How Can I Efficiently Append Files to a Zip File in Java?

Appending Files to a Zip File in Java: Exploring Efficient Methods

When working with war files, it's common to extract their contents, add new files, and then create a new war file. However, this process can be time-consuming due to the need for expansion and recompression.

One efficient alternative to consider is appending files to the war file directly. While the Java documentation doesn't provide explicit guidance on this, there are external libraries that enable this functionality.

TrueZip and Similar Libraries

TrueZip is a popular Java library for manipulating zip files. It supports appending files to zip archives, making it a suitable solution for the scenario described. Here's an example using TrueZip:

ZipFile zipFile = new ZipFile("test.war");
zipFile.addFile("new.txt", new File("new.txt"));
zipFile.close();

Java 7 ジップファイルシステム機能

In Java 7, the Zip File System API provides a native mechanism for accessing and manipulating zip files as a file system. This allows for direct writing and modification of files within the zip without having to repackage the entire file.

Map<String, String> env = new HashMap<>();
env.put("create", "true");
Path path = Paths.get("test.zip");
URI uri = URI.create("jar:" + path.toUri());
try (FileSystem fs = FileSystems.newFileSystem(uri, env)) {
  Path nf = fs.getPath("new.txt");
  try (Writer writer = Files.newBufferedWriter(nf, StandardCharsets.UTF_8, StandardOpenOption.CREATE)) {
    writer.write("hello");
  }
}

The Java 7 Zip File System is a powerful and efficient approach for appending files to zip archives. However, for older Java versions, external libraries like TrueZip can fill this functionality gap.

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