Jacoco与Mockito集成报NoClassDefFoundError，如何正常测并生成覆盖率报告？

我有一个使用jacoco-maven-plugin、maven-surefire-plugin和Mockito的项目，配置如下：

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-surefire-plugin</artifactId>
</plugin>
<plugin>
    <groupId>org.jacoco</groupId>
    <artifactId>jacoco-maven-plugin</artifactId>
    <version>${jacoco-maven-plugin.version}</version>
    <executions>
        <execution>
            <id>prepare-agent</id>
            <goals>
                <goal>prepare-agent</goal>
            </goals>
        </execution>
        <execution>
            <id>report</id>
            <phase>prepare-package</phase>
            <goals>
                <goal>report</goal>
            </goals>
        </execution>
    </executions>
</plugin>

运行测试时出现如下错误：

java.lang.NoClassDefFoundError: com.foo.Foo$MockitoMock$yT0N0ogW (initialization failure)
        at java.base/java.lang.J9VMInternals.initializationAlreadyFailed(J9VMInternals.java:156) ~[na:na]
        at java.base/jdk.internal.misc.Unsafe.allocateInstance(Native Method) ~[na:na]
        at jdk.unsupported/sun.misc.Unsafe.allocateInstance(Unsafe.java:864) ~[na:na]
        at org.objenesis.instantiator.sun.UnsafeFactoryInstantiator.newInstance(UnsafeFactoryInstantiator.java:47) ~[objenesis-3.3.jar:3.3]
        at org.objenesis.ObjenesisBase.newInstance(ObjenesisBase.java:73) ~[objenesis-3.3.jar:3.3]
        at org.mockito.internal.creation.instance.ObjenesisInstantiator.newInstance(ObjenesisInstantiator.java:22) ~[mockito-core-5.3.1.jar:na]
        at org.mockito.internal.creation.bytebuddy.InlineDelegateByteBuddyMockMaker.doCreateMock(InlineDelegateByteBuddyMockMaker.java:376) ~[mockito-core-5.3.1.jar:na]
        at org.mockito.internal.creation.bytebuddy.InlineDelegateByteBuddyMockMaker.createMock(InlineDelegateByteBuddyMockMaker.java:334) ~[mockito-core-5.3.1.jar:na]
        at org.mockito.internal.creation.bytebuddy.InlineByteBuddyMockMaker.createMock(InlineByteBuddyMockMaker.java:56) ~[mockito-core-5.3.1.jar:na]
        at org.mockito.internal.util.MockUtil.createMock(MockUtil.java:99) ~[mockito-core-5.3.1.jar:na]
        at org.mockito.internal.MockitoCore.mock(MockitoCore.java:88) ~[mockito-core-5.3.1.jar:na]
        at org.mockito.Mockito.mock(Mockito.java:2101) ~[mockito-core-5.3.1.jar:na]
        at org.springframework.boot.test.mock.mockito.SpyDefinition.createSpy(SpyDefinition.java:116) ~[spring-boot-test-3.1.1.jar:3.1.1]
        at org.springframework.boot.test.mock.mockito.MockitoPostProcessor.createSpyIfNecessary(MockitoPostProcessor.java:331) ~[spring-boot-test-3.1.1.jar:3.1.1]
        at org.springframework.boot.test.mock.mockito.MockitoPostProcessor$SpyPostProcessor.postProcessAfterInitialization(MockitoPostProcessor.java:465) ~[spring-boot-test-3.1.1.jar:3.1.1]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(AbstractAutowireCapableBeanFactory.java:434) ~[spring-beans-6.0.10.jar:6.0.10]
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.postProcessObjectFromFactoryBean(AbstractAutowireCapableBeanFactory.java:1885) ~[spring-beans-6.0.10.jar:6.0.10]
        at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:105) ~[spring-beans-6.0.10.jar:6.0.10]
        ... 121 common frames omitted
Caused by: java.lang.NullPointerException: null
        at java.base/java.util.ArrayList.add(ArrayList.java:453) ~[na:na]
        at java.base/java.util.ArrayList.add(ArrayList.java:467) ~[na:na]
        at java.base/java.lang.invoke.MethodTypeHelper.parseIntoClass(MethodTypeHelper.java:237) ~[na:na]
        at java.base/java.lang.invoke.MethodHandleResolver.fromFieldDescriptorString(MethodHandleResolver.java:306) ~[na:na]
        at java.base/java.lang.invoke.MethodHandleResolver.resolveConstantDynamic(MethodHandleResolver.java:102) ~[na:na]
        at com.foo.Foo$MockitoMock$yT0N0ogW.<clinit>(Unknown Source) ~[classes/:na]
        at java.base/jdk.internal.misc.Unsafe.allocateInstance(Native Method) ~[na:na]
        at java.base/java.lang.invoke.DirectMethodHandle.allocateInstance(DirectMethodHandle.java:520) ~[na:na]
        at java.base/java.lang.invoke.MethodHandle.invokeWithArguments(MethodHandle.java:732) ~[na:na]
        at org.mockito.internal.util.reflection.InstrumentationMemberAccessor$Dispatcher$ByteBuddy$vQ02mWmG.invokeWithArguments(Unknown Source) ~[na:na]
        at org.mockito.internal.util.reflection.InstrumentationMemberAccessor.lambda$newInstance$0(InstrumentationMemberAccessor.java:199) ~[mockito-core-5.3.1.jar:na]
        at org.mockito.internal.creation.bytebuddy.InlineDelegateByteBuddyMockMaker.lambda$newInstance$4(InlineDelegateByteBuddyMockMaker.java:636) ~[mockito-core-5.3.1.jar:na]
        at org.mockito.internal.util.reflection.InstrumentationMemberAccessor.newInstance(InstrumentationMemberAccessor.java:188) ~[mockito-core-5.3.1.jar:na]
        at org.mockito.internal.util.reflection.ModuleMemberAccessor.newInstance(ModuleMemberAccessor.java:49) ~[mockito-core-5.3.1.jar:na]
        at org.mockito.internal.creation.bytebuddy.InlineDelegateByteBuddyMockMaker.newInstance(InlineDelegateByteBuddyMockMaker.java:631) ~[mockito-core-5.3.1.jar:na]
        at org.mockito.internal.creation.bytebuddy.InlineDelegateByteBuddyMockMaker.doCreateMock(InlineDelegateByteBuddyMockMaker.java:369) ~[mockito-core-5.3.1.jar:na]
        ... 132 common frames omitted

尝试在surefire插件配置中添加<argLine>...</argLine>后，测试可正常运行，但无法生成jacoco.exec文件及Jacoco覆盖率报告。请问该错误产生的原因是什么？如何才能让测试正常运行同时生成Jacoco覆盖率报告？

错误原因 #

这个错误是Jacoco的prepare-agent目标注入的JVM参数与Mockito默认的内联模拟机制冲突导致的：

• Jacoco的prepare-agent会自动给surefire插件设置argLine参数，加入覆盖率采集的JVM代理（-javaagent:jacocoagent.jar）
• Mockito 5+默认启用内联模拟（Inline Mock Maker），这种机制会动态生成字节码创建模拟类。Jacoco代理在处理这些动态生成的Mockito模拟类时，会触发JVM内部的空指针异常，导致模拟类初始化失败，最终抛出NoClassDefFoundError。

手动配置surefire的argLine时，会覆盖Jacoco自动注入的代理参数，导致Jacoco无法采集覆盖率数据，所以测试能正常运行，但生成不了报告。

解决方法 #

方法一：保留Jacoco参数，不覆盖argLine #

修改surefire插件配置，引用Jacoco生成的argLine变量，同时添加自定义参数（如果需要）：

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-surefire-plugin</artifactId>
    <configuration>
        <!-- 引用Jacoco注入的参数，避免覆盖，可追加自定义JVM参数 -->
        <argLine>${argLine}</argLine>
        <!-- 显式指定Jacoco输出文件路径，确保生成位置正确 -->
        <systemPropertyVariables>
            <jacoco-agent.destfile>${project.build.directory}/jacoco.exec</jacoco-agent.destfile>
        </systemPropertyVariables>
    </configuration>
</plugin>

这样既保留了Jacoco的覆盖率采集代理，又不会产生冲突，测试和报告生成都能正常工作。

方法二：切换Mockito模拟生成方式（备选） #

如果方法一无效，可以强制Mockito使用子类模拟（Subclass Mock Maker），避免与Jacoco的字节码修改冲突：

1. 在src/test/resources/mockito-extensions/目录下创建文件org.mockito.plugins.MockMaker，内容为：

mock-maker-subclass

2. 或者通过JVM参数指定：

<argLine>${argLine} -Dmockito.mock-maker=subclass</argLine>

注意：这种方式会限制Mockito的功能（比如无法模拟final类、静态方法、私有方法等），仅作为备选方案。

方法三：确保版本兼容 #

使用Jacoco 0.8.8及以上版本，它对Mockito 5+的兼容性更好，建议升级Jacoco插件到最新稳定版。

验证结果 #

执行Maven命令：

mvn clean test jacoco:report

测试正常运行后，会在target目录下生成jacoco.exec文件，HTML格式的覆盖率报告位于target/site/jacoco目录下。

内容的提问来源于stack exchange，提问作者NickNgn