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Learn how to stop reading an InputStream after a specific number of bytes using a custom Java class that wraps the InputStream.
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Efficiently Control InputStream Reading: Create a Limited Input Stream Wrapper

When working with input streams in Java, you may encounter scenarios where you need to read only a specific number of bytes from the stream before stopping. This can be particularly important for handling data in manageable chunks, such as when sending data to a BodyPublisher. How can you achieve this? In this guide, we’ll explore how to create a custom input stream that allows you to limit the number of bytes read from an underlying stream.

The Challenge

Imagine you are streaming data to a network or file operation, where you want to process the input in smaller, well-defined segments. For instance, if you have an input stream and you wish to read, say, 100 bytes before stopping, how do you implement this effectively? The answer lies in creating a custom InputStream wrapper.

The Solution: LimitedInputStream

To tackle this challenge, we can create a LimitedInputStream class that extends FilterInputStream. This class will allow you to specify a limit on the number of bytes that can be read at any given time. Below, we break down the implementation of this class.

Class Implementation

Here’s the Java code you need:

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

Components of the Implementation

Constructor: This sets up the input stream and the byte limit. It checks for invalid parameters (like a null stream or a non-positive limit).

read() Methods: The class overrides the read() methods to restrict the number of bytes that can be read. The limit is decreased with each read operation until it reaches zero.

skip() Method: This method allows skipping over bytes while respecting the byte limit.

available() Method: This method ensures that the number of available bytes reported is not greater than the remaining limit.

Example Usage

In the main method, we demonstrate how to use the LimitedInputStream:

Create a ByteArrayInputStream with a sample byte array.

Wrap it using LimitedInputStream, specifying the byte limit (e.g., 100 bytes).

Read data and observe how it respects the imposed limits.

Conclusion

Using the LimitedInputStream approach, you can easily manage how many bytes your application reads from an input stream. This is particularly useful when dealing with large data transfers or processing data in chunks. By implementing your own input stream wrapper, you gain precise control over data handling in your Java applications.

Feel free to try out this code and modify it for your use cases. Happy coding!