java.lang.ClassCastException：org.apache.camel.builder.ValueBuilder无法转换为java.lang.String

Question

I am getting crazy because I am not able to track down why I have this exception in my camel route:

java.lang.ClassCastException: org.apache.camel.builder.ValueBuilder
cannot be  cast to java.lang.String

Can you please give me an hint of what does it mean? I have no explicit casts in my code.

After seeing your (correct) annotations I add:

1. I cannot reproduce the exception in a few lines of code because in this case I was able to solve it on my own
2. I know what a classcast exception is but infact I never assign a valuebuilder to a string variable or cast a string
3. I tried to debug and trace but the same piece of code that now works tomorrow launches this exception
4. I have read camel documentation but probably I still do not understand what a ValueBuilder is for

Can you suggest me a better way to debug exceptions with eclipse debugger?

I can finally add the exception WITH stacktrace:

java.lang.ClassCastException
org.apache.camel.builder.ValueBuilder cannot be cast to java.lang.String
at org.apache.camel.component.cache.CacheProducer.process(CacheProducer.java:61)       
at org.apache.camel.util.AsyncProcessorConverterHelper$ProcessorToAsyncProcessorBridge.  process(AsyncProcessorConverterHelper.java:61)
at org.apache.camel.util.AsyncProcessorHelper.process(AsyncProcessorHelper.java:73)
at org.apache.camel.processor.SendProcessor$2.doInAsyncProducer(SendProcessor.java:122)
at org.apache.camel.impl.ProducerCache.doInAsyncProducer(ProducerCache.java:298)
at org.apache.camel.processor.SendProcessor.process(SendProcessor.java:117)
at org.apache.camel.util.AsyncProcessorHelper.process(AsyncProcessorHelper.java:73)
at org.apache.camel.processor.DelegateAsyncProcessor. processNext(DelegateAsyncProcessor.java:99)
at org.apache.camel.processor.DelegateAsyncProcessor.process(DelegateAsyncProcessor.java:90)
at org.apache.camel.management.InstrumentationProcessor. process(InstrumentationProcessor.java:72)

Thanks, Mario

Answer 1

From the API Specifications for the ClassCastException :

Thrown to indicate that the code has attempted to cast an object to a subclass of which it is not an instance.

So, for example, when you try to assign a org.apache.camel.builder.ValueBuilder to a java.lang.String , the operation fails to be accomplished because java.lang.String is not an subclass of org.apache.camel.builder.ValueBuilder , and therefore a ClassCastException is thrown.

Answer 2

I have found the problem!

This is the previous code (that worked), taken from official camel tutorial:

in.setHeader(CacheConstants.CACHE_OPERATION, constant(CacheConstants.CACHE_OPERATION_ADD));

This is the correct code that produces no exception:

in.setHeader(CacheConstants.CACHE_OPERATION, CacheConstants.CACHE_OPERATION_ADD);

constant() changes a String in a ValueBuilder causing the exception.

I suppose this is a bug because the behaviour of camel cache component has changed.

Mario