Mockito + PowerMock LinkageError，同时嘲笑系统类
我有这样的代码片段：
@RunWith(PowerMockRunner.class) @PrepareForTest({Thread.class}) public class AllMeasuresDataTest { @Before public void setUp() throws Exception { } @Test public void testGetMeasures() { AllMeasuresData measure = new AllMeasuresData(); assertEquals(measure.getMeasures(), null); HashMap<String, Measure> map = new HashMap<String, Measure>(); measure.setMeasures(map); assertEquals(measure.getMeasures(), map); measure.setMeasures(null); assertEquals(measure.getMeasures(), null); } @Test public void testAllMeasuresData() throws IOException { ClassLoader loader = PowerMockito.mock(ClassLoader.class); Thread threadMock = PowerMockito.mock(Thread.class); Vector<URL> vec = new Vector<URL>(); Mockito.when(loader.getResources("measure")).thenReturn(vec.elements()); Mockito.when(threadMock.getContextClassLoader()).thenReturn(loader); PowerMockito.mockStatic(Thread.class); Mockito.when(Thread.currentThread()).thenReturn(threadMock); ... } } 运行这个testing时，我得到了：
java.lang.LinkageError: loader constraint violation: loader (instance of org/powermock/core/classloader/MockClassLoader) previously initiated loading for a different type with name "javax/management/MBeanServer" at java.lang.ClassLoader.defineClass1(Native Method) at java.lang.ClassLoader.defineClass(ClassLoader.java:791) at java.lang.ClassLoader.defineClass(ClassLoader.java:634) at org.powermock.core.classloader.MockClassLoader.loadUnmockedClass(MockClassLoader.java:201) at org.powermock.core.classloader.MockClassLoader.loadModifiedClass(MockClassLoader.java:149) at org.powermock.core.classloader.DeferSupportingClassLoader.loadClass(DeferSupportingClassLoader.java:67) at java.lang.ClassLoader.loadClass(ClassLoader.java:356) at org.codecover.instrumentation.java.measurement.ProtocolImpl.initializeMBean(ProtocolImpl.java:247) at org.codecover.instrumentation.java.measurement.ProtocolImpl.<init>(ProtocolImpl.java:237) at org.codecover.instrumentation.java.measurement.ProtocolImpl.getInstance(ProtocolImpl.java:185) at measure.CodeCoverCoverageCounter$6ya5ud0ow79ijrr1dvjrp4nxx60qhxeua02ta2fzpmb1d.<clinit>(MeasureCalculatorsHolder.java:146) at measure.MeasureCalculatorsHolder.<clinit>(MeasureCalculatorsHolder.java:17) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:188) at javassist.runtime.Desc.getClassObject(Desc.java:43) at javassist.runtime.Desc.getClassType(Desc.java:152) at javassist.runtime.Desc.getType(Desc.java:122) at javassist.runtime.Desc.getType(Desc.java:78) at algorithm.AllMeasuresDataTest.testGetMeasures(AllMeasuresDataTest.java:26) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:601) at org.junit.internal.runners.TestMethod.invoke(TestMethod.java:66) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:312) at org.junit.internal.runners.MethodRoadie$2.run(MethodRoadie.java:86) at org.junit.internal.runners.MethodRoadie.runBeforesThenTestThenAfters(MethodRoadie.java:94) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.executeTest(PowerMockJUnit44RunnerDelegateImpl.java:296) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit49RunnerDelegateImpl$PowerMockJUnit49MethodRunner.executeTestInSuper(PowerMockJUnit49RunnerDelegateImpl.java:116) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit49RunnerDelegateImpl$PowerMockJUnit49MethodRunner.executeTest(PowerMockJUnit49RunnerDelegateImpl.java:77) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$PowerMockJUnit44MethodRunner.runBeforesThenTestThenAfters(PowerMockJUnit44RunnerDelegateImpl.java:284) at org.junit.internal.runners.MethodRoadie.runTest(MethodRoadie.java:84) at org.junit.internal.runners.MethodRoadie.run(MethodRoadie.java:49) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.invokeTestMethod(PowerMockJUnit44RunnerDelegateImpl.java:209) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.runMethods(PowerMockJUnit44RunnerDelegateImpl.java:148) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl$1.run(PowerMockJUnit44RunnerDelegateImpl.java:122) at org.junit.internal.runners.ClassRoadie.runUnprotected(ClassRoadie.java:34) at org.junit.internal.runners.ClassRoadie.runProtected(ClassRoadie.java:44) at org.powermock.modules.junit4.internal.impl.PowerMockJUnit44RunnerDelegateImpl.run(PowerMockJUnit44RunnerDelegateImpl.java:120) at org.powermock.modules.junit4.common.internal.impl.JUnit4TestSuiteChunkerImpl.run(JUnit4TestSuiteChunkerImpl.java:101) at org.powermock.modules.junit4.common.internal.impl.AbstractCommonPowerMockRunner.run(AbstractCommonPowerMockRunner.java:53) at org.powermock.modules.junit4.PowerMockRunner.run(PowerMockRunner.java:53) at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50) at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683) at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390) at org.codecover.juniteclipse.runner.EclipseTestRunner.main(EclipseTestRunner.java:40)
你知道我怎么能防止这个？ 我也许有另一种方法来模拟这样一段代码：
ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); ... Enumeration<URL> resources = classLoader.getResources(path);
尝试添加这个注释到你的Test类：
@PowerMockIgnore("javax.management.*")
为我工作。
类加载器冲突，使用这个： @PowerMockIgnore("javax.management.*")
让模拟类加载器不加载javax.*. 有用。
克兰德拉德的回答帮助我达到了类似的最终解决scheme。 我最终不得不排除所有的SSL相关的类：
@PowerMockIgnore({"javax.management.*", "org.apache.http.conn.ssl.*", "com.amazonaws.http.conn.ssl.*", "javax.net.ssl.*"})
这可能是一个老话题，但我也遇到了这个问题。 当powermock发现在同一个包中有两个具有相同名称的类（通过不同的依赖关系）时，发现有些java版本无法处理powermockito。
任何高于Java 7_25的版本都会出现此错误。
为了模拟系统类，准备作为testing目标的类，而不是Thread.class 。 PowerMock无法对Thread.class进行testing，因为在JVM启动期间需要它 – 在PowerMock可以testing之前。
仪器工作的方式，一旦一个类被加载，它不能再被注入。
查看PowerMock wiki 。
