Java Runtime errors

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Core environment and runtime library

Documented:

Top patterns

  1. A class that is not available on the classpath or the class loader is closed

    java.lang.ClassNotFoundException is one of the most frequent exceptions in Java. It is a runtime error, however, it does not signal a bug in your application logic, but rather an issue with the environment (build system, dependency management, runtime environment, etc.)

    According to the javadoc, it "is thrown when an application tries to load in a class through its string name". There are several different situations leading to this error and you have to examine the stack trace thoroughly to be able to decide how to solve this problem.

    The first thing to check is whether you get this checked exception directly, or wrapped in a java.class.NoClassDefFoundException. The latter happens when the class not found was resolved during compilation time, but not found during runtime, which is a bit different than the first case and it needs special care. If this is what happened to you, then you should read that article (coming soon).

    Next we ask what is the class that was not found. Fortunately, in most cases, you can see it in the message of the exception. If this class was specified by you (either directly in the code, or via a configuration file), double check that you did not misspell it. Some practical advices:

    • Make sure you use the fully qualified name of the class (e.g. org.postgresql.ds.PGSimpleDataSource)
    • When loading a nested class, make sure you use the proper name (joined with a $ sign, e.g. test.MyClass$InnerClass).
    • If you are unsure, you can check the name of the class in the code by using MyClass.class.getName()

    If none of the above helped then you have an issue with your classpath, which requires some time and experience to resolve. When the java.lang.ClassNotFoundException is related to a third party library, you might want to ask for help in their support forums. However, if you want to debug it yourself, let me equip you with some theoretical and practical knowledge.

    • To understand what is class loading in Java, start with this StackOverflow question or the Java Language Specification §12.2. Roughly speaking, the classes that your application use are located in jar files on the file system. The classpath is a list of jar files which are searched through when your application loads a class. The java.lang.ClassNotFoundException means that the class you wanted to load is not present in any of the jar files on the classpath.
    • The configuration of your classpath depends on your runtime environment (i.e. do you run the application from console, from IDE, web container, etc), you can find more information on the specific forums. However, if you can use breakpoints to stop at specific points in your application, stop at the first line of java.net.URLClassLoader.findClass and check the value of the field ucp.
    • You should have an idea on which jar file contains the class that could not be loaded, and look for that jar in the classpath. If it is not there, you have to add that jar to the classpath (precise details depend on the runtime environment).
    • If you find the jar you suspect to contain your class, check if it is true by opening the jar file (they are simple zip files actually) and look for the class definition in the directory structure in it (the directory structure must be identical to the package structure of the java code). At this point you should realize that the class is not present, otherwise the problem would have been found previously during debugging.
    • There are two reasons for class not being present in the jar: the first is that you have an incorrect version of the library you wanted to use. To fix this, you have to tweak your build system (maven, ant, sbt, gradle etc) by making sure that you configured the right version of the library as the dependency, and that you don’t have conflicting library versions. To find out how to do this, look for help on the forums of that build system.
    • The other reason of the class not being present is that it’s a bug in that library. If this is a third-party library, you might want to check the support forum and the release notes. If this library was written by you, then try to rebuild this library and check if the class you look for is present in the resulting jar file.
  2. ClassLoader.loadClass() has thrown a ClassNotFoundException
    No solution
  3. The class could not be found

    This error pattern looks similar to error pattern 88439.

    However, in this case, we are sure that this happens when sun.misc.URLClassPath.getResource(String name, boolean check) returns null. Practically every exception that happens in getResource is handled by returning null.


DescriptionException TypeEntry MethodWeb pages
NamingExceptionInitialContext.lookup43
NamingExceptionInitialContext.lookup34
NamingExceptionInitialContext.lookup27
NamingExceptionInitialContext.lookup25
NamingExceptionInitialContext.lookup24
NamingExceptionInitialContext.lookup24
NamingExceptionInitialContext.lookup24
NamingExceptionInitialContext.lookup18
NamingExceptionInitialContext.lookup16
NamingExceptionInitialContext.lookup16
NamingExceptionInitialContext.lookup14
NamingExceptionInitialContext.lookup14
NamingExceptionInitialContext.lookup13
NamingExceptionInitialContext.lookup13
NamingExceptionInitialContext.lookup12
NamingExceptionInitialContext.lookup12
NamingExceptionInitialContext.lookup11
NamingExceptionInitialContext.lookup10
NamingExceptionInitialContext.lookup9
NamingExceptionInitialContext.lookup9
NamingExceptionInitialContext.lookup9
NamingExceptionInitialContext.lookup9
NamingExceptionInitialContext.lookup9
NamingExceptionInitialContext.lookup9
NamingExceptionInitialContext.lookup8
NamingExceptionInitialContext.lookup8
NamingExceptionInitialContext.lookup8
NamingExceptionInitialContext.lookup8
NamingExceptionInitialContext.lookup7
NamingExceptionInitialContext.lookup7
NamingExceptionInitialContext.lookup6
NamingExceptionInitialContext.lookup6
NamingExceptionInitialContext.lookup5
NamingExceptionInitialContext.lookup5
NamingExceptionInitialContext.lookup5
NamingExceptionInitialContext.lookup5
NamingExceptionInitialContext.lookup5
NamingExceptionInitialContext.lookup5
NamingExceptionInitialContext.lookup5
NamingExceptionInitialContext.lookup5
NamingExceptionInitialContext.lookup4
NamingExceptionInitialContext.lookup4
NamingExceptionInitialContext.lookup4
NamingExceptionInitialContext.lookup4
NamingExceptionInitialContext.lookup4
NamingExceptionInitialContext.lookup4
NamingExceptionInitialContext.lookup4
NamingExceptionInitialContext.lookup4
NamingExceptionInitialContext.lookup4
NamingExceptionInitialContext.lookup4
Package nameClass namePatterns foundSolution coverageDescription coverage
javax.namingInitialContext1069
javax.namingNameImpl4
javax.namingCompositeName3
javax.namingReference2
javax.namingNamingException1
javax.namingNameNotFoundException1
Package nameClass nameMethod namePatterns foundSolution coverage
javax.namingInitialContextlookup601
javax.namingInitialContext<init>248
javax.namingInitialContextinit125
javax.namingInitialContextgetDefaultInitCtx33
javax.namingInitialContextbind18
javax.namingInitialContextrebind12
javax.namingInitialContextgetURLOrDefaultInitCtx8
javax.namingInitialContextgetNameParser4
javax.namingInitialContextlistBindings3
javax.namingInitialContextcreateSubcontext3
javax.namingInitialContextrename2
javax.namingInitialContextunbind2
javax.namingInitialContextlist2
javax.namingInitialContextdoLookup2
javax.namingInitialContextinternalInit1
javax.namingInitialContextaddToEnvironment1
javax.namingInitialContextgetEnvironment1
javax.namingInitialContextgetNameInNamespace1
javax.namingInitialContextclose1
javax.namingInitialContextgetURLScheme1
Package nameClass nameMethod nameException TypePatterns foundSolution coverage
javax.namingInitialContextlookupNameNotFoundException175
javax.namingInitialContextlookupNamingException119
javax.namingInitialContextlookupCommunicationException48
javax.namingInitialContextlookupNoClassDefFoundError19
javax.namingInitialContextlookupCOMM_FAILURE17
javax.namingInitialContextlookupCannotInstantiateObjectException15
javax.namingInitialContextlookupClassNotFoundException14
javax.namingInitialContextlookupConnectException11
javax.namingInitialContextlookupNullPointerException10
javax.namingInitialContextlookupNotFound9
javax.namingInitialContextlookupException9
javax.namingInitialContextlookupAuthenticationException9
javax.namingInitialContextlookupMARSHAL8
javax.namingInitialContextlookupNoInitialContextException8
javax.namingInitialContextlookupServiceUnavailableException8
javax.namingInitialContextlookupConfigurationException7
javax.namingInitialContextlookupSecurityException6
javax.namingInitialContextlookupClassCastException5
javax.namingInitialContextlookupAccessControlException4
javax.namingInitialContextlookupIllegalArgumentException4
javax.namingInitialContextlookupConnectIOException3
javax.namingInitialContextlookupLinkException3
javax.namingInitialContextlookupNotContextException3
javax.namingInitialContextlookupInvalidClassException3
javax.namingInitialContextlookupPoolingException3
javax.namingInitialContextlookupIOException3
javax.namingInitialContextlookupNoPermissionException3
javax.namingInitialContextlookupConnectorRuntimeException3
javax.namingInitialContextlookupConnectException2
javax.namingInitialContextlookupINITIALIZE2
javax.namingInitialContextlookupinitial2
javax.namingInitialContextlookupRemoteException2
javax.namingInitialContextlookupInvalidObjectException2
javax.namingInitialContextlookupRuntimeException2
javax.namingInitialContextlookupUnsatisfiedLinkError2
javax.namingInitialContextlookupUnmarshalException2
javax.namingInitialContextlookupUnknownException2
javax.namingInitialContextlookupInvocationTargetException2
javax.namingInitialContextlookupUnknownHostException2
javax.namingInitialContextlookupIllegalStateException2
javax.namingInitialContextlookupAssertionError2
javax.namingInitialContextlookupStackOverflowError2
javax.namingInitialContextlookupEOFException2
javax.namingInitialContextlookupFileNotFoundException2
javax.namingInitialContextlookupOBJECT_NOT_EXIST2
javax.namingInitialContextlookupjava2
javax.namingInitialContextlookupNoSuchFieldError2
javax.namingInitialContextlookupCannotProceed1
javax.namingInitialContextlookupNotSerializableException1
javax.namingInitialContextlookupjava1