ClassCastException throws in code has attempted to cast an object to a subclass of which it is not an instance.

• ClassCastException(): Constructs a ClassCastException with no detail message.
• ClassCastException( String s): Constructs a ClassCastException with specified detail message.

Exception Stack Trace

Caused by: java.lang.ClassCastException: org.apache.logging.slf4j.SLF4JLoggerContext cannot be cast to org.apache.logging.log4j.core.LoggerContext
    at org.apache.logging.log4j.core.LoggerContext.getContext(LoggerContext.java:190) ~[log4j-core-2.10.0.jar:2.10.0]
    at org.apache.logging.log4j.core.config.Configurator.setLevel(Configurator.java:291) ~[log4j-core-2.10.0.jar:2.10.0]
    at org.elasticsearch.common.logging.Loggers.setLevel(Loggers.java:149) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.common.logging.Loggers.setLevel(Loggers.java:144) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.index.SearchSlowLog.setLevel(SearchSlowLog.java:111) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.index.SearchSlowLog.(SearchSlowLog.java:106) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.index.IndexModule.(IndexModule.java:127) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.indices.IndicesService.createIndexService(IndicesService.java:440) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.indices.IndicesService.createIndex(IndicesService.java:413) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.cluster.metadata.MetaDataCreateIndexService$1.execute(MetaDataCreateIndexService.java:378) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.cluster.ClusterStateUpdateTask.execute(ClusterStateUpdateTask.java:45) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.cluster.service.ClusterService.executeTasks(ClusterService.java:634) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.cluster.service.ClusterService.calculateTaskOutputs(ClusterService.java:612) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.cluster.service.ClusterService.runTasks(ClusterService.java:571) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.cluster.service.ClusterService$ClusterServiceTaskBatcher.run(ClusterService.java:263) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.cluster.service.TaskBatcher.runIfNotProcessed(TaskBatcher.java:150) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.cluster.service.TaskBatcher$BatchedTask.run(TaskBatcher.java:188) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingRunnable.run(ThreadContext.java:575) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.runAndClean(PrioritizedEsThreadPoolExecutor.java:247) ~[elasticsearch-5.6.10.jar:5.6.10]
    at org.elasticsearch.common.util.concurrent.PrioritizedEsThreadPoolExecutor$TieBreakingPrioritizedRunnable.run(PrioritizedEsThreadPoolExecutor.java:210) ~[elasticsearch-5.6.10.jar:5.6.10]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) ~[na:1.8.0_151]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) ~[na:1.8.0_151]
    at java.lang.Thread.run(Unknown Source) ~[na:1.8.0_151]

Issue

This exception “org.apache.logging.slf4j.SLF4JLoggerContext cannot be cast to org.apache.logging.log4j.core.LoggerContext” occurs because project build with maven and contains spring-boot-starter-web which imports the dependency because we can’t skip with spring-boot-starter-web and need log4j.

Solutions 1

Solution to get log4j with web project is to exclude log4j-to-slf4 from class path as given below:

    
    org.springframework.boot
    spring-boot-starter-web
    
    
        org.apache.logging.log4j
        log4j-to-slf4j
    
    

Solutions 2

If you are using simple Spring boot console based application or any Spring template and interfacing with this exception.

org.springframework.boot
spring-boot-starter-log4j2



org.apache.logging.log4j
log4j-to-slf4j
2.0.2



org.apache.logging.log4j
log4j-to-slf4j;
2.0.2-sources;



org.apache.logging.log4j
log4j-slf4j-impl;
2.0.2;



org.apache.logging.log4j
log4j-slf4j-impl;
2.0.2-sources;

More Issues Solution

For more other JAVA/JDBC issues solution follow link JAVA/JDBC Issues.