使用Runtime.exec时读取错误

Question

This question has been asked once before on Stack Overflow , but the stack trace is different than mine, and I don't think it is caused by the same thing.

This is my stack trace:

java.io.IOException: Read error
at java.io.FileInputStream.readBytes(Native Method)
at java.io.FileInputStream.read(Unknown Source)
at sun.nio.cs.StreamDecoder.readBytes(Unknown Source)
at sun.nio.cs.StreamDecoder.implRead(Unknown Source)
at sun.nio.cs.StreamDecoder.read(Unknown Source)
at java.io.InputStreamReader.read(Unknown Source)
at java.io.BufferedReader.fill(Unknown Source)
at java.io.BufferedReader.readLine(Unknown Source)
at java.io.BufferedReader.readLine(Unknown Source)
at General.App.cmdString(App.java:393)
at General.App.cpauString(App.java:422)
at Functionality.RegistryScanThread.USBDScan(RegistryScanThread.java:109)
at Functionality.RegistryScanThread.doInBackground(RegistryScanThread.java:51)
at Functionality.RegistryScanThread.doInBackground(RegistryScanThread.java:1)
at javax.swing.SwingWorker$1.call(Unknown Source)
at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at javax.swing.SwingWorker.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

This is a simplified version of the more complex program I wrote:

import java.util.*;
import java.io.*;
public class Test {

//global vars

public Test(){
    // initializeing stuffs
}
public static void main(String[] args){
    ArrayList<String> str = cmdString("reg query hklm");
    for(String s : str){
        System.out.println(s);
    }
}

public static ArrayList<String> cmdString(String command){
    boolean success = false;
    ArrayList<String> result = new ArrayList<String>();
    String line = "";
    try{ 
        Process p = Runtime.getRuntime().exec(command);
        BufferedReader input = new BufferedReader(new InputStreamReader(p.getInputStream()));
            while ((line = input.readLine()) != null) {result.add(new String(line));}
        BufferedReader input2 = new BufferedReader(new InputStreamReader(p.getErrorStream()));
            while ((line = input2.readLine()) != null) {result.add(new String(line));}
        int exitvalue = p.waitFor();
        if (exitvalue != 0){
            System.out.println("error!!");
            success = false;

        }
        else{
            success = true;
        }
        for(String s : result){
            System.out.println(s);
        }
        input.close();
        input2.close();
        return result;
    } catch(Exception e) {
        e.printStackTrace(System.err);
        System.out.println("error!!!");
        return result;
    }
}
}

Basically. In the example above, the error isn't really visible. But in my program, it is executing everything correctly the first time I run it .

Then... when I run it a second or third time, an error occurs. Also... it seems that when I wait for a while before running it again, no error seems to occur.

How would I solve this issue?

Answer 1

This is what I think the answer is, and I'm sorry that it would have been impossible to answer my question based only on the code I gave.

Basically what happened was this.

1. My cmdString() method in my program was initiating a process and trying to read from its output stream and its error stream.
2. It so happens that the Process that my program was initiated, was a C++ application designed by me which used custom pipes to redirect input and output.
3. This C++ application had a pipe for standard output, but I happened to not make one for standard error.
4. Because I did not create a standard error pipe, my cmdString() method was trying to read from a pipe that I didn't create. So therefore I got the error on the line "line = input2.readLine())" which corresponded to the error stream.
5. So in summary, the error was due to trying to read an Error Stream from a process that did not produce an error stream.

I believe this is what happened.

I discovered the error when I saw the exact line that triggered the error. I was able to see that the normal stream did not produce the error, but the error stream did. I thought this was weird, and I instantly remembered that my C++ application did not have an error stream.

Let me know if this answer makes sense!