java - 尝试更改静态非最终字段会引发 IllegalArgument 异常

Question

具有私有(private)静态非最终字段的类

package sample;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

public class App {
   private static Logger logger = LoggerFactory.getLogger(App.class);

   public void doSomething() {
      logger.error("Cannot do something");
   }
}

尝试通过反射设置该字段

package sample;

import org.apache.logging.log4j.core.Logger;
import org.junit.jupiter.api.Test;
import org.springframework.test.util.ReflectionTestUtils;

import static org.mockito.Mockito.mock;

public class AppTest {

    @Test
    public void doSomething() throws Exception {
        App app = new App();

        Logger mockedLogger = mock(Logger.class);

        ReflectionTestUtils.setField(App.class, "logger", mockedLogger);
    }
}

导致 IllegalArgumentException

Can not set static org.slf4j.Logger field sample.App.logger to org.apache.logging.log4j.core.Logger$MockitoMock$1185285221
java.lang.IllegalArgumentException: Can not set static org.slf4j.Logger field sample.App.logger to org.apache.logging.log4j.core.Logger$MockitoMock$1185285221
    at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:167)
    at sun.reflect.UnsafeFieldAccessorImpl.throwSetIllegalArgumentException(UnsafeFieldAccessorImpl.java:171)
    at sun.reflect.UnsafeStaticObjectFieldAccessorImpl.set(UnsafeStaticObjectFieldAccessorImpl.java:79)
    at java.lang.reflect.Field.set(Field.java:764)
    at org.springframework.util.ReflectionUtils.setField(ReflectionUtils.java:633)

根据调用方法的JavaDocs

https://docs.spring.io/spring-framework/docs/5.2.20.RELEASE/javadoc-api/org/springframework/test/util/ReflectionTestUtils.html#setField-java.lang.Class-java.lang.String-java.lang.Object-

Set the static field with the given name on the provided targetClass to the supplied value.

支持设置静态字段。

Answer 1

由于根据堆栈跟踪，java.lang.reflect.Field.set 抛出了 IllegalArgumentException，javadoc for Field.set具体原因可咨询。

它指出:

IllegalArgumentException - if the specified object is not an instance of the class or interface declaring the underlying field (or a subclass or implementor thereof), or if an unwrapping conversion fails.

比较您提供的 App 和 AppTest 类可以发现 AppTest 导入 org.apache.logging.log4j.core.Logger 而 App 导入 org.slf4j.Logger

由于您尝试注入(inject)记录器的模拟，因此请将 AppTest 中的第一个导入更改为 org.slf4j.logger。