Maven helps to manage the dependency of JARS . Most of the time it may happen that same JAR file with different versions is being loaded because some other jar files have it as dependency and thus causing the conflicts .

Typical example is have log4j or slf4j jar with different version in spring-xx.jar and junit-xxx.jar . So when you load you classes an conflict may arise and because of incompatible version of same jar file . For e.g.

<dependency>
	<groupId>org.springframework</groupId>
	<artifactId>spring-core</artifactId>
	<version>3.2.1.RELEASE</version>
</dependency>

The above jar uses log4j 1.2.17 (you can check the dependency using mvn dependency:tree).

Consider this log4j jar file is conflicting with some other higher version of log4j which is used by other jar. To resolve this issue we would have to remove the conflicting log4j jar from org.springframework.
it can be done as follows :

<dependency>
	<groupId>org.springframework</groupId>
	<artifactId>spring-core</artifactId>
	<version>3.2.1.RELEASE</version>
         <exclusions>
                <exclusion>
                    <groupId>log4j</groupId>
                    <artifactId>log4j</artifactId>
                </exclusion>
            </exclusions>
</dependency>

Cheers..

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