1.spring框架版本升级

<spring.version>5.2.1.RELEASE</spring.version>

会报错：

o.s.web.context.support.XmlWebApplicationContext Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter': Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter]: 
Constructor threw exception; nested exception is java.lang.NoClassDefFoundError: com/fasterxml/jackson/databind/exc/InvalidDefinitionException

原因是：spring和jackson相关版本不兼容

    <dependency>
      <groupId>com.fasterxml.jackson.core</groupId>
      <artifactId>jackson-databind</artifactId>
      <version>2.10.1</version>
    </dependency>

2.其他工具包升级

    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>4.0.1</version>
    </dependency>

    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.5.3</version>
    </dependency>
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis-spring</artifactId>
      <version>2.0.3</version>
    </dependency>

    <dependency>
      <groupId>com.mchange</groupId>
      <artifactId>c3p0</artifactId>
      <version>0.9.5.4</version>
    </dependency>

3.redis升级出现很多错误

表明redis版本进行了较大改动，考虑修改成本，以及本项目所使用的是简单的redis功能，就不进行升级

4.企业升级主要步骤

• step1.在本地或者开发环境尝试升级，确保功能正常（开发过程中的测试用例）
• step2.提交改动到线上代码库，由QA进行各项测试，包括功能和性能
• step3.灰度发布，即逐步上线（一组一组服务器进行上线）
• step4.全量上线