【排错】springboot项目，启动报An attempt was made to call the method com.google.gson.GsonBuilder.setLenient()Lcom/google/gson/GsonBuilder; but it does not exist.

pom文件新引入：

    <dependency>
        <groupId>com.google.code.gson</groupId>
        <artifactId>gson</artifactId>
        <version>2.3</version>
    </dependency>


但启动后报错：

An attempt was made to call the method com.google.gson.GsonBuilder.setLenient()Lcom/google/gson/GsonBuilder; but it does not exist. Its class, com.google.gson.GsonBuilder, is available from the following locations:

    jar:file:/home/haoyun/apache-tomcat-8.5.40/webapps/admin/WEB-INF/lib/gson-2.3.1.jar!/com/google/gson/GsonBuilder.class

It was loaded from the following location:

    file:/home/haoyun/apache-tomcat-8.5.40/webapps/admin/WEB-INF/lib/gson-2.3.1.jar


Action:

Correct the classpath of your application so that it contains a single, compatible version of com.google.gson.GsonBuilder

14-Oct-2019 17:27:33.004 SEVERE [localhost-startStop-1] org.apache.catalina.core.ContainerBase.addChildInternal ContainerBase.addChild: start:
 org.apache.catalina.LifecycleException: Failed to start component [StandardEngine[Catalina].StandardHost[localhost].StandardContext[/admin]]
        at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:167)
        at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:754)
        at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:730)
        at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:734)
        at org.apache.catalina.startup.HostConfig.deployWAR(HostConfig.java:980)
        at org.apache.catalina.startup.HostConfig$DeployWar.run(HostConfig.java:1851)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
        at java.util.concurrent.FutureTask.run(FutureTask.java:266)

当前引入的gson版本是2.3的，在Maven dependience中查看有2.8.5的版本依赖，可是我全文搜索都不知道项目原来在哪里引入过gson的依赖。

原来父pom中有spring-boot-starter-parent

<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>2.0.1.RELEASE</version>
 </parent>

点击上面的spring-boot-starter-parent，查看其源码，发现它又继承了spring-boot-dependencies：

<parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-dependencies</artifactId>
        <version>2.0.1.RELEASE</version>
        <relativePath>../../spring-boot-dependencies</relativePath>
    </parent>


点击上面的spring-boot-dependencies，查看其源码，搜索gson，发现这里确实已经引入了gson的依赖：2.8.5

解决办法：pom.xml 里引入依赖时，删掉 <version>2.3</version>这一行，Spring Boot 会自动查找匹配最合适的版本。