我收到“java.lang.ClassNotFoundException: com.google.gson.Gson”错误，即使它是在我的类路径中定义的

Question

I'm trying to parse some JSON object strings that I'm getting using gson-1.6.jar I have placed it in the same location as my other .jars and have added it to my buildpath in eclipse.

The other libraries worked fine when I added them and I can use them without any issues, but when I try to create the JSON object, I get the titular error. I've looked through the other questions with this error, but I couldn't find a solution that didn't involve something that I've tried or something unrelated.

I import it near the top using:

import com.google.gson.Gson;

Then use it later in a static function like so:

Gson g = new Gson();

Here is my eclipse generated classpath file [Path] substituted for actual path:

<?xml version="1.0" encoding="UTF-8"?>
<classpath>
    <classpathentry kind="src" path="src"/>
    <classpathentry kind="con" path="org.eclipse.jdt.launching.JRE_CONTAINER/org.eclipse.jdt.internal.debug.ui.launcher.StandardVMType/jre6">
        <attributes>
            <attribute name="owner.project.facets" value="java"/>
        </attributes>
    </classpathentry>
    <classpathentry kind="con" path="org.eclipse.jst.server.core.container/org.eclipse.jst.server.tomcat.runtimeTarget/Apache Tomcat v5.5">
        <attributes>
            <attribute name="owner.project.facets" value="jst.web"/>
        </attributes>
    </classpathentry>
    <classpathentry kind="con" path="org.eclipse.jst.j2ee.internal.web.container"/>
    <classpathentry kind="con" path="org.eclipse.jst.j2ee.internal.module.container"/>
    <classpathentry kind="lib" path="[Path]/jabbabase-ws-jwsdp-client-2.4.7.jar"/>
    <classpathentry kind="lib" path="[Path]/log4j-1.2.16.jar"/>
    <classpathentry kind="lib" path="[Path]/gson-1.6.jar"/>
    <classpathentry kind="output" path="build/classes"/>
</classpath>

as well as my build path window:

I'm a little lost at this point. I've tried Google and the posts basically just say to add to your build path. Anybody have any ideas?

Edit: More Info

The code referencing com.google.gson.GSON is used as a bean by a jsp. This function is called from the jsp and the error occurs as soon as the function is executed. The first line in the function is:

Gson g = new Gson();

It seems to compile and deploy fine, but when it is executed, I get the error message.

Thanks

Answer 1

In case of a JSP/Servlet webapplication, you just need to drop 3rd party JAR files in /WEB-INF/lib folder. If the project is a Dynamic Web Project , then Eclipse will automatically take care about setting the buildpath right as well. You do not need to fiddle with Eclipse buildpath. Don't forget to undo it all.

Answer 2

I faced same problem and tried above solutions but none of them worked for me. Then I tried following steps and the problem was solved:

• Go to the project properties.
• Go to Java Build Path option.
• Then add *.jar file as external jar.
• Then go to the order and export option and select the libraries and jars of the project.
• save the current changes and clean the project and run the project again.

Answer 3

Click on Deployment Assembly ( right above Java Build Path that you show as active ) and make sure that you see json-lib-2.4-jdk15.jar there.

Usually, you should add it to your build path and export it from your project. Once it's exported you will see the WTP warning that it's not a part of the deployment. Choose the Quick Fix option and add it to your deployment path.

Answer 4

I was just having the same issue...

To resolve the problem (at least in my case) ensure you have included the lib folder in your bundle classpath:

Manifest-Version: 1.0
... 
Bundle-ClassPath: lib/gson-1.6.jar,
 .
...

Or if you want to include all jar's in the folder:

Bundle-ClassPath: lib/

You will still need to place the jar files on the java build path as shown above. Then your imported jar's should appear in the folder "Referenced Libraries"

Answer 5

Well for me the problem got resolved by adding the jars in my APACHE/TOMCAT/lib folder ! .

Answer 6

I had the same problem when developing a KNIME Node/plugin in the Eclipse environment. The solution was not only to add the gson.jar as an externar JAR to the build path, it was also required to go to plugin.xml , then the Dependencies tab and add com.google.gson as a required plugin.

Answer 7

Do the Quick fix in the Markers tab.

Reference: https://metamug.com/blog/eclipse-gson-class-not-found

Answer 8

I ran into the above error when building and running inside Eclipse, where everything seemed to be fine, with the exception of this error. However, I discovered that a Maven build failed and that I needed to include Gson in my pom.xml. After fixing the pom.xml, everything fell into place.

Answer 9

you can include maven dependency like below in your pom.xml file

<!-- https://mvnrepository.com/artifact/com.google.code.gson/gson --> <dependency> <groupId>com.google.code.gson</groupId> <artifactId>gson</artifactId> <version>2.8.6</version> </dependency>

Answer 10

In case it helps anyone troubleshoot as I just wasted 30 minutes on this in Eclipse as a first time user - I had added the Gson jar to the 'ModulePath' section of build path libraries (alongside JRE system library). I needed to add it to the 'Classpath' to resolve this error.