JD-Core

JD-Core is a JAVA decompiler written in JAVA.

• Java Decompiler project home page: http://java-decompiler.github.io
• JD-Core source code: https://github.com/java-decompiler/jd-core
• Jitpack maven repository: https://jitpack.io/

Description

JD-Core is a standalone JAVA library containing the JAVA decompiler of "Java Decompiler project". It support Java 1.1.8 to Java 12.0, including Lambda expressions, method references and default methods. JD-Core is the engine of JD-GUI.

Strategy and goals

• Pursuing strategy described in this research paper : The Strengths and Behavioral Quirks of Java Bytecode Decompilers
• Improved recompilation of decompiled source codes
• Decompiling and recompiling without any errors :
  • commons-io:commons-io:2.11.0
  • commons-codec:commons-codec:1.15
  • org.apache.commons:commons-collections4:4.4
  • org.apache.commons:commons-lang3:3.12.0
  • org.apache.logging.log4j:log4j-core:2.20.0
  • junit:junit:4.13.2
  • and more ... (check unit tests)

How to build JD-Core ?

> git clone https://github.com/java-decompiler/jd-core.git
> cd jd-core
> ./gradlew build

generate "build/libs/jd-core-x.y.z.jar"

How to use JD-Core ?

1. Implement the org.jd.core.loader.Loader interface,
2. Implement the org.jd.core.printer.Printer interface,
3. And call the method "decompile(loader, printer, internalTypeName);"

Example

1. Implement the Loader interface:

Loader loader = new Loader() {
    @Override
    public byte[] load(String internalName) throws IOException {
        InputStream is = this.getClass().getResourceAsStream("/" + internalName + ".class");

        if (is == null) {
            return null;
        } else {
            try (InputStream in=is; ByteArrayOutputStream out=new ByteArrayOutputStream()) {
                byte[] buffer = new byte[1024];
                int read = in.read(buffer);

                while (read > 0) {
                    out.write(buffer, 0, read);
                    read = in.read(buffer);
                }

                return out.toByteArray();
            }
        }
    }

    @Override
    public boolean canLoad(String internalName) {
        return this.getClass().getResource("/" + internalName + ".class") != null;
    }
};

2. Implement the Printer interface

Printer printer = new Printer() {
    protected static final String TAB = "  ";
    protected static final String NEWLINE = "\n";

    protected int indentationCount = 0;
    protected StringBuilder sb = new StringBuilder();

    @Override public String toString() { return sb.toString(); }

    @Override public void start(int maxLineNumber, int majorVersion, int minorVersion) {}
    @Override public void end() {}

    @Override public void printText(String text) { sb.append(text); }
    @Override public void printNumericConstant(String constant) { sb.append(constant); }
    @Override public void printStringConstant(String constant, String ownerInternalName) { sb.append(constant); }
    @Override public void printKeyword(String keyword) { sb.append(keyword); }
    @Override public void printDeclaration(int type, String internalTypeName, String name, String descriptor) { sb.append(name); }
    @Override public void printReference(int type, String internalTypeName, String name, String descriptor, String ownerInternalName) { sb.append(name); }

    @Override public void indent() { this.indentationCount++; }
    @Override public void unindent() { this.indentationCount--; }

    @Override public void startLine(int lineNumber) { for (int i=0; i<indentationCount; i++) sb.append(TAB); }
    @Override public void endLine() { sb.append(NEWLINE); }
    @Override public void extraLine(int count) { while (count-- > 0) sb.append(NEWLINE); }

    @Override public void startMarker(int type) {}
    @Override public void endMarker(int type) {}
};

3. And call the method "decompile(loader, printer, internalTypeName);"

ClassFileToJavaSourceDecompiler decompiler = new ClassFileToJavaSourceDecompiler();

decompiler.decompile(loader, printer, "path/to/YourClass");

String source = printer.toString();

License

Released under the GNU GPL v3.