Java Class Restorer

Java Class Restorer is a utility for scanning binary files, directories, or JAR archives to locate and restore embedded Java .class files.
It detects the standard Java class file magic number (0xCAFEBABE), attempts to reconstruct valid class definitions using ASM, and writes the recovered classes into a new JAR file.

Requirements

• Java 24 (JDK 24 or newer)
• The provided JAR already contains all required libraries — no additional downloads are needed.
• Any modern IDE (IntelliJ IDEA .iml project file is included) or command line.

Running

From the command line:

java -jar jcr-.jar <input_file|dir|jar> [output_jar] [max_class_size] [package_filter]

Arguments

Argument	Required	Description
input_file/dir/jar	Yes	Path to a file, directory, or JAR to scan.
output_jar	No	Output JAR file name/path. Defaults to <input>-restored.jar.
max_class_size	No	Maximum class size in bytes to attempt restoring. Default: 20480.
package_filter	No	Only restore classes whose internal name starts with this package (dot or slash notation).

Examples

Restore classes from a JAR:

java -jar java-class-restorer.jar input.jar

Restore from a binary dump, limit class size to 10 KB, and filter to com.example package:

java -jar java-class-restorer.jar dump.bin restored.jar 10240 com.example

Scan a directory recursively:

java -jar java-class-restorer.jar ./data

Output

• Restored JAR — contains all successfully reconstructed .class files.
• restore.log — detailed log of the process, including:
  • Found magic signatures
  • Restored class names
  • Skipped duplicates
  • Errors and warnings

Notes

• This project is configured for Java 24. Make sure your JAVA_HOME points to JDK 24.
• All dependencies are already included in the JAR — you can run it directly without building.
• The .iml file is provided for IntelliJ IDEA users; simply open the project and run App.main().

License

MIT License — see LICENSE for details.