Solve the problem that cannot be cast to javax. servlet. Filter reports an error. javax. servlet. filter

Solve the problem that cannot be cast to javax. servlet. Filter reports an error. javax. servlet. filter

Cannot be cast to javax. servlet. Filter error due to servlet-api.jar conflict

When you use maven to develop a web application, an error is reported during startup:

Jar not loaded. See Servlet Spec 2.3, section 9.7.2. Offending class: javax/servlet/Servlet. class

Then an error is output:

Severe: Exception starting filter encodingFilterjava. lang. ClassCastException: org. springframework. web. filter. CharacterEncodingFilter cannot be cast to javax. servlet. Filter

The cause is that after tomcat is started, all the jar packages in the tomcat/lib directory are read into the memory, if the WEB-INF/lib directory in the application in the webapps directory has the same package, it will not be loaded,

Similar problems may occur between packages of different versions.

The solution to this problem is to use the <scope> label for the servlet-ap.jar, servlet-api and jsp-api are used during compilation, but these two dependencies are not needed during packaging.

As follows:

<dependency> <groupId>javax.servlet</groupId> <artifactId>servlet-api</artifactId> <version>2.4</version> <scope>provided</scope></dependency>

<Dependency> <scope>, which mainly manages the deployment of dependencies. Currently, <scope> can use five values:

* Compile, default value, applicable to all stages and will be released along with the project.
* Provided, similar to compile, expects JDK, container, or user to provide this dependency. For example, servlet. jar.
* Runtime, used only at runtime, such as the JDBC driver, applicable to the running and testing stages.
* Test, which is only used for testing and is used to compile and run the test code. Will not be released along with the project.
* System, similar to provided, must explicitly provide jar containing dependencies. Maven will not find it in Repository.

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