如何懒加载Spring Boot数据源？spring.data

Question

我有一个使用 spring-boot 框架编写的应用程序，定义了一个 mysql 的 DataSource:

spring.datasource.url=...
spring.datasource.username=...
spring.datasource.password=...

我将该工具作为命令行应用程序由cronjob触发运行。在所有运行的80％中，我可以完全退出该工具而无需联系数据库：

@Controller
public class MainController {
    @Autowired
    private MyService myService;

    public void evaluate() {
           if (condition == true) myService.run();
           else System.exit(0);
    } 
}

@Service
@Lazy
public class MyService {
    @Autowired
    private JdbcTemplate jdbc;

    public void run() {
       jdbc.execute(sql);
    }
}

问题：我希望完全阻止Spring初始化数据库。因此，如果例如数据库停机或主机不可访问（可以使用spring.datasource.url=localhostX进行测试），那么工具仍应该是可运行的。

是否可能延迟数据源初始化直到真正需要它？

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaConfiguration.class]: Invocation of init method failed; nested exception is org.hibernate.service.spi.ServiceException: Unable to create requested service [org.hibernate.engine.jdbc.env.spi.JdbcEnvironment]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1778) ~[spring-beans-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:593) ~[spring-beans-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1105) ~[spring-context-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:867) ~[spring-context-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549) ~[spring-context-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:744) ~[spring-boot-2.1.9.RELEASE.jar:2.1.9.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:391) ~[spring-boot-2.1.9.RELEASE.jar:2.1.9.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:312) ~[spring-boot-2.1.9.RELEASE.jar:2.1.9.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1215) ~[spring-boot-2.1.9.RELEASE.jar:2.1.9.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1204) ~[spring-boot-2.1.9.RELEASE.jar:2.1.9.RELEASE]
Caused by: org.hibernate.service.spi.ServiceException: Unable to create requested service [org.hibernate.engine.jdbc.env.spi.JdbcEnvironment]
    at org.hibernate.service.internal.AbstractServiceRegistryImpl.createService(AbstractServiceRegistryImpl.java:275) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:237) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:214) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.id.factory.internal.DefaultIdentifierGeneratorFactory.injectServices(DefaultIdentifierGeneratorFactory.java:152) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.service.internal.AbstractServiceRegistryImpl.injectDependencies(AbstractServiceRegistryImpl.java:286) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.service.internal.AbstractServiceRegistryImpl.initializeService(AbstractServiceRegistryImpl.java:243) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.service.internal.AbstractServiceRegistryImpl.getService(AbstractServiceRegistryImpl.java:214) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.boot.internal.InFlightMetadataCollectorImpl.<init>(InFlightMetadataCollectorImpl.java:179) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.boot.model.process.spi.MetadataBuildingProcess.complete(MetadataBuildingProcess.java:119) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.metadata(EntityManagerFactoryBuilderImpl.java:904) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:935) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:58) ~[spring-orm-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365) ~[spring-orm-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:391) ~[spring-orm-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:378) ~[spring-orm-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.afterPropertiesSet(LocalContainerEntityManagerFactoryBean.java:341) ~[spring-orm-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1837) ~[spring-beans-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1774) ~[spring-beans-5.1.10.RELEASE.jar:5.1.10.RELEASE]
    ... 15 common frames omitted
Caused by: org.hibernate.HibernateException: Access to DialectResolutionInfo cannot be null when 'hibernate.dialect' not set
    at org.hibernate.engine.jdbc.dialect.internal.DialectFactoryImpl.determineDialect(DialectFactoryImpl.java:100) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.engine.jdbc.dialect.internal.DialectFactoryImpl.buildDialect(DialectFactoryImpl.java:54) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.initiateService(JdbcEnvironmentInitiator.java:137) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.engine.jdbc.env.internal.JdbcEnvironmentInitiator.initiateService(JdbcEnvironmentInitiator.java:35) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.boot.registry.internal.StandardServiceRegistryImpl.initiateService(StandardServiceRegistryImpl.java:94) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    at org.hibernate.service.internal.AbstractServiceRegistryImpl.createService(AbstractServiceRegistryImpl.java:263) ~[hibernate-core-5.3.12.Final.jar:5.3.12.Final]
    ... 32 common frames omitted

- membersound

---

那真的是你所有的配置吗？没有连接池吗？因为我认为实际上连接池的创建在启动时会失败，因为它将无法预先填充到最小请求的连接数。 - Gimby

实际上，Spring 默认使用 Hikari 连接池。我想继续使用它，但是我该如何延迟 Hikari 连接池的初始化呢？ - membersound

也许可以排除自动配置。https://dev59.com/nqzla4cB1Zd3GeqPDdoD - user7294900

但是我如何在罕见的20%情况下包含数据源自动配置呢？因为那时我需要它，而且在启动cli应用程序之前我不知道条件。 - membersound

你可以尝试将Hikari的minimumIdle设置为0... 这样应该可以阻止它预初始化连接。文档：https://github.com/brettwooldridge/HikariCP#configuration-knobs-baby - Gimby

Answer 1

如在Spring文档中所述(https://docs.spring.io/spring-boot/docs/2.1.13.RELEASE/reference/html/boot-features-sql.html)：

Spring Data JPA repositories 支持三种不同的引导模式：默认模式、延迟模式和懒加载模式。为启用延迟或懒加载引导，请将 spring.data.jpa.repositories.bootstrap-mode 设置为 deferred 或 lazy。

因此，在应用程序属性（或yaml）文件中尝试以下配置:

spring.data.jpa.repositories.bootstrap-mode=lazy

- Maxim Savenko

---

请添加@SpringBootApplication(exclude = HibernateJpaAutoConfiguration.class)。 - Ahmad Nadeem

Answer 2

@SpringBootApplication(exclude = HibernateJpaAutoConfiguration.class)

在启动时，某种方式下Hikari Pool和Hibernate似乎会相互影响。如果数据源不存在，则启动将失败。

使用上面的排除方法，并结合@Lazy注释以按预期延迟初始化。

但这仅限于我不使用Hibernate的情况下才有效。

- membersound

---

请添加spring.data.jpa.repositories.bootstrap-mode=lazy - Ahmad Nadeem

Answer 3

当使用Hibernate作为JPA实现时，即使在应用程序启动时初始化bean，通过设置这两个Hibernate特定属性，我也能够避免连接到数据库 -

spring:
  jpa:
    properties:
      hibernate:
        temp:
          use_jdbc_metadata_defaults: false
        hbm2ddl:
            auto: none

以下是Hibernate文档中这些属性的意义：

hibernate.temp.use_jdbc_metadata_defaults (例如true（默认值）或false)

此设置用于控制我们是否应在数据库不可用时（主要在工具使用中）查询JDBC元数据以确定某些设置的默认值。

和这里

hibernate.hbm2ddl.auto (例如none（默认值），create-only，drop，create，create-drop，validate和update)

设置为自动执行SchemaManagementTool操作作为SessionFactory生命周期的一部分。有效选项由Action枚举的externalHbm2ddlName值定义：

none 不执行任何操作。

所以，在设置属性之后，只有在执行 SQL 查询时才会建立 JDBC 连接。

- SKumar

Answer 4

从Springboot 2.2开始，这是可能的。

在application.properties中添加以下属性。

spring.main.lazy-initialization=true

点击这里以获取更多详细信息。

- MyTwoCents

---

你确定吗？我尝试过了，但它没有跳过DataSource初始化(java.sql.SQLNonTransientConnectionException: Could not connect to address=(host=localhostx)(port=3306)(type=master) : localhostx)。 - membersound

这不会影响所有的Bean吗？ - user7294900

是的，你说得对，这将使所有的bean在第一次调用时按需初始化。 - MyTwoCents