SpringBoot启动时报错： java.lang.NoClassDefFoundError: javax/servlet/Servlet

缺乏、安全感 2023-02-27 12:29 5阅读 0赞

经过一番百度和谷歌后，问题的发生根源渐渐清晰：**jar包冲突导致**。  
报错时，工程中引用的maven依赖如下：

<dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-gateway</artifactId>
            </dependency>
    
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-test</artifactId>
                <scope>test</scope>
            </dependency>
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
            </dependency>
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-starter-alibaba-nacos-config</artifactId>
            </dependency>
    
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-data-redis</artifactId>
            </dependency>
    
            <dependency>
                  <groupId>org.apache.commons</groupId>
                  <artifactId>commons-lang3</artifactId>
              </dependency>
    
              <dependency>
                  <groupId>com.alibaba</groupId>
                  <artifactId>fastjson</artifactId>
              </dependency>
    
              <dependency>
                  <groupId>org.mybatis.spring.boot</groupId>
                  <artifactId>mybatis-spring-boot-starter</artifactId>
              </dependency>
    
              <dependency>
                  <groupId>mysql</groupId>
                  <artifactId>mysql-connector-java</artifactId>
                  <scope>runtime</scope>
              </dependency>
    
              <dependency>
                  <groupId>com.alibaba</groupId>
                  <artifactId>druid-spring-boot-starter</artifactId>
              </dependency>
    
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
                <optional>true</optional>
            </dependency>
    
            <dependency>
                <groupId>org.apache.commons</groupId>
                <artifactId>commons-pool2</artifactId>
            </dependency>
    
        </dependencies>

经过一一排除，发现是alibaba的druid-spring-boot-starter的jar包导致，将其注释掉后：

<dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-starter-gateway</artifactId>
            </dependency>
    
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-test</artifactId>
                <scope>test</scope>
            </dependency>
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
            </dependency>
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-starter-alibaba-nacos-config</artifactId>
            </dependency>
    
            <dependency>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-starter-data-redis</artifactId>
            </dependency>
    
            <dependency>
                  <groupId>org.apache.commons</groupId>
                  <artifactId>commons-lang3</artifactId>
              </dependency>
    
              <dependency>
                  <groupId>com.alibaba</groupId>
                  <artifactId>fastjson</artifactId>
              </dependency>
    
              <dependency>
                  <groupId>org.mybatis.spring.boot</groupId>
                  <artifactId>mybatis-spring-boot-starter</artifactId>
              </dependency>
    
              <dependency>
                  <groupId>mysql</groupId>
                  <artifactId>mysql-connector-java</artifactId>
                  <scope>runtime</scope>
              </dependency>
    
    
    
    
    
    
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
                <optional>true</optional>
            </dependency>
    
            <dependency>
                <groupId>org.apache.commons</groupId>
                <artifactId>commons-pool2</artifactId>
            </dependency>
    
        </dependencies>

SpringBoot项目就可以正常启动了，至于为什么是这样，我也没搞清楚，欢迎大佬指点迷津！可以直接在下方评论，多谢多谢！

有的小伙伴说，我的项目中没有alibaba的druid-spring-boot-starter的jar包也出现这个错误了，那就麻烦你一一排除了！