1-1-10-3 请问有谁知道如何将System.out重定向输出到一个JT
发信人: ttttt (如果), 信区: Java
标题: Re: 请问有谁知道如何将System.out重定向输出到一个JT
发信站: BBS 水木清华站 (Mon Oct 25 14:08:03 1999)
【 在 oldcrab(老蟹) 的大作中提到: 】
: 请问有谁知道如何将System.out重定向输出到一个JTextArea?
: 谢谢！
希望这个能帮你忙，呵呵
CAPTURING STANDARD OUTPUT IN A LOG FILE
This tip demonstrates how you can record in a log file everything you
print to standard out and standard error. This is especially useful
if you deploy an application and your users encounter problems. You
can have the users send you the log file for analysis.
The following example code demonstrates how to capture standard
output. You can include the example code, as is, in your program.
The example implements a class called SaveOutput, with two static
methods - start() and stop().Calling start() creates a new log
file or empties an existing log file. It copies into the log file
characters printed to standard output and standard error.Calling
stop() closes the log file and restores the behavior of standard
output and standard error (that is, their behavior before start() was
called).
import java.io.*;
class Stdout {
public static void main(String[] args) {
try {
// Start capturing characters into the log file.
SaveOutput.start("log.txt");
// Test it.
System.out.println("Here's is some stuff to stdout.");
System.err.println("Here's is some stuff to stderr.");
System.out.println("Let's throw an exception...");
new Exception().printStackTrace();
} catch (Exception e) {
e.printStackTrace();
} finally {
// Stop capturing characters into the log file
// and restore old setup.
SaveOutput.stop();
}
}
}
class SaveOutput extends PrintStream {
static OutputStream logfile;
static PrintStream oldStdout;
static PrintStream oldStderr;
SaveOutput(PrintStream ps) {
super(ps);
}
// Starts copying stdout and stderr to the file f.
public static void start(String f) throws IOException {
// Save old settings.
oldStdout = System.out;
oldStderr = System.err;
// Create/Open logfile.
logfile = new PrintStream(
new BufferedOutputStream(
new FileOutputStream(f)));
// Start redirecting the output.
System.setOut(new SaveOutput(System.out));
System.setErr(new SaveOutput(System.err));
}
// Restores the original settings.
public static void stop() {
System.setOut(oldStdout);
System.setErr(oldStderr);
try {
logfile.close();
} catch (Exception e) {
e.printStackTrace();
}
}
// PrintStream override.
public void write(int b) {
try {
logfile.write(b);
} catch (Exception e) {
e.printStackTrace();
setError();
}
super.write(b);
}
// PrintStream override.
public void write(byte buf[], int off, int len) {
try {
logfile.write(buf, off, len);
} catch (Exception e) {
e.printStackTrace();
setError();
}
super.write(buf, off, len);
}
}
The start() method first saves the current standard output and
standard error print streams.These print streams will be restored
when stop() is called. Next, the log file is opened.If the log
file does not exist, it's created.Otherwise, the log file is
emptied.Finally, System.setOut() and System.setErr() are called
to replace the standard output and standard error print streams with
SaveOutput print streams.
The stop () method restores the original standard output and
standard error. It then closes the log file.
A SaveOutput object is a PrintStream object that acts like a tee.
Any characters it receives are forwarded to two places: the log file
and the underlying print streams. The underlying print streams in
the example are the original standard output and standard error
print streams; these are supplied to the SaveOutput constructor.
Although both standard output and standard error are written into the
same logfile, there is no need to synchronize this operation.The
reason is that the logfile output stream is itself a print stream
and write operations are synchronized.
To implement this tee behavior, the program needs to override the
two forms of the write method. These overrides simply write the
characters into the logfile and then to the underlying print stream
(by calling super.write()). The write() methods do not throw
exceptions. Instead, they set a flag in the print stream if some
problem occurs. They set the flag by calling setError(). If the client
of the print stream wants to check if an error occurred, it can call
checkError().
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