The ProGuard tool shrinks, optimizes, and obfuscates your code by removing unused code and
renaming classes, fields, and methods with semantically obscure names. The result is a smaller
.apk file that is more difficult to reverse engineer. Because ProGuard makes your
application harder to reverse engineer, it is important that you use it
when your application utilizes features that are sensitive to security like when you are
Licensing Your Applications.
ProGuard is integrated into the Android build system, so you do not have to invoke it manually. ProGuard runs only when you build your application in release mode, so you do not have to deal with obfuscated code when you build your application in debug mode. Having ProGuard run is completely optional, but highly recommended.
This document describes how to enable and configure ProGuard as well as use the
retrace tool to decode obfuscated stack traces.
When you create an Android project, a
proguard.cfg file is automatically
generated in the root directory of the project. This file defines how ProGuard optimizes and
obfuscates your code, so it is very important that you understand how to customize it for your
needs. The default configuration file only covers general cases, so you most likely have to edit
it for your own needs. See the following section about Configuring ProGuard for information on
customizing the ProGuard configuration file.
To enable ProGuard so that it runs as part of an Ant or Eclipse build, set the
proguard.config property in the
file. The path can be an absolute path or a path relative to the project's root.
If you left the
proguard.cfg file in its default location (the project's root directory),
you can specify its location like this:
You can also move the the file to anywhere you want, and specify the absolute path to it:
When you build your application in release mode, either by running
ant release or
by using the Export Wizard in Eclipse, the build system automatically checks to see if
proguard.config property is set. If it is, ProGuard automatically processes
the application's bytecode before packaging everything into an
.apk file. Building in debug mode
does not invoke ProGuard, because it makes debugging more cumbersome.
ProGuard outputs the following files after it runs:
- Describes the internal structure of all the class files in the
- Lists the mapping between the original and obfuscated class, method, and field names. This file is important when you receive a bug report from a release build, because it translates the obfuscated stack trace back to the original class, method, and member names. See Decoding Obfuscated Stack Traces for more information.
- Lists the classes and members that are not obfuscated
- Lists the code that was stripped from the
<project_root>/bin/proguardif you are using Ant.
<project_root>/proguardif you are using Eclipse.
- a class that is referenced only in the
- a method called from JNI
- dynamically referenced fields and methods
These files are located in the following directories:
Caution: Every time you run a build in release mode, these files are overwritten with the latest files generated by ProGuard. Save a copy of them each time you release your application in order to de-obfuscate bug reports from your release builds. For more information on why saving these files is important, see Debugging considerations for published applications.
For some situations, the default configurations in the
proguard.cfg file will
suffice. However, many situations are hard for ProGuard to analyze correctly and it might remove code
that it thinks is not used, but your application actually needs. Some examples include:
proguard.cfg file tries to cover general cases, but you might
encounter exceptions such as
ClassNotFoundException, which happens when ProGuard
strips away an entire class that your application calls.
You can fix errors when ProGuard strips away your code by adding a
-keep line in
proguard.cfg file. For example:
-keep public class <MyClass>
There are many options and considerations when using the
-keep option, so it is
highly recommended that you read the ProGuard
Manual for more information about customizing your configuration file. The Overview of Keep options and
are particularly helpful. The Troubleshooting section of the
ProGuard Manual outlines other common problems you might encounter when your code gets stripped
Decoding Obfuscated Stack Traces
When your obfuscated code outputs a stack trace, the method names are obfuscated, which makes
debugging hard, if not impossible. Fortunately, whenever ProGuard runs, it outputs a
<project_root>/bin/proguard/mapping.txt file, which shows you the original
class, method, and field names mapped to their obfuscated names.
retrace.bat script on Windows or the
retrace.sh script on Linux
or Mac OS X can convert an obfuscated stack trace to a readable one. It is located in the
<sdk_root>/tools/proguard/ directory. The syntax for executing the
retrace tool is:
retrace.bat|retrace.sh [-verbose] mapping.txt [<stacktrace_file>]
retrace.bat -verbose mapping.txt obfuscated_trace.txt
If you do not specify a value for <stacktrace_file>, the
retrace tool reads
from standard input.
Debugging considerations for published applications
mapping.txt file for every release that you publish to your users.
By retaining a copy of the
mapping.txt file for each release build,
you ensure that you can debug a problem if a user encounters a bug and submits an obfuscated stack trace.
mapping.txt file is overwritten every time you do a release build, so you must be
careful about saving the versions that you need.
For example, say you publish an application and continue developing new features of
the application for a new version. You then do a release build using ProGuard soon after. The
build overwrites the previous
mapping.txt file. A user submits a bug report
containing a stack trace from the application that is currently published. You no longer have a way
of debugging the user's stack trace, because the
mapping.txt file associated with the version
on the user's device is gone. There are other situations where your
mapping.txt file can be overwritten, so
ensure that you save a copy for every release that you anticipate you have to debug.
How you save the
mapping.txt file is your decision. For example, you can rename them to
include a version or build number, or you can version control them along with your source