spring boot Caused by: java.lang.UnsupportedOperationException: Unsupported class version number [53.0] (maximum 52.0, Java 1.8)

Question

I am currently working on a Spring Boot project which I intend to obfuscate with Proguard. Everything works just fine. But when I try to package the application, I receive this Proguard error

    (Can't process class [META-INF/versions/9/org/apache/logging/log4j/util/ProcessIdUtil.class] (Unsupported class version number [53.0] (maximum 52.0, Java 1.8)))
 [proguard]     at proguard.InputReader.readInput(InputReader.java:188)
 [proguard]     at proguard.InputReader.readInput(InputReader.java:158)
 [proguard]     at proguard.InputReader.readInput(InputReader.java:136)
 [proguard]     at proguard.InputReader.execute(InputReader.java:88)
 [proguard]     at proguard.ProGuard.readInput(ProGuard.java:218)
 [proguard]     at proguard.ProGuard.execute(ProGuard.java:82)
 [proguard]     at proguard.ProGuard.main(ProGuard.java:538)
 [proguard] Caused by: java.io.IOException: Can't process class [META-INF/versions/9/org/apache/logging/log4j/util/ProcessIdUtil.class] (Unsupported class version number [53.0] (maximum 52.0, Java 1.8))
 [proguard]     at proguard.io.ClassReader.read(ClassReader.java:112)
 [proguard]     at proguard.io.FilteredDataEntryReader.read(FilteredDataEntryReader.java:87)
 [proguard]     at proguard.io.FilteredDataEntryReader.read(FilteredDataEntryReader.java:87)
 [proguard]     at proguard.io.JarReader.read(JarReader.java:65)
 [proguard]     at proguard.io.DirectoryPump.readFiles(DirectoryPump.java:65)
 [proguard]     at proguard.io.DirectoryPump.pumpDataEntries(DirectoryPump.java:53)
 [proguard]     at proguard.InputReader.readInput(InputReader.java:184)
 [proguard]     ... 6 more
 [proguard] Caused by: java.lang.UnsupportedOperationException: Unsupported class version number [53.0] (maximum 52.0, Java 1.8)
 [proguard]     at proguard.classfile.util.ClassUtil.checkVersionNumbers(ClassUtil.java:145)
 [proguard]     at proguard.classfile.io.LibraryClassReader.visitLibraryClass(LibraryClassReader.java:89)
 [proguard]     at proguard.classfile.LibraryClass.accept(LibraryClass.java:306)
 [proguard]     at proguard.io.ClassReader.read(ClassReader.java:86)
 [proguard]     ... 12 more
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 01:22 min
[INFO] Finished at: 2018-01-13T13:10:43+01:00
[INFO] Final Memory: 26M/281M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal com.github.wvengen:proguard-maven-plugin:2.0.14:proguard (default) on project ESMANSOFT: Obfuscation failed (result=1) -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException

I have tried so many options but nothing worked. I even tried upgrading to Java 9 but was told proguard does not support java 9. I am using proguard 5.3.3. What is the best way out? Thanks in advance.

You'll need to downgrade your code to Java 8 if you want to use ProGuard. Honestly though, I would just get rid of ProGuard. — Boris the Spider, Jan 13 '18 at 12:20
You are using Java 9 based libraries (in your case Log4j) and ProGuard doesn't support Java 9. You have to downgrade all Java 9 based dependencies. — dur, Jan 13 '18 at 16:34
@NdzembomenyiAruna, It looks like Java version mismatch issue and it's happening for your logging library. Is your logging library compatible with the Java version you're using in your project ?? — Abhishek, Jan 13 '18 at 16:44
I am using spring boot 2.0.0.M7. Even after removing the `code` org.slf4j slf4j-log4j12 `code` It still give same error. It's as if the framework has an internal log4j — Ndzembomenyi Aruna, Jan 14 '18 at 20:46

score 0 · Answer 1 · answered Jan 15 '18 at 02:06

After putting together the users' contributions, I finally used a local copy of the proguard jar file and it worked!!! I created a folder resources/libs/proguard/ and placed the latest proguard.jar inside. In this case proguard6.0beta1. This is the proguard configuration

 <plugin>
            <groupId>com.github.wvengen</groupId>
<artifactId>proguard-maven-plugin</artifactId>

            <executions>
                <execution>
                    <phase>package</phase>
                    <goals><goal>proguard</goal></goals>
                </execution>
            </executions>
            <configuration>
                <proguardVersion>6.0beta1</proguardVersion>
                <injar>${project.build.finalName}.jar</injar>
                <outjar>${project.build.finalName}.jar</outjar>
                <obfuscate>true</obfuscate>
                <proguardInclude>${basedir}/proguard.conf</proguardInclude>
                <libs>
                    <!-- Include main JAVA library required.-->
                    <lib>${java.home}/lib/rt.jar</lib>
                    <!-- Include crypto JAVA library if necessary.-->
                    <lib>${java.home}/lib/jce.jar</lib>

                    <lib>${java.home}/lib/jsse.jar</lib>
                </libs>
            </configuration>
            <dependencies>
                <dependency>
                    <groupId>net.sf.proguard</groupId>
                    <artifactId>proguard-base</artifactId>
                    <version>6.0beta1</version>
                        <scope>system</scope>
        <systemPath>${basedir}/src/main/resources/libs/proguard/proguard.jar</systemPath>
                </dependency>
            </dependencies>

Thanks a million!

score -1 · Answer 2 · answered Aug 01 '18 at 07:30

I've met the question as you too! Fortunately,the problem was solved.

<exclusions>
    <exclusion>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-logging</artifactId>
    </exclusion>
</exclusions>

in spring-boot-starter dependency add this， exclude default logging frame.

it can solve my problem,but i don't know why.

spring boot Caused by: java.lang.UnsupportedOperationException: Unsupported class version number [53.0] (maximum 52.0, Java 1.8)

2 Answers2