How to Capture Output from External Programs Executed with Extra Parameters in Java?

Executing External Programs with Extra Parameters in Java

When attempting to execute an external program from a Java application and pass parameters to it, you may encounter a situation where the program runs without any errors but fails to perform its intended action.

Potential Causes

In the example code you provided, you are using the Runtime.getRuntime().exec() method to execute the external program. This method takes an array of strings as its argument, where the first element is the command to execute and the subsequent elements are the arguments to pass to the command.

Working Solution

The issue in your code is that you are not correctly capturing the output of the external program. To obtain the output and check the program's behavior, you can use the following modified code:

<code class="java">Process process = new ProcessBuilder(
    "C:\Users\user\Desktop\program.exe",
    "C:\Users\user\Desktop\images.jpg",
    "C:\Users\user\Desktop\images2.txt"
)
.start();

InputStream is = process.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);

String line;
System.out.printf("Output of running %s is:", Arrays.toString(params));

while ((line = br.readLine()) != null) {
    System.out.println(line);
}</code>

Explanation

In this code, we use the ProcessBuilder class to create a new process that will execute the external program. The start() method is then used to start the process.

To capture the output of the process, we create an InputStream from the process, an InputStreamReader to wrap the InputStream, and a BufferedReader to read lines from the InputStreamReader.

We then use the readLine() method from the BufferedReader to read each line of output from the process. Finally, the output lines are printed using the System.out.println() statement.

By using this approach, you can execute external programs from Java and capture their output, including any errors or messages that they may produce. You can then use this output to further process or display the results.

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