不支持的major.minor版本51.0在pom中使用1.6而对于一个JUnit使用openjdk6时出错

Question

我正在使用Travis CI来构建我的代码.我得到了不受支持的主要小错误.我知道当编译版本比执行版本更旧时会发生此错误.但我在我的pom文件中将编译版本设置为1.6,而Travis CI也使用openjdk6执行它.所以,我没有看到任何java版本的差异问题.我无法在pom中设置我的java路径,因为我在不同的服务器上使用它,即我的计算机,travis和heroku.所以它们可能不同,所以我不想在POM中设置它.您可以在https://travis-ci.org/santoshkt/cdetsd123上看到travis失败.任何指针都表示赞赏.此外,如果您看到下面aoltest.RegisterTest的内容已通过但aoltest.RegisterServiceTest失败.

Running aoltest.RegisterTest
Tests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.03 sec
Running aoltest.RegisterServiceTest
Tests run: 2, Failures: 0, Errors: 2, Skipped: 0, Time elapsed: 0.025 sec <<< FAILURE!
testProcessRegistration1(aoltest.RegisterServiceTest)  Time elapsed: 0.023 sec  <<< ERROR!
java.lang.UnsupportedClassVersionError: javax/servlet/http/HttpServletRequest : Unsupported major.minor version 51.0
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:643)
    at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
    at java.net.URLClassLoader.defineClass(URLClassLoader.java:277)
    at java.net.URLClassLoader.access$000(URLClassLoader.java:73)
    at java.net.URLClassLoader$1.run(URLClassLoader.java:212)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:323)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:268)
    at aoltest.RegisterServiceTest.testProcessRegistration1(RegisterServiceTest.java:42)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:622)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:44)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:180)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:41)
    at org.junit.runners.ParentRunner$1.evaluate(ParentRunner.java:173)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:220)
    at org.apache.maven.surefire.junit4.JUnit4Provider.execute(JUnit4Provider.java:252)
    at org.apache.maven.surefire.junit4.JUnit4Provider.executeTestSet(JUnit4Provider.java:141)
    at org.apache.maven.surefire.junit4.JUnit4Provider.invoke(JUnit4Provider.java:112)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:622)
    at org.apache.maven.surefire.util.ReflectionUtils.invokeMethodWithArray(ReflectionUtils.java:189)
    at org.apache.maven.surefire.booter.ProviderFactory$ProviderProxy.invoke(ProviderFactory.java:165)
    at org.apache.maven.surefire.booter.ProviderFactory.invokeProvider(ProviderFactory.java:85)
    at org.apache.maven.surefire.booter.ForkedBooter.runSuitesInProcess(ForkedBooter.java:115)
    at org.apache.maven.surefire.booter.ForkedBooter.main(ForkedBooter.java:75)

Answer 1

出现此问题的原因是您依赖的3.1 servlet-api .jar文件是使用JDK7构建的,并且它包含的类使用仅在JDK7或更高版本上兼容的类文件格式.

例如,如果使用JDK 6编译项目,则在项目中使用以下Maven/gradle/ant + ivy/sbt/etc依赖项将失败:

<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>3.1.0</version>
</dependency>

根据Java EE 7规范 - 包括Servlet 3.1规范 - 需要JDK7来运行基于Java EE 7的容器和应用程序.因此,编译和分发3.1 servlet-api .jars到Maven central(核心Servlet API团队？)的人没有理由/需要确保JDK 6二进制兼容性.

将上述依赖项降级为版本3.0.1可以解决您的问题.