java - 超出 BufferedReader 的大小限制？

Question

在 java 6 web 应用程序中，我尝试从执行的命令中检索大量输出。我在 javaworld article 上“借用/窃取/基于”它。我面临的问题是，由于输出被截断，长度似乎超出了大小限制。我已将数据输出到文件中，以便可以看到返回的大小，这正是 32K (32768)。我尝试过更改缓冲区的默认大小(请参阅 BufferedReader 构造函数)，但无论我的缓冲大小值(非常小到非常大)，我都没有观察到返回数据的长度有任何变化.

如有任何建议，我们将不胜感激!

public class StreamGobbler extends Thread {

private InputStream is;
private String type;
private List<String> output;

public StreamGobbler(InputStream is, String type) {
    this.is = is;
    this.type = type;
}

@Override
public void run() {
    try {
        InputStreamReader isr = new InputStreamReader(is);
        BufferedReader br = new BufferedReader(isr);
        String line = null;
        this.output = new ArrayList<String>();
        while ((line = br.readLine()) != null) {
            this.getOutput().add(line + "\n");
            System.out.println(type + ">" + line);
        }
        br.close();
    } catch (IOException ioe) {
        System.err.println("ERROR: " + ioe.getMessage());
    }
}

/**
 * @return the output
 */
public List<String> getOutput() {
    return output;
}

}

public class JobClassAds {

private String CONDOR_HISTORY = "condor_history";
private String CONDOR_HISTORY_XML = CONDOR_HISTORY + " -xml";
private String CONDOR_HISTORY_LONG = CONDOR_HISTORY + " -long";

public String getHistory() {
    try {
        Runtime runtime = Runtime.getRuntime();
        String exec = CONDOR_HISTORY_LONG;
        Process process = runtime.exec(exec);
        System.out.println("Running " + exec + " ...");

        // Error message
        StreamGobbler errGobbler = new StreamGobbler(process.getErrorStream(), "ERROR");

        // Output
        StreamGobbler outGobbler = new StreamGobbler(process.getInputStream(), "OUTPUT");

        Thread outThread = new Thread(outGobbler);
        Thread errThread = new Thread(errGobbler);

        outThread.start();
        errThread.start();

        outThread.join();
        errThread.join();

        /*
        String line = null;

        while ((line = input.readLine()) != null) {
            System.out.println(line);
            content.append(line);
        }

         *
         */

        int exitVal = process.waitFor();

        List<String> output = outGobbler.getOutput();
        String inputString = "";
        for (String o : output) {
            inputString += o;
        }

        System.out.println(exec + " Exited with error code " + exitVal);

        BufferedWriter out = new BufferedWriter(new FileWriter("/tmp/history_result.xml"));
        out.write(inputString);
        out.close();
        return inputString;

    } catch (Exception e) {
        System.err.println(e.getMessage());
        return null;
    }
}

Answer 1

问题不在于 BufferedReader 的缓冲区大小。

我认为真正的原因是外部命令正在执行的操作。我怀疑它是在没有刷新其标准输出流的情况下退出的。请注意，您正在“吞噬”但没有输出命令的 stderr 流。您可以在那里找到指向问题真正原因的证据。

<小时/>

顺便说一句，您正在以次优的方式使用 StreamGobbler 类。它扩展了Thread，因此预期的使用方式是:

    SteamGobbler sg = new StreamGobbler(...);
    sg.start();
    sg.join();

但你实际上正在这样做:

    SteamGobbler sg = new StreamGobbler(...);
    Thread th = new Thread(sg);
    th.start();
    th.join();

它可以工作......但只是因为线程是一个可运行。