Скачать или смотреть How to Input to a Started Process with ProcessBuilder in Java

Find out how to successfully send inputs to a running process using Java's `ProcessBuilder`. Learn the crucial step of flushing your output stream for effective communication.
---
This video is based on the question https://stackoverflow.com/q/73090013/ asked by the user 'Petrov Crowford' ( https://stackoverflow.com/u/19606474/ ) and on the answer https://stackoverflow.com/a/73090049/ provided by the user 'shazin' ( https://stackoverflow.com/u/1768226/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to make an input to a started process with ProcessBuilder?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Input to a Started Process with ProcessBuilder in Java

When working with external processes in Java, you might encounter situations where you need to send inputs to a program that operates continuously after being launched. This scenario can be tricky, especially when using ProcessBuilder to manage these processes. In this post, we will explore how to effectively send input to a started process, ensuring your commands reach their destination successfully.

The Problem: Sending Input to a Running Process

Suppose you have a closed-source executable that takes a string as input and returns its hashing. However, rather than taking command-line arguments at startup, it waits for inputs continuously while running. Here’s a simplified version of the code you might use to execute it:

[[See Video to Reveal this Text or Code Snippet]]

Upon executing this snippet, you’ve noticed that the output doesn’t reflect the input you provided. This has led to the question: How can you successfully send inputs to a running process?

The Solution: Flushing the Output Stream

While your approach to sending input was mostly correct, a crucial step was overlooked. After writing to the output stream, you must flush it to ensure the data is actually sent to the process. Flushing the stream clears the buffer and transfers the data to wherever it is intended. Here’s how you can implement this solution:

Step-by-Step Implementation

Write to the Output Stream: First, you will write the input string exactly as before.

Flush the Output Stream: After writing, you should call the flush() method on the PrintWriter object.

Read the Process Output: Once the input has been sent, you can read the output from the process.

Here’s the revised code that incorporates these changes:

[[See Video to Reveal this Text or Code Snippet]]

Additional Tips

Error Handling: Always implement error handling when dealing with processes to catch any exceptions that may occur.

Close Resources: Ensure you close stream and process resources to avoid memory leaks.

Multi-line Inputs: If you need to send multiple lines of input, continue writing to the stream and flush it after each input for best practices.

Conclusion

Sending inputs to a process started with ProcessBuilder in Java requires careful management of the output stream. Flushing the stream after writing is essential for transmitting your data. By following the outlined steps and incorporating the flush operation, you can ensure the process receives and processes your input effectively. With this knowledge, you're now equipped to manage inter-process communication more efficiently in Java.

If you have any more questions or need further clarification, feel free to reach out!