先看具体日志：
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaConfiguration': Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [org/springframework/boot/autoconfigure/jdbc/DataSourceConfiguration$Hikari.class]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.boot.autoconfigure.jdbc.DataSourceInitializerInvoker': Invocation of init method failed; nested exception is org.springframework.jdbc.datasource.init.ScriptStatementFailedException: Failed to execute SQL script statement #2 of URL [jar:file:/home/wlf/springboot-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/schema.sql]: insert into t_user(user_name, pass_word, role_value) select 'admin', '123456', 'Admin' from dual where not exists(select user_name, pass_word, role_value from t_user where user_name='admin' and pass_word='123456' and role_value='Admin'); nested exception is java.sql.SQLException: Field 'id' doesn't have a default value at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:769) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:218) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1325) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1171) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:555) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:392) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1305) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1144) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:555) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1105) ~[spring-context-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867) ~[spring-context-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549) ~[spring-context-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142) ~[spring-boot-2.1.3.RELEASE.jar!/:2.1.3.RELEASE] at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775) ~[spring-boot-2.1.3.RELEASE.jar!/:2.1.3.RELEASE] at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) ~[spring-boot-2.1.3.RELEASE.jar!/:2.1.3.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:316) ~[spring-boot-2.1.3.RELEASE.jar!/:2.1.3.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) ~[spring-boot-2.1.3.RELEASE.jar!/:2.1.3.RELEASE] at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248) ~[spring-boot-2.1.3.RELEASE.jar!/:2.1.3.RELEASE] at com.crocodile.springboot.SpringbootApplication.main(SpringbootApplication.java:10) ~[classes!/:0.0.1-SNAPSHOT] at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na] at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na] at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na] at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na] at org.springframework.boot.loader.MainMethodRunner.run(MainMethodRunner.java:48) ~[springboot-0.0.1-SNAPSHOT.jar:0.0.1-SNAPSHOT] at org.springframework.boot.loader.Launcher.launch(Launcher.java:87) ~[springboot-0.0.1-SNAPSHOT.jar:0.0.1-SNAPSHOT] at org.springframework.boot.loader.Launcher.launch(Launcher.java:50) ~[springboot-0.0.1-SNAPSHOT.jar:0.0.1-SNAPSHOT] at org.springframework.boot.loader.JarLauncher.main(JarLauncher.java:51) ~[springboot-0.0.1-SNAPSHOT.jar:0.0.1-SNAPSHOT] Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [org/springframework/boot/autoconfigure/jdbc/DataSourceConfiguration$Hikari.class]: Initialization of bean failed; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.boot.autoconfigure.jdbc.DataSourceInitializerInvoker': Invocation of init method failed; nested exception is org.springframework.jdbc.datasource.init.ScriptStatementFailedException: Failed to execute SQL script statement #2 of URL [jar:file:/home/wlf/springboot-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/schema.sql]: insert into t_user(user_name, pass_word, role_value) select 'admin', '123456', 'Admin' from dual where not exists(select user_name, pass_word, role_value from t_user where user_name='admin' and pass_word='123456' and role_value='Admin'); nested exception is java.sql.SQLException: Field 'id' doesn't have a default value at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:601) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:277) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1247) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1167) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:857) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:760) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] ... 36 common frames omitted Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'org.springframework.boot.autoconfigure.jdbc.DataSourceInitializerInvoker': Invocation of init method failed; nested exception is org.springframework.jdbc.datasource.init.ScriptStatementFailedException: Failed to execute SQL script statement #2 of URL [jar:file:/home/wlf/springboot-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/schema.sql]: insert into t_user(user_name, pass_word, role_value) select 'admin', '123456', 'Admin' from dual where not exists(select user_name, pass_word, role_value from t_user where user_name='admin' and pass_word='123456' and role_value='Admin'); nested exception is java.sql.SQLException: Field 'id' doesn't have a default value at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1762) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:593) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:224) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveNamedBean(DefaultListableBeanFactory.java:1115) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveBean(DefaultListableBeanFactory.java:407) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:341) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:335) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.boot.autoconfigure.jdbc.DataSourceInitializerPostProcessor.postProcessAfterInitialization(DataSourceInitializerPostProcessor.java:55) ~[spring-boot-autoconfigure-2.1.3.RELEASE.jar!/:2.1.3.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsAfterInitialization(AbstractAutowireCapableBeanFactory.java:429) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1766) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:593) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] ... 46 common frames omitted Caused by: org.springframework.jdbc.datasource.init.ScriptStatementFailedException: Failed to execute SQL script statement #2 of URL [jar:file:/home/wlf/springboot-0.0.1-SNAPSHOT.jar!/BOOT-INF/classes!/schema.sql]: insert into t_user(user_name, pass_word, role_value) select 'admin', '123456, 'Admin' from dual where not exists(select user_name, pass_word, role_value from t_user where user_name='admin' and pass_word='123456' and role_value='Admin'); nested exception is java.sql.SQLException: Field 'id' doesn't have a default value at org.springframework.jdbc.datasource.init.ScriptUtils.executeSqlScript(ScriptUtils.java:509) ~[spring-jdbc-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.jdbc.datasource.init.ResourceDatabasePopulator.populate(ResourceDatabasePopulator.java:238) ~[spring-jdbc-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.jdbc.datasource.init.DatabasePopulatorUtils.execute(DatabasePopulatorUtils.java:48) ~[spring-jdbc-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.boot.autoconfigure.jdbc.DataSourceInitializer.runScripts(DataSourceInitializer.java:210) ~[spring-boot-autoconfigure-2.1.3.RELEASE.jar!/:2.1.3.RELEASE] at org.springframework.boot.autoconfigure.jdbc.DataSourceInitializer.createSchema(DataSourceInitializer.java:104) ~[spring-boot-autoconfigure-2.1.3.RELEASE.jar!/:2.1.3.RELEASE] at org.springframework.boot.autoconfigure.jdbc.DataSourceInitializerInvoker.afterPropertiesSet(DataSourceInitializerInvoker.java:64) ~[spring-boot-autoconfigure-2.1.3.RELEASE.jar!/:2.1.3.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1821) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1758) ~[spring-beans-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] ... 60 common frames omitted Caused by: java.sql.SQLException: Field 'id' doesn't have a default value at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129) ~[mysql-connector-java-8.0.15.jar!/:8.0.15] at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97) ~[mysql-connector-java-8.0.15.jar!/:8.0.15] at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:122) ~[mysql-connector-java-8.0.15.jar!/:8.0.15] at com.mysql.cj.jdbc.StatementImpl.executeInternal(StatementImpl.java:782) ~[mysql-connector-java-8.0.15.jar!/:8.0.15] at com.mysql.cj.jdbc.StatementImpl.execute(StatementImpl.java:666) ~[mysql-connector-java-8.0.15.jar!/:8.0.15] at com.zaxxer.hikari.pool.ProxyStatement.execute(ProxyStatement.java:95) ~[HikariCP-3.2.0.jar!/:na] at com.zaxxer.hikari.pool.HikariProxyStatement.execute(HikariProxyStatement.java) ~[HikariCP-3.2.0.jar!/:na] at org.springframework.jdbc.datasource.init.ScriptUtils.executeSqlScript(ScriptUtils.java:488) ~[spring-jdbc-5.1.5.RELEASE.jar!/:5.1.5.RELEASE] ... 67 common frames omitted
从上述日志中看到，启动Spring boot时先去初始化Spring data JPA，但没有加载到数据源DataSource对象。那为啥数据源会加载失败，其实引发的原因是执行初始化脚本执行失败。先看application.properties文件配置的数据源：
#mysql数据库配置 spring.datasource.url=jdbc:mysql://localhost:3306/test?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC spring.datasource.username=root spring.datasource.password=123456 spring.datasource.driver-class-name=com.mysql.jdbc.Driver spring.datasource.initialization-mode=always
最后一行指定了数据源初始化时必须去执行我的预置脚本schema.sql：
create table if not exists t_user ( id bigint not null auto_increment, user_name varchar(255) not null, pass_word varchar(255) not null, role_value varchar(255) not null, primary key (id) ); insert into t_user(user_name, pass_word, role_value) select 'admin', '123456', 'admin' from dual where not exists(select user_name, pass_word, role_value from t_user where user_name='admin' and pass_word='123456' and role_value='admin');
重启Spring boot时为防止重复建表用了if not exists、重复插入用了insert into...select from dual where not exists，都是先看有没有，没有了再操作。因为这里的id是自增长的，所以就算我的插入语句不指定id，mysql也会默认自动给id赋一个自增长的值。如果真按以上执行了，那应该不会出现问题才对。但事实很明显，Spring boot不按此套路来。看下我的实体类中主键ID的定义：
@Entity @Table(name = "T_USER") public class User implements Serializable { @Id @GeneratedValue private Long id; private String userName; private String passWord; private String roleValue; ... }
以上实例类中我们指定ID是自增长的，可是这个增长不是mysql的自增，而是Spring Data JPA去设置的。我们看下@GeneratedValue究竟给我们设置了怎样的生成策略：
@Target({ElementType.METHOD, ElementType.FIELD}) @Retention(RetentionPolicy.RUNTIME) public @interface GeneratedValue { GenerationType strategy() default GenerationType.AUTO; String generator() default ""; }
它默认是GenerationType.AUTO，若想让mysql接手设置自动增长，必须用这个：
@Id @GeneratedValue(strategy = GenerationType.IDENTITY) private Long id;
生成类型有四种：
- TABLE：使用一个特定的数据库表来保存主键，也就是你可以自己指定哪张表。
- SEQUENCE：根据底层数据库的序列来生成主键，当然条件是得数据库支持序列的生成。
- IDENTITY：主键由数据库自动生成（主要是自动增长型），比如mysql就会设置扩展属性为auto_increment
- AUTO：主键由程序控制，程序自动生成表，比如在mysql里会自动创建表hibernate_sequence，每次新增都会读取next_val值作为自增长ID。
我们看下使用AUTO生成的表结构：
mysql> desc t_user; +------------+--------------+------+-----+---------+-------+ | Field | Type | Null | Key | Default | Extra | +------------+--------------+------+-----+---------+-------+ | id | bigint(20) | NO | PRI | NULL | | | pass_word | varchar(255) | YES | | NULL | | | role_value | varchar(255) | YES | | NULL | | | user_name | varchar(255) | YES | | NULL | | +------------+--------------+------+-----+---------+-------+ 4 rows in set (0.00 sec)
直接insert不带主键默认值必然报错：
mysql> insert into t_user(user_name, pass_word, role_value) values ('wlf', '123', 'sales'); ERROR 1364 (HY000): Field 'id' doesn't have a default value
换IDENTITY试试：
mysql> desc t_user; +------------+--------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +------------+--------------+------+-----+---------+----------------+ | id | bigint(20) | NO | PRI | NULL | auto_increment | | user_name | varchar(255) | NO | | NULL | | | pass_word | varchar(255) | NO | | NULL | | | role_value | varchar(255) | NO | | NULL | | +------------+--------------+------+-----+---------+----------------+ 4 rows in set (0.01 sec)
我们看到mysql的自增长属性带上了，这时再使用不带自增长的id字段入库成功了：
mysql> insert into t_user(user_name, pass_word, role_value) values('aaa', '123', 'sales'); Query OK, 1 row affected (0.02 sec)
另外需要注意，mysql里没有建表前你指定主键生成策略为IDENTITY会加上自增长属性，但如果你开始是AUTO的，后来再改为IDENTITY的，那么你需要手动去mysql里修改约束，自己加上自增长属性，或者drop表重来。