java.lang.NoClassDefFoundError: com/google/gson/Gson

Question

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>activemq.apache</groupId>
    <artifactId>graduation03</artifactId>
    <version>1.0-SNAPSHOT</version>

    <dependencies>

        <!-- webSocket -->
        <dependency>
            <groupId>javax</groupId>
            <artifactId>javaee-api</artifactId>
            <version>7.0</version>
        </dependency>


        <!-- MySql 5.5 Connector -->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.45</version>
        </dependency>

        <!-- config -->
        <dependency>
            <groupId>com.typesafe</groupId>
            <artifactId>config</artifactId>
        </dependency>
        <dependency>
            <groupId>com.github.racc</groupId>
            <artifactId>typesafeconfig-guice</artifactId>
        </dependency>

        <dependency>
            <groupId>org.fusesource.stompjms</groupId>
            <artifactId>stompjms-client</artifactId>
            <version>1.18</version>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.31</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/javax.servlet/javax.servlet-api -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/jstl/jstl -->
        <dependency>
            <groupId>jstl</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>

        <dependency>
            <groupId>com.google.code.gson</groupId>
            <artifactId>gson</artifactId>
            <version>2.3.1</version>
        </dependency>

    </dependencies>

</project>

Answer 1

看最后一个报错，ClassNotFoundException，找不到包。

可能是你修改了 pom.xml 并没有令其生效，那么右击项目 -> maven -> update..

Answer 2

或者可以看下你的本地库里有没有对应的jar

Answer 3

如果是eclipse可能会出现这个问题，idea你修改pom文件是会提醒你更新的。
建议在命令行下重新构建项目，如果是eclipse 建议使用maven插件构建eclipse配置文件。

mvn clean install 
mvn eclipse:eclipse

Answer 4

检查一下有没有gson.jar这个包？