling:
DoSomething(outPrintStream, errPrintStream);
} finally {
// may also want to add a catch for exceptions but it is
// essential to restore the original System output and error
// streams since it can be very confusing to not be able to
// find System.out output on your console
System.setOut(originalOutStream);
System.setErr(originalErrStream);
//You must close the streams which will auto flush them
outPrintStream.close();
errPrintStream.close();
}
} // end run()
}); // end writing thread
//Start the code that will write into streams
writingThread.start();
String line;
final List<String> completeOutputStreamContent = new ArrayList<String>();
while ((line = outReader.readLine()) != null) {
completeOutputStreamContent.add(line);
} // end reading output stream
final List<String> completeErrorStreamContent = new ArrayList<String>();
while ((line = errReader.readLine()) != null) {
completeErrorStreamContent.add(line);
} // end reading output stream
答案 3 :(得分：1)
这是一个名为ConsoleOutputCapturer的实用程序类。它允许输出转到现有控制台，但是在场景后面继续捕获输出文本。您可以使用start / stop方法控制要捕获的内容。换句话说，调用start开始捕获控制台输出，一旦完成捕获，就可以调用stop方法，该方法返回一个String值，该值保存控制台输出，用于启动 - 停止调用之间的时间窗口。这个类虽然不是线程安全的。
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.io.PrintStream;
import java.util.Arrays;
import java.util.List;
public class ConsoleOutputCapturer {
private ByteArrayOutputStream baos;
private PrintStream previous;
private boolean capturing;
public void start() {
if (capturing) {
return;
}
capturing = true;
previous = System.out;
baos = new ByteArrayOutputStream();
OutputStream outputStreamCombiner =
new OutputStreamCombiner(Arrays.asList(previous, baos));
PrintStream custom = new PrintStream(outputStreamCombiner);
System.setOut(custom);
}
public String stop() {
if (!capturing) {
return "";
}
System.setOut(previous);
String capturedValue = baos.toString();
baos = null;
previous = null;
capturing = false;
return capturedValue;
}
private static class OutputStreamCombiner extends OutputStream {
private List<OutputStream> outputStreams;
public OutputStreamCombiner(List<OutputStream> outputStreams) {
this.outputStreams = outputStreams;
}
public void write(int b) throws IOException {
for (OutputStream os : outputStreams) {
os.write(b);
}
}
public void flush() throws IOException {
for (OutputStream os : outputStreams) {
os.flush();
}
}
public void close() throws IOException {
for (OutputStream os : outputStreams) {
os.close();
}
}
}
}
答案 4 :(得分：0)
之后不要这样做，在调用第一个StringBuilder之前创建两个System.out.print()对象，然后将要保存的每个字符串追加到相应的StringBuilder。
答案 5 :(得分：0)
这两行代码会将您的输出放在一个文本文件中，或者您可以根据需要更改目标。
//创建一个文件： System.setOut（new PrintStream（new FileOutputStream（“D：/MyOutputFile.txt”）））; //将输出重定向到文件： System.out.println（“Hello to custom output stream！”）;
希望对你有所帮助..：）