NullPointerException：ProGuard，春季启动

Question

I'm getting null pointer exception and have no ideas on how to overcome this issue and obfuscate the code. Do you have any ideas?

I'm working to obfuscate some libraries of a [Maven] Spring-Boot project with Proguard (proguard + proguard-maven-plugin)

Stack trace:

org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal com.github.wvengen:proguard-maven-plugin:2.0.11:proguard (proguard) on project XXX: Execution proguard of goal com.github.wvengen:proguard-maven-plugin:2.0.11:proguard failed.
(...)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution proguard of goal com.github.wvengen:proguard-maven-plugin:2.0.11:proguard failed.
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:110)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:209)
... 19 more
Caused by: java.lang.NullPointerException
at com.github.wvengen.maven.proguard.ProGuardMojo.execute(ProGuardMojo.java:506)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:101)
... 20 more

POM build plugin:

<plugin>
 <groupId>com.github.wvengen</groupId>
 <artifactId>proguard-maven-plugin</artifactId>
 <version>2.0.11</version>
 <executions>
  <execution>
   <id>proguard</id>
   <phase>package</phase>
   <goals>
    <goal>proguard</goal>
   </goals>
  </execution>
 </executions>
 <configuration>
  <obfuscate>true</obfuscate>
  <injar>${project.build.finalName}.jar</injar>
  <outjar>${project.build.finalName}-small.jar</outjar>
  <outputDirectory>${project.build.directory}/proguard</outputDirectory>
  <proguardInclude>${basedir}/proguard.conf</proguardInclude>
  <libs>
   <lib>${java.bootstrap.classes}</lib>
   <lib>${java.cryptographic.extension.classes}</lib>
   <lib>${java.secure.socket.extension.classes}</lib>
  </libs>
  <injarNotExistsSkip>true</injarNotExistsSkip>
  <options>
 </options>
</configuration>
<dependencies>
 <dependency>
  <groupId>net.sf.proguard</groupId>
   <artifactId>proguard-base</artifactId>
   <version>5.2.1</version>
   <scope>runtime</scope>
  </dependency>
 </dependencies>
</plugin>

Answer 1

Given the mentioned stacktrace and looking a the source code of the plugin for the 2.0.11 version, the NullPointerException is thrown in this block of the ProGuardMojo class:

502     if (libs != null) {
503         for (Iterator i = libs.iterator(); i.hasNext();) {
504             Object lib = i.next();
505             args.add("-libraryjars");
506             args.add(fileNameToString(lib.toString()));
507         }
508     }

Which means most probably the lib.toString() is an invocation of a method on a null reference.

From the plugin configuration you mentioned, we can see:

<libs>
   <lib>${java.bootstrap.classes}</lib>
   <lib>${java.cryptographic.extension.classes}</lib>
   <lib>${java.secure.socket.extension.classes}</lib>
</libs>

So, most probably one of these Maven properties is not set, passed as empty/null and causing the error.

You should check whether these properties have a valid value or were supposed to be passed from the command line and was not the case.