将数据写入java中调用的grep程序的InputStream

Question

我正在尝试处理从运行 diff 获得的数据到 java 程序中的 GNU grep 实例。我已经设法使用 Process 对象的 outputStream 获取 diff 的输出，但我目前正在让程序将此数据发送到 grep 的标准输入（通过用 Java 创建的另一个 Process 对象）。使用输入运行 Grep 仅返回状态代码 1。我做错了什么？

下面是我到目前为止的代码：

public class TestDiff {
final static String diffpath = "/usr/bin/";

public static void diffFiles(File leftFile, File rightFile) {

    Runtime runtime = Runtime.getRuntime();

    File tmp = File.createTempFile("dnc_uemo_", null);

    String leftPath = leftFile.getCanonicalPath();
    String rightPath = rightFile.getCanonicalPath();

    Process proc = runtime.exec(diffpath+"diff -n "+leftPath+" "+rightPath, null);
    InputStream inStream = proc.getInputStream();
    try {
        proc.waitFor();
    } catch (InterruptedException ex) {

    }

    byte[] buf = new byte[256];

    OutputStream tmpOutStream = new FileOutputStream(tmp);

    int numbytes = 0;
    while ((numbytes = inStream.read(buf, 0, 256)) != -1) {
        tmpOutStream.write(buf, 0, numbytes);
    }

    String tmps = new String(buf,"US-ASCII");

    inStream.close();
    tmpOutStream.close();

    FileInputStream tmpInputStream = new FileInputStream(tmp);

    Process addProc = runtime.exec(diffpath+"grep \"^a\" -", null);
    OutputStream addProcOutStream = addProc.getOutputStream();

    numbytes = 0;
    while ((numbytes = tmpInputStream.read(buf, 0, 256)) != -1) {
        addProcOutStream.write(buf, 0, numbytes);
        addProcOutStream.flush();
    }
    tmpInputStream.close();
    addProcOutStream.close();

    try {
        addProc.waitFor();
    } catch (InterruptedException ex) {

    }

    int exitcode = addProc.exitValue();
    System.out.println(exitcode);

    inStream = addProc.getInputStream();
    InputStreamReader sr = new InputStreamReader(inStream);
    BufferedReader br = new BufferedReader(sr);

    String line = null;
    int numInsertions = 0;
    while ((line = br.readLine()) != null) {

        String[] p = line.split(" ");
        numInsertions += Integer.parseInt(p[1]);

    }
    br.close();
}
}

leftPath 和 rightPath 都是指向要比较的文件的 File 对象。

Answer 1

只需几个提示，您可以：

• 将 diff 的输出直接通过管道传输到 grep 中： diff -n leftpath rightPath | grep "^a"
• 从 grep 而不是 stdin 读取输出文件： grep "^a" tmpFile
• 使用 ProcessBuilder 获取您的 Process ，您可以轻松避免阻塞过程，因为您没有使用 redirectErrorStream 读取 stderr