java.lang.NoClassDefFoundError: 无法初始化类 | 静态块

Question

I'm stuck with a strange issue where my JVM is throwing java.lang.NoClassDefFoundError. Any help in identifying the problem is greatly appreciated.

public class AccessorFactory
{
private static Map classMap = null;
    static
    {
        classMap = new HashMap(100);
        classMap.put("bills", Class.forName("com.example.BillAccessor"));
    }
}

public class BillAccessor
{
    class BillInnerClass
    {
        //some code
    }
}

I have 3 classes AccessorFactory.class, BillAccessor.class and BillAccessor$BillInnerClass.class. All 3 are in same jar file and all are present in the classpath.

I've recently changed something in BillAccessor$BillInnerClass class and replaced this file in the jar file and restarted application instance in server (jboss).

Post restart I'm getting

java.lang.NoClassDefFoundError: Could not initialize class AccessorFactory

AccessorFactory class present in the jar file and in the class path. Nothing else is changed except that I've replaced BillAccessor$BillInnerClass.

Answer 1

NoClassDefFoundError typically means the JVM has located the class (as opposed to ClassNotFoundException ), but unable to load it because of not having some dependent classes.

Not sure if you tried rebuilding the entire jar (with all 3 classes) and use the new jar in JBoss?

Answer 2

This is an old question, but I think it deserves a better answer.

There are actually two things going on here.

1. Some time before the exception that the Question is talking about, the JVM has attempted to execute the static initialization for the AccessorFactory class. That has thrown an unchecked exception, causing initialization to fail. As a result of that, the AccessorFactory class has been marked as failed. It is effectively dead. The JVM will never retry the initialization.

2. The exception you are seeing is an NoClassDefFoundError . This has occurred because ¹ the JVM has tried to load or initialize another class that depends on AccessorFactory . The JVM has noted that AccessorFactory has been marked as failed, and thrown this exception.

So what caused the original problem?

Unfortunately, we can't say. There is insufficient information ² . The code in the static initializer is:

    classMap = new HashMap(100);
    classMap.put("bills", Class.forName("com.example.BillAccessor"));

It is highly unlikely that the first statement failed, but the second one is attempting to load a class. That could fail for a number of reasons, including the following.

• It could fail to find the class at all. That would result in a ClassNotFoundException .

• It could detect a fault in a .class file being loaded, that would result in an Error of some kind.

• It could detect a binary version incompatibility between a .class file being loaded and some other class that has already been loaded. This are a range of things that could cause this, but they will also result in an Error of some kind.

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^{1 - The exception can happen for other reasons too, but in this case the exception's message tells us it is an earlier class initialization failure.
2 - The real reason was most likely reported in an earlier stacktrace which could be earlier in the OP's log file.}

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Having said that, I don't think that the code in the question is "real". Specifically, the static as shown should not compile . The ClassNotFoundException thrown by forName is a checked exception and it must be caught. The JLS does not allow checked exceptions to propagate from a static block.