执行Maven Install打包的时候，出现以下错误信息：

[proguard] ProGuard, version 4.4
 [proguard] Reading input...
 [proguard] Reading program war [F:\Workspaces\pro-test\target\pro-test-0.0.1-SNAPSHOT.war] (filtered)
 [proguard] java.io.IOException: Can't read [proguard.ClassPathEntry@5ef04b5] (Can't process class [WEB-INF/classes/pro/test/First.class] (Unsupported version number [52.0] for class format))
 [proguard]     at proguard.InputReader.readInput(InputReader.java:230)
 [proguard]     at proguard.InputReader.readInput(InputReader.java:200)
 [proguard]     at proguard.InputReader.readInput(InputReader.java:178)
 [proguard]     at proguard.InputReader.execute(InputReader.java:78)
 [proguard]     at proguard.ProGuard.readInput(ProGuard.java:195)
 [proguard]     at proguard.ProGuard.execute(ProGuard.java:78)
 [proguard]     at proguard.ProGuard.main(ProGuard.java:499)

问题分析

产生该错误的原因是因为项目使用的Java（JDK）版本比较高，而ProGuard, version 4.4支持的版本（最高到1.6），所以产生该问题。

解决方案

以问题的解决方案与“Error: Unsupported java version ‘1.8’ in line 2 of file ‘proguard.conf’”的一致：

改用com.github.wvengen的proguard-maven-plugin
repo地址为：http://repo1.maven.org/maven2/com/github/wvengen/proguard-maven-plugin/
完整示例如下：

            <plugin>
                <groupId>com.github.wvengen</groupId>
                <artifactId>proguard-maven-plugin</artifactId>
                <version>2.0.10</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>proguard</goal>
                        </goals>
                    </execution>
                </executions>
                <configuration>
                    <proguardVersion>5.2</proguardVersion>
                    <obfuscate>true</obfuscate>
                    <proguardInclude>${basedir}/proguard.conf</proguardInclude> 
                    <!-- 添加依赖，这里你可以按你的需要修改 -->
                    <libs>
                        <lib>${java.home}/lib/rt.jar</lib>
                        <lib>E:/tomcat-8.0/lib/jsp-api.jar</lib>
                        <lib>E:/tomcat-8.0/lib/servlet-api.jar</lib>
                    </libs>
                    <addMavenDescriptor>false</addMavenDescriptor>
                    <injar>${project.build.finalName}.war</injar>
                    <outjar>${project.build.finalName}-pg.war</outjar>
                    <outputDirectory>${project.build.directory}</outputDirectory>
                </configuration>
                <dependencies> 
                    <!-- 使用5.2版本来混淆 -->
                    <dependency>
                        <groupId>net.sf.proguard</groupId>
                        <artifactId>proguard-base</artifactId>  
                        <version>5.2</version>
                        <scope>runtime</scope>
                    </dependency>
                </dependencies>
            </plugin>