我正在制作一个支持多个版本 API 的 API 包装器库。最近的 API 版本中添加了一个公共类。我正在尝试针对最新的 API 版本编译包装器，并在运行时检查新类是否存在。我试图避免反射，而是捕捉
NoClassDefFoundError它一直有效，直到我添加一个返回不存在的类extends的类的方法。然后我的库无法加载。我的意思是：
BaseClassChildClassChildClassBaseClassObject标准的哪一部分描述了这种行为？
这是一个最小的例子：
public class TestLoading {
public static void main(String[] args) throws Exception {
Class.forName(BaseClass.class.getName());
// Class.forName(B.class.getName())
URL classFileB =
TestLoading.class.getResource(TestLoading.class.getSimpleName() + "$ChildClass.class");
if (classFileB != null) {
if (!"file".equals(classFileB.getProtocol())) {
throw new UnsupportedOperationException();
}
Path path = new File(classFileB.getPath()).toPath();
System.out.println("deleting: " + path);
Files.delete(path);
}
loadMyClass(ObjectReturner.class.getName());
loadMyClass(BaseClassReturner.class.getName());
}
private static void loadMyClass(String name) throws ClassNotFoundException {
System.out.println("loading: " + name + "...");
try {
Class.forName(name);
} catch (Throwable e) {
e.printStackTrace(System.out);
}
}
public static class BaseClass {
static {
System.out.println("loaded: " + BaseClass.class.getName());
}
}
public static class ChildClass extends BaseClass {
static {
System.out.println("loaded: " + ChildClass.class.getName());
}
}
public static class ObjectReturner {
static {
System.out.println("loaded: " + ObjectReturner.class.getName());
}
public Object getObject() {
return new ChildClass();
}
}
public static class BaseClassReturner {
static {
System.out.println("loaded: " + BaseClassReturner.class.getName());
}
public BaseClass getObject() {
if ("".length() == 10) {
return new ChildClass();
} else {
return null;
}
}
}
}
程序输出
loaded: snippet.TestLoading$BaseClass
deleting: C:\keep\eclipse\formendix\_pasted_code_\target\classes\snippet\TestLoading$ChildClass.class
loading: snippet.TestLoading$ObjectReturner...
loaded: snippet.TestLoading$ObjectReturner
loading: snippet.TestLoading$BaseClassReturner...
java.lang.NoClassDefFoundError: snippet/TestLoading$ChildClass
at java.base/java.lang.Class.forName0(Native Method)
at java.base/java.lang.Class.forName(Class.java:377)
at snippet.TestLoading.loadMyClass(TestLoading.java:31)
at snippet.TestLoading.main(TestLoading.java:25)
Caused by: java.lang.ClassNotFoundException: snippet.TestLoading$ChildClass
at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:606)
at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:168)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:522)
... 4 more
我已经使用
-Xlog:class+initloading: com.olympus.trade.util.TestLoading$ObjectReturner...
[0.434s][info][class,init] Start class verification for: com.olympus.trade.util.TestLoading$ObjectReturner
[0.434s][info][class,init] 737 Initializing 'java/util/AbstractSequentialList'(no method) (0x000000080009a570)
[0.434s][info][class,init] End class verification for: com.olympus.trade.util.TestLoading$ObjectReturner
[0.434s][info][class,init] 738 Initializing 'java/util/LinkedList'(no method) (0x000000080009aa40)
[0.434s][info][class,init] 739 Initializing 'com/olympus/trade/util/TestLoading$ObjectReturner' (0x0000000800067450)
loaded: com.olympus.trade.util.TestLoading$ObjectReturner
[0.434s][info][class,init] 740 Initializing 'java/util/LinkedList$Node'(no method) (0x000000080009b1b0)
[0.435s][info][class,init] 741 Initializing 'sun/util/locale/provider/LocaleProviderAdapter' (0x000000080009b3c0)
[0.435s][info][class,init] 742 Initializing 'sun/util/locale/provider/LocaleProviderAdapter$Type' (0x000000080009b658)
[0.435s][info][class,init] 743 Initializing 'java/util/Collections$UnmodifiableList'(no method) (0x000000080009ba80)
loading: com.olympus.trade.util.TestLoading$BaseClassReturner...[0.435s][info][class,init] 744 Initializing 'java/util/Collections$UnmodifiableRandomAccessList'(no method) (0x000000080009bf50)
[0.435s][info][class,init] Start class verification for: com.olympus.trade.util.TestLoading$BaseClassReturner
[0.436s][info][class,init] 745 Initializing 'sun/util/locale/provider/JRELocaleProviderAdapter'(no method) (0x000000080009c620)
[0.436s][info][class,init] 746 Initializing 'java/lang/ReflectiveOperationException'(no method) (0x0000000800004028)
[0.436s][info][class,init] 747 Initializing 'sun/util/locale/provider/FallbackLocaleProviderAdapter' (0x000000080009c900)
[0.436s][info][class,init] 748 Initializing 'java/lang/ClassNotFoundException'(no method) (0x0000000800004288)
[0.436s][info][class,init] 749 Initializing 'java/lang/LinkageError'(no method) (0x00000008000044f8)
[0.436s][info][class,init] 750 Initializing 'java/lang/NoClassDefFoundError'(no method) (0x0000000800004758)
[0.436s][info][class,init] Verification for com.olympus.trade.util.TestLoading$BaseClassReturner has exception pending 'java.lang.NoClassDefFoundError com/olympus/trade/util/TestLoading$ChildClass'
[0.436s][info][class,init] End class verification for: com.olympus.trade.util.TestLoading$BaseClassReturner
[0.436s][info][class,init] 751 Initializing 'java/lang/Throwable$PrintStreamOrWriter'(no method) (0x000000080009cec0)
[0.436s][info][class,init] 752 Initializing 'java/lang/Throwable$WrappedPrintStream'(no method) (0x000000080009d0d8)
[0.436s][info][class,init] 753 Initializing 'sun/util/locale/LanguageTag' (0x000000080009d308)
java.lang.NoClassDefFoundError: com/olympus/trade/util/TestLoading$ChildClass[0.436s][info][class,init] 754 Initializing 'java/util/Collections$EmptyIterator' (0x000000080009d550)
您的代码在
BaseClassReturner.class.getName()BaseClassReturner.classBaseClassReturner.class[268.399s][info][class,init] Start class verification for: com.olympus.trade.util.TestLoading$BaseClassReturner
[268.401s][info][class,init] Verification for com.olympus.trade.util.TestLoading$BaseClassReturner has exception pending 'java.lang.NoClassDefFoundError com/olympus/trade/util/TestLoading$ChildClass'
[268.401s][info][class,init] End class verification for: com.olympus.trade.util.TestLoading$BaseClassReturner
JVM 在返回其实例之前开始验证该类，但它显然失败了，因为它在其主体中引用了
ChildClass