Convert APK to JAD

What the APK format is

APK is the installable package format for Android applications, produced by Android Studio, Gradle, and Android packaging tools. Android distributions may provide a single APK or multiple split APKs; developer builds, device backups, and third-party repositories commonly contain APK files.

An APK is a ZIP-based container that normally includes a compiled or binary AndroidManifest.xml, Dalvik/ART bytecode in classes.dex, resources, native libraries, and signing information. Android uses the manifest, DEX code, resources, and framework APIs to install and run the application.

What the JAD format is

JAD is a plain-text Java Application Descriptor used by Java ME phones and emulators. It describes a separate Java ME application JAR and commonly contains MIDlet-Name, MIDlet-Version, MIDlet-Vendor, MIDlet-1, MicroEdition-Configuration, MicroEdition-Profile, MIDlet-Jar-URL, and MIDlet-Jar-Size.

The JAR contains Java ME class files and resources; the JAD supplies installation metadata and identifies that JAR. A JAD is not an executable application, and it cannot run without compatible Java ME code.

Why direct conversion does not work

There is no genuine APK-to-JAD conversion. Android uses DEX bytecode, Android framework APIs, Android application components, and the Dalvik/ART runtime. Java ME uses Java class files, CLDC/MIDP APIs, and the MIDlet lifecycle. A descriptor cannot translate bytecode, Android layouts, permissions, native libraries, or framework dependencies between these platforms.

Renaming app.apk to app.jad, extracting APK contents into a JAR, or copying Android manifest values into a JAD creates an invalid or nonfunctional Java ME package. No reputable online converter can turn an Android application into a working MIDlet; services that claim to do so generally rename, extract, or repackage files without translating the program.

How to create a JAD from an existing Java ME JAR

This procedure applies only when you already have a valid Java ME JAR, including one that happens to be bundled inside an APK. An arbitrary JAR inside an APK is not automatically a Java ME application; check for MIDlet classes and Java ME manifest attributes.

1. Inspect the APK with 7-Zip or the Android platform tools. On a system with unzip, list its contents with unzip -l app.apk and extract them with unzip app.apk -d app_unpacked. Extraction does not convert Android code.
2. Use Apktool when you need to inspect Android resources, the manifest, or disassembled DEX code: apktool d app.apk -o app_decoded. Apktool decodes Android files and produces smali, but it does not produce a Java ME JAR or JAD.
3. If a suitable Java ME JAR is present, use a local JAR-to-JAD utility such as JADMaker, or create the descriptor manually in a plain-text editor. Java ME SDK or Wireless Toolkit packaging tools can also generate descriptors as part of a Java ME build.
4. For manual creation, save a text file beside the JAR with the same base name, for example example.jad beside example.jar:

MIDlet-Name: Example
MIDlet-Version: 1.0
MIDlet-Vendor: Example Vendor
MIDlet-1: Example,,com.example.ExampleMIDlet
MicroEdition-Configuration: CLDC-1.1
MicroEdition-Profile: MIDP-2.0
MIDlet-Jar-URL: example.jar
MIDlet-Jar-Size: 123456

Replace the sample values with metadata supported by the JAR. The class in MIDlet-1 must exist in the JAR and implement the required MIDlet entry point. MIDlet-Jar-Size must be the exact JAR size in bytes, without separators. The URL can be a local filename for sideloading or a server URL for network installation.

An online JAR-to-JAD generator is acceptable only for a non-sensitive, already valid Java ME JAR; it cannot convert an APK. A desktop generator is safer for signed or proprietary files because uploading the archive exposes its contents. Verify the generated fields and JAR size before transferring both files to the phone or emulator.

Compatibility limitations

An Android APK may require Android framework versions, permissions, Google services, native libraries, touchscreen features, or hardware that has no Java ME equivalent. Even source-code decompilation would not produce a portable MIDlet without a substantial rewrite against CLDC/MIDP APIs and a new Java ME build.

For Android installation or archiving, retain the original signed APK or all required split APKs. For a Java ME device, obtain the original matching JAR/JAD release or a separately developed Java ME port; a generated descriptor alone cannot make the Android application compatible.