Скачать или смотреть Preventing DocumentBuilderFactory from Closing Your InputStream: A Java Solution

Learn how to keep your InputStream open when using DocumentBuilderFactory in Java with our comprehensive guide and example solutions.
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How to Prevent DocumentBuilderFactory from Closing Your InputStream

When working with XML files in Java, DocumentBuilderFactory is a powerful tool for parsing. However, one common issue that developers face is that DocumentBuilderFactory closes the underlying InputStream once the parse method is called. This can cause problems, particularly if you need to process the stream further after parsing. In this guide, we will explore how to handle this problem effectively.

The Problem Explained

When you call the parse method of DocumentBuilderFactory using an InputStream, the behavior of automatically closing the stream can be a significant obstacle. In the provided example, the user attempted to create a wrapper class called UncloseableInputStream. Although the intention was to prevent the closure of the stream, the implementation did not work as expected.

The main points to note about this challenge are:

Reason for Closures: The parse method is designed to free resources, and closing the InputStream is part of its cleanup process.

Need for Further Processing: If you need to read from the stream again after parsing, the closure disrupts the workflow because the stream becomes unavailable.

Solution Overview

A recommended approach to bypass the issue is to duplicate the InputStream before parsing. Using a separate InputStream for parsing keeps the original one intact, allowing for further processing down the road. Here's a structured breakdown of how to implement this solution.

Step-by-Step Implementation

Use a BufferedInputStream: This is one way of duplicating the InputStream effectively. It allows you to mark how much of the stream can be reread.

Mark the Stream: Before parsing, use the mark method on the input stream to save the current position.

Reset after Parsing: After parsing the XML, use the reset method to return to the marked position if you need to read again.

Here's how you would typically set this up:

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

Why This Works

BufferedInputStream: By wrapping your original InputStream in a BufferedInputStream, you can take advantage of its ability to mark and reset the stream.

Mark and Reset Methods: These methods provide a way to rewind the stream to a prior position, thus allowing you to read from it multiple times without losing data.

Conclusion

In summary, while DocumentBuilderFactory closes the InputStream post-parsing, you can successfully avoid this issue by using a BufferedInputStream to create a duplicable stream that can be easily reset. This solution keeps your XML parsing logic intact while allowing for further processing of the stream afterward. With this guide, you should be well-equipped to handle similar issues in your Java applications.

Feel free to share your thoughts or experiences regarding this problem in the comments below!