当整个maven项目在junit测试下运行时，logger.info抛出空指针异常

Question

以下是示例代码

class Temp
{
    public static int someMethod()
    {
        Logger logger = LoggerFactory.getLogger(Temp.class);
        logger.info("Some information");//NullPointerException
        return 0;
    }
}
class ClassToTest
{
    public int methodToTest()
    {
        Temp tempInstance = new Temp();
        int i = temp.someMethod();
        return i;
    }
}
class TestAClass
{
    ClassToTest classToTestInstance;
    @Before
    public void setUp()
    {
        classToTestInstance = new ClassToTest();
    }
    @Test
    public void testMethodToTest()
    {
        int i = classToTest.methodToTest();
    }
}

这是一个场景。这个测试用例可能会通过。但在实际代码中，当我运行单个测试用例或运行整个测试类时，测试用例会通过，但当我在junit测试下运行maven项目时，它会失败，并出现NullPointerException。我不能发布实际的代码，因为这是一个专有代码。如果有人遇到过这种问题，请指导我。

我运行实际代码时得到的堆栈跟踪：

java.lang.NullPointerException
    at org.slf4j.impl.Log4jLoggerAdapter.info(Log4jLoggerAdapter.java:304)
    at Temp
    at ClassToTest
    at TestAClass
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at mockit.integration.junit4.internal.JUnit4TestRunnerDecorator.executeTestMethod(JUnit4TestRunnerDecorator.java:142)
    at mockit.integration.junit4.internal.JUnit4TestRunnerDecorator.invokeExplosively(JUnit4TestRunnerDecorator.java:71)
    at mockit.integration.junit4.internal.MockFrameworkMethod.invokeExplosively(MockFrameworkMethod.java:40)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
    at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    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.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

Answer 1

此问题是由于logger是Temp类中的static。如果Temp类的实例是早先在另一个测试类中创建的，因此它不能为临时类加载logger，因为它已经加载了。因此，当我们在junit测试下运行整个项目时，它失败了。因为Temp类的logger位于其他测试类中的某个位置，所以已经加载了其他测试类。该问题由mocking、logger和JMockit解决。@SubOptimal感谢您抽出时间。

Answer 2

当Logger对象错误地在类中不是静态时，我得到了这个异常。

Answer 3

我知道这只是一个例子，在实际的代码中可能没有错。不过，我认为最好让你知道。

此处需要进行更正：

class ClassToTest
{
    public int methodToTest()
    {
        Temp tempInstance = new Temp(); 
        // there is no need of an instance here since the method is static.
        
        int i = Temp.someMethod(); // was temp.someMethod()
        return i;
    }
}

我建议在您的Temp.class中使记录器静态，如下所示：

class Temp
{
    private static Logger logger = LoggerFactory.getLogger(Temp.class);
    public static int someMethod()
    {
        logger.info("Some information");
        return 0;
    }
}

Answer 4

即使我遇到了同样的问题，我也将这段代码添加到了我的类中（在本例中为类Temp）

public class Temp {
  private static final Logger logger = Logger.getLogger(Temp.class);
  //Write your code
}