当客户端机器遇到网络问题时,我希望能运行一些命令并将它们的结果发送到我的电子邮件中。
我发现 Runtime.exec 可以让我执行任意命令,但是将结果收集到字符串中更加有趣。
我知道可以将输出重定向到文件,然后从文件中读取,但是我的直觉告诉我有一种更加优雅的方法。
您有什么建议吗?
StreamGobbler
机制,它可以在单独的线程中捕获stdout/err。这对于防止阻塞非常重要,如果不正确处理该机制,则会导致许多错误!使用ProcessBuilder。调用start()方法后,您将获得一个Process对象,从中可以获取stderr和stdout流。
更新:ProcessBuilder提供更多控制;您不必使用它,但我发现长期来看更容易。特别是能够将stderr重定向到stdout,这意味着您只需要下载一个流。
Commandline commandLine = new Commandline();
commandLine.setExecutable(executable.getAbsolutePath());
Collection<String> args = getArguments();
for (String arg : args) {
Arg _arg = commandLine.createArg();
_arg.setValue(arg);
}
WriterStreamConsumer systemOut = new WriterStreamConsumer(console);
WriterStreamConsumer systemErr = new WriterStreamConsumer(console);
returnCode = CommandLineUtils.executeCommandLine(commandLine, systemOut, systemErr, 10);
if (returnCode != 0) {
// bad
} else {
// good
}
对于不会生成大量输出的进程,我认为这个简单的解决方案可以使用Apache IOUtils:
Process p = Runtime.getRuntime().exec("script");
p.waitFor();
String output = IOUtils.toString(p.getInputStream());
String errorOutput = IOUtils.toString(p.getErrorStream());
这是我多年来一直在使用的帮助类。它只有一个小类,其中包含JavaWorld streamgobbler类以修复JVM资源泄漏问题。虽然不确定是否适用于JVM6和JVM7,但不会造成任何伤害。此帮助程序可以读取输出缓冲区以供稍后使用。
import java.io.*;
/**
* Execute external process and optionally read output buffer.
*/
public class ShellExec {
private int exitCode;
private boolean readOutput, readError;
private StreamGobbler errorGobbler, outputGobbler;
public ShellExec() {
this(false, false);
}
public ShellExec(boolean readOutput, boolean readError) {
this.readOutput = readOutput;
this.readError = readError;
}
/**
* Execute a command.
* @param command command ("c:/some/folder/script.bat" or "some/folder/script.sh")
* @param workdir working directory or NULL to use command folder
* @param wait wait for process to end
* @param args 0..n command line arguments
* @return process exit code
*/
public int execute(String command, String workdir, boolean wait, String...args) throws IOException {
String[] cmdArr;
if (args != null && args.length > 0) {
cmdArr = new String[1+args.length];
cmdArr[0] = command;
System.arraycopy(args, 0, cmdArr, 1, args.length);
} else {
cmdArr = new String[] { command };
}
ProcessBuilder pb = new ProcessBuilder(cmdArr);
File workingDir = (workdir==null ? new File(command).getParentFile() : new File(workdir) );
pb.directory(workingDir);
Process process = pb.start();
// Consume streams, older jvm's had a memory leak if streams were not read,
// some other jvm+OS combinations may block unless streams are consumed.
errorGobbler = new StreamGobbler(process.getErrorStream(), readError);
outputGobbler = new StreamGobbler(process.getInputStream(), readOutput);
errorGobbler.start();
outputGobbler.start();
exitCode = 0;
if (wait) {
try {
process.waitFor();
exitCode = process.exitValue();
} catch (InterruptedException ex) { }
}
return exitCode;
}
public int getExitCode() {
return exitCode;
}
public boolean isOutputCompleted() {
return (outputGobbler != null ? outputGobbler.isCompleted() : false);
}
public boolean isErrorCompleted() {
return (errorGobbler != null ? errorGobbler.isCompleted() : false);
}
public String getOutput() {
return (outputGobbler != null ? outputGobbler.getOutput() : null);
}
public String getError() {
return (errorGobbler != null ? errorGobbler.getOutput() : null);
}
//********************************************
//********************************************
/**
* StreamGobbler reads inputstream to "gobble" it.
* This is used by Executor class when running
* a commandline applications. Gobblers must read/purge
* INSTR and ERRSTR process streams.
* http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html?page=4
*/
private class StreamGobbler extends Thread {
private InputStream is;
private StringBuilder output;
private volatile boolean completed; // mark volatile to guarantee a thread safety
public StreamGobbler(InputStream is, boolean readStream) {
this.is = is;
this.output = (readStream ? new StringBuilder(256) : null);
}
public void run() {
completed = false;
try {
String NL = System.getProperty("line.separator", "\r\n");
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line;
while ( (line = br.readLine()) != null) {
if (output != null)
output.append(line + NL);
}
} catch (IOException ex) {
// ex.printStackTrace();
}
completed = true;
}
/**
* Get inputstream buffer or null if stream
* was not consumed.
* @return
*/
public String getOutput() {
return (output != null ? output.toString() : null);
}
/**
* Is input stream completed.
* @return
*/
public boolean isCompleted() {
return completed;
}
}
}
ShellExec exec = new ShellExec(true, false);
exec.execute("cscript.exe", null, true,
"//Nologo",
"//B", // batch mode, no prompts
"//T:320", // timeout seconds
"c:/my/script/test1.vbs", // unix path delim works for script.exe
"script arg 1",
"script arg 2",
);
System.out.println(exec.getOutput());
VerboseProcess
是来自jcabi-log的实用工具类,可以帮助您:
String output = new VerboseProcess(
new ProcessBuilder("executable with output")
).stdout();
只需要这个依赖:
<dependency>
<groupId>com.jcabi</groupId>
<artifactId>jcabi-log</artifactId>
<version>0.7.5</version>
</dependency>
Runtime.exec() 返回一个 Process 对象,你可以从中提取你运行的任何命令的输出。