通过枚举对Singleton进行单元测试将抛出java.lang.NoClassDefoundError

Question

这很奇怪，我不知道该如何解释清楚。请耐心听我说，请查看代码片段以了解详细信息。

我使用枚举实现了一个单例。枚举有一个私有构造函数，在构造对象之前，我只在其中执行很少的操作和验证。对于所有这些验证，我将抛出一些异常（如IllegalArgumentException）。

我的测试用例包括针对负面和正面场景的测试。每当有两个以上的测试用例混合了负面和正面的测试用例时，我就会得到以下异常:java.lang.NoClassDefoundError：Could not initialize class com.blah.blah.singletonClass。请检查下面的完整代码。我正在使用以下技术堆栈：

JDK 1.7_51
Spring 4.0.0.RELEASE
testng 6.8.7

public enum SingletonUsingEnum {
  INSTANCE;

  // Logger
  private final Logger logger = LoggerFactory.getLogger(SingletonUsingEnum.class);

  private SingletonUsingEnum() {
    final MyConfig myConfig = MyConfigManager.getMyConfig();
    if(myConfig == null) {
      throw new IllegalArgumentException("MyConfig is null");
    }

    if(StringUtils.isBlank(myConfig.getConfigValue())) {
      throw new IllegalArgumentException("myConfig.configValue value null/empty");
    }

    if(StringUtils.isBlank(myConfig.getOtherConfigValue())) {
      throw new IllegalArgumentException("myConfig.otherConfigValue null/empty");
    }

    logger.info("This is a singleton using enum");
  } 
}

MyConfig.java

public class MyConfig {
  private String configValue;
  private String otherConfigValue;

  public MyConfig(final String configValue, final String otherConfigValue) {
    this.configValue = configValue;
    this.otherConfigValue = otherConfigValue;
  }

  public String getConfigValue() {
    return configValue;
  }

  public String getOtherConfigValue() {
    return otherConfigValue;
  } 
}

MyConfigManager.java

public class MyConfigManager {
  private final static ConcurrentMap myConfigHolder = new ConcurrentHashMap();

  public static void registerMyConfig(final MyConfig myConfig) {
    myConfigHolder.put("myConfig", myConfig);
  }

  public static MyConfig getMyConfig() {
    return myConfigHolder.get("myConfig");
  }

  public static void clearAll() {
    myConfigHolder.clear();
  }
}

SingletonusingEnumTest.java

@ContextConfiguration(classes = {SingletonUsingEnumTest.SpringConfig.class})
public class SingletonUsingEnumTest extends AbstractTestNGSpringContextTests {
  // Logger
  private static final Logger logger = LoggerFactory.getLogger(SingletonUsingEnumTest.class);

  @AfterMethod
  public void cleanUp() {
    MyConfigManager.clearAll();
  }

  @Test(expectedExceptions = {IllegalArgumentException.class, ExceptionInInitializerError.class})
  public void nullMyConfig() {
    MyConfigManager.registerMyConfig(new MyConfig("", ""));
    final SingletonUsingEnum singleton = SingletonUsingEnum.INSTANCE;
  }

  @Test
  public void validMyConfig_nullConfigValue() {
    MyConfigManager.registerMyConfig(new MyConfig("", "b"));
    final SingletonUsingEnum singleton = SingletonUsingEnum.INSTANCE;
  }

  @Test(dependsOnMethods = {"nullMyConfig"})
  public void allValidData() {
    MyConfigManager.registerMyConfig(new MyConfig("a", "b"));
    final SingletonUsingEnum singleton = SingletonUsingEnum.INSTANCE;
  }

  @Configuration
  @EnableAspectJAutoProxy(proxyTargetClass = true)
  public static class SpringConfig {

  }
}

[TestNG] Running:
  /private/var/folders/l6/hmmqvjpj13ggmyc69sk1s5740000gn/T/testng-eclipse-135911498/testng-customsuite.xml

PASSED: nullMyConfig
FAILED: validMyConfig_nullConfigValue
java.lang.NoClassDefFoundError: Could not initialize class com.demo.singleton.SingletonUsingEnum
    at com.demo.singleton.SingletonUsingEnumTest.validMyConfig_nullConfigValue(SingletonUsingEnumTest.java:38)
    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:606)
    at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:84)
    at org.testng.internal.MethodInvocationHelper$1.runTestMethod(MethodInvocationHelper.java:200)
    at org.springframework.test.context.testng.AbstractTestNGSpringContextTests.run(AbstractTestNGSpringContextTests.java:157)
    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:606)
    at org.testng.internal.MethodInvocationHelper.invokeHookable(MethodInvocationHelper.java:212)
    at org.testng.internal.Invoker.invokeMethod(Invoker.java:707)
    at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:901)
    at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1231)
    at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:127)
    at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:111)
    at org.testng.TestRunner.privateRun(TestRunner.java:767)
    at org.testng.TestRunner.run(TestRunner.java:617)
    at org.testng.SuiteRunner.runTest(SuiteRunner.java:334)
    at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:329)
    at org.testng.SuiteRunner.privateRun(SuiteRunner.java:291)
    at org.testng.SuiteRunner.run(SuiteRunner.java:240)
    at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
    at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
    at org.testng.TestNG.runSuitesSequentially(TestNG.java:1224)
    at org.testng.TestNG.runSuitesLocally(TestNG.java:1149)
    at org.testng.TestNG.run(TestNG.java:1057)
    at org.testng.remote.RemoteTestNG.run(RemoteTestNG.java:111)
    at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:204)
    at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:175)

FAILED: allValidData
java.lang.NoClassDefFoundError: Could not initialize class com.demo.singleton.SingletonUsingEnum
    at com.demo.singleton.SingletonUsingEnumTest.allValidData(SingletonUsingEnumTest.java:44)
    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:606)
    at org.testng.internal.MethodInvocationHelper.invokeMethod(MethodInvocationHelper.java:84)
    at org.testng.internal.MethodInvocationHelper$1.runTestMethod(MethodInvocationHelper.java:200)
    at org.springframework.test.context.testng.AbstractTestNGSpringContextTests.run(AbstractTestNGSpringContextTests.java:157)
    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:606)
    at org.testng.internal.MethodInvocationHelper.invokeHookable(MethodInvocationHelper.java:212)
    at org.testng.internal.Invoker.invokeMethod(Invoker.java:707)
    at org.testng.internal.Invoker.invokeTestMethod(Invoker.java:901)
    at org.testng.internal.Invoker.invokeTestMethods(Invoker.java:1231)
    at org.testng.internal.TestMethodWorker.invokeTestMethods(TestMethodWorker.java:127)
    at org.testng.internal.TestMethodWorker.run(TestMethodWorker.java:111)
    at org.testng.TestRunner.privateRun(TestRunner.java:767)
    at org.testng.TestRunner.run(TestRunner.java:617)
    at org.testng.SuiteRunner.runTest(SuiteRunner.java:334)
    at org.testng.SuiteRunner.runSequentially(SuiteRunner.java:329)
    at org.testng.SuiteRunner.privateRun(SuiteRunner.java:291)
    at org.testng.SuiteRunner.run(SuiteRunner.java:240)
    at org.testng.SuiteRunnerWorker.runSuite(SuiteRunnerWorker.java:52)
    at org.testng.SuiteRunnerWorker.run(SuiteRunnerWorker.java:86)
    at org.testng.TestNG.runSuitesSequentially(TestNG.java:1224)
    at org.testng.TestNG.runSuitesLocally(TestNG.java:1149)
    at org.testng.TestNG.run(TestNG.java:1057)
    at org.testng.remote.RemoteTestNG.run(RemoteTestNG.java:111)
    at org.testng.remote.RemoteTestNG.initAndRun(RemoteTestNG.java:204)
    at org.testng.remote.RemoteTestNG.main(RemoteTestNG.java:175)


===============================================
    Default test
    Tests run: 3, Failures: 2, Skips: 0
===============================================


===============================================
Default suite
Total tests run: 3, Failures: 2, Skips: 0
===============================================

[TestNG] Time taken by org.testng.reporters.JUnitReportReporter@6997f7f4: 8 ms
[TestNG] Time taken by org.testng.reporters.XMLReporter@4474c7fe: 14 ms
[TestNG] Time taken by [FailedReporter passed=0 failed=0 skipped=0]: 6 ms
[TestNG] Time taken by org.testng.reporters.SuiteHTMLReporter@395e7bc4: 14 ms
[TestNG] Time taken by org.testng.reporters.EmailableReporter2@71419cf7: 5 ms
[TestNG] Time taken by org.testng.reporters.jq.Main@6015eb5a: 31 ms

Answer 1

您的测试尝试使用您的单例。因此JVM加载并初始化枚举。作为此过程的一部分，它调用您的构造函数来初始化唯一枚举实例。构造函数引发异常，从而阻止正确加载类。

一旦JVM尝试加载类但失败了，它就不会再尝试加载它了。

单例是一种反模式。在一个类加载时急切地初始化的单例中进行这种导致异常的过程是一个非常糟糕的主意。