How to Obfuscate Java Applications with ProGuard: Step‑by‑Step Guide

Compilation

Compilation simply runs the code, turning .java files into .class files.

Decompilation

Decompilation reverses compiled .class files in a jar/war package back to readable source code, e.g., using JD‑GUI.

Obfuscation

Obfuscation hides the real source code after decompilation; the article demonstrates using ProGuard.

Procedure

The obfuscation process consists of two steps.

Step 1: Add proguard.cfg

Create a file named proguard.cfg in the project root with the following configuration:

# Specify Java version
-target 1.8
# Disable shrinking
-dontshrink
# Disable optimization
-dontoptimize
# Do not use mixed case class names
-dontusemixedcaseclassnames
# Use unique class member names
-useuniqueclassmembernames
# Adapt class strings
-adaptclassstrings

# Keep attributes for exceptions, annotations, etc.
-keepattributes Exceptions,InnerClasses,Signature,Deprecated,SourceFile,LineNumberTable,*Annotation*,EnclosingMethod
-keepnames interface ** { *; }
-keepparameternames
-keepclassmembers enum * { *; }
-keepclassmembers class * {
    @org.springframework.context.annotation.Bean *;
    @org.springframework.beans.factory.annotation.Autowired *;
    @org.springframework.beans.factory.annotation.Value *;
    @org.springframework.stereotype.Service *;
    @org.springframework.stereotype.Component *;
}
-ignorewarnings
-dontnote
-printconfiguration
-keep public class com.example.myproguarddemo.MyproguarddemoApplication {
    public static void main(java.lang.String[]);
}

Step 2: Configure Maven ProGuard plugin

Add the ProGuard plugin to the build section of pom.xml:

<build>
    <plugins>
        <plugin>
            <groupId>com.github.wvengen</groupId>
            <artifactId>proguard-maven-plugin</artifactId>
            <version>2.6.0</version>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals>
                        <goal>proguard</goal>
                    </goals>
                </execution>
            </executions>
            <configuration>
                <injar>${project.build.finalName}.jar</injar>
                <outjar>${project.build.finalName}.jar</outjar>
                <obfuscate>true</obfuscate>
                <proguardInclude>${project.basedir}/proguard.cfg</proguardInclude>
                <libs>
                    <lib>${java.home}/lib/rt.jar</lib>
                    <lib>${java.home}/lib/jce.jar</lib>
                    <lib>${java.home}/lib/jsse.jar</lib>
                </libs>
                <inLibsFilter>!META-INF/**,!META-INF/versions/9/**.class</inLibsFilter>
                <outputDirectory>${project.basedir}/target</outputDirectory>
                <options>
                    <!-- additional options can be placed here -->
                </options>
            </configuration>
        </plugin>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
            <executions>
                <execution>
                    <goals>
                        <goal>repackage</goal>
                    </goals>
                    <configuration>
                        <mainClass>com.example.myproguarddemo.MyproguarddemoApplication</mainClass>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

After adding these configurations, run mvn package. The build will compile, obfuscate, and package the jar. The resulting jar contains obfuscated bytecode, making reverse engineering difficult.