背景：

升级了 spring boot 版本，从1.x 升级到了2.x

报错如下：

ERROR org.springframework.boot.SpringApplication - Application run failed
java.lang.NoSuchMethodError: org.springframework.boot.builder.SpringApplicationBuilder.<init>([Ljava/lang/Object;)V
    at org.springframework.cloud.bootstrap.BootstrapApplicationListener.bootstrapServiceContext(BootstrapApplicationListener.java:157)
    at org.springframework.cloud.bootstrap.BootstrapApplicationListener.onApplicationEvent(BootstrapApplicationListener.java:98)
    at org.springframework.cloud.bootstrap.BootstrapApplicationListener.onApplicationEvent(BootstrapApplicationListener.java:64)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139)
    at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:127)
    at org.springframework.boot.context.event.EventPublishingRunListener.environmentPrepared(EventPublishingRunListener.java:74)
    at org.springframework.boot.SpringApplicationRunListeners.environmentPrepared(SpringApplicationRunListeners.java:54)
    at org.springframework.boot.SpringApplication.prepareEnvironment(SpringApplication.java:358)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:317)
    at org.springframework.boot.builder.SpringApplicationBuilder.run(SpringApplicationBuilder.java:137)
 

寻找原因：

1. 一开始查了下源码，发现自己并看不懂

2.还是老老实实排查jar 包吧，项目中引入了 spring-cloud-starter-feign， 这个 jar 里引入了 spring-cloud 的东西。spring-cloud 和 spring-boot 版本冲突

解决过程：

1.引入 spring-cloud 依赖

<dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>Finchley.RELEASE</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>

 2.替换 spring-cloud-starter-feign 为 spring-cloud-starter-openfeign

3. 重新启动报错：

ERROR o.s.boot.SpringApplication - Application run failed 
org.springframework.context.ApplicationContextException: Unable to start web server; nested exception is org.springframework.boot.web.server.WebServerException: Unable to start embedded Tomcat
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:156)
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:544)
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:141)
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:747)
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:315)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226)
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215)

仔细查看了一下 错误日志发现

ERROR com.zaxxer.hikari.pool.HikariPool - HikariPool-1 - Exception during pool initialization. 
java.sql.SQLNonTransientConnectionException: Cannot load connection class because of underlying exception: com.mysql.cj.exceptions.WrongArgumentException: Malformed database URL, failed to parse the connection string near ';useUnicode=true&characterEncoding=utf-8'.
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:110)
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:89)
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:63)
	at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:73)
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:79)
	at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:131)
	at com.mysql.cj.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:219)
	at com.zaxxer.hikari.util.DriverDataSource.getConnection(DriverDataSource.java:138)
	at com.zaxxer.hikari.pool.PoolBase.newConnection(PoolBase.java:353)
	at com.zaxxer.hikari.pool.PoolBase.newPoolEntry(PoolBase.java:201)
	at com.zaxxer.hikari.pool.HikariPool.createPoolEntry(HikariPool.java:473)
	at com.zaxxer.hikari.pool.HikariPool.checkFailFast(HikariPool.java:562)
	at com.zaxxer.hikari.pool.HikariPool.<init>(HikariPool.java:115)

看到这里明白了，是 数据源链接配置的问题。

因为：升级了 springboot 版本，mysql 驱动版本也升级了，不支持 jdbc:mysql://localhost:3306/customer?autoReconnect=true&useUnicode=true&characterEncoding=utf-8。改成 jdbc:mysql://192.168.1.204:3306/customer?autoReconnect=true&useUnicode=true&characterEncoding=utf-8 启动成功