Spring Boot 多数据库：没有 EntityManagerFactoryBuilder 类型的合格 bean

我们的 Spring Boot 应用程序中有两个数据库，称为源数据库和目标数据库。这是这些的配置

源配置

package com.alex.myapp.config;

import javax.persistence.EntityManagerFactory;
import javax.sql.DataSource;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.core.env.Environment;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.jdbc.datasource.DriverManagerDataSource;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.annotation.EnableTransactionManagement;

@Configuration
@EnableTransactionManagement
@EnableJpaRepositories(
        entityManagerFactoryRef = "sourceManagerFactory",
        transactionManagerRef = "sourceTransactionManager",
        basePackages = {"com.alex.myapp.source.repository"}
)
public class SourceDbConfiguration {

    @Autowired
    private Environment env;

    @Primary
    @Bean(name = "sourceManagerFactory")
    public LocalContainerEntityManagerFactoryBean
    sourceManagerFactory(EntityManagerFactoryBuilder builder) {
        LocalContainerEntityManagerFactoryBean em = builder
                .dataSource(sourceDataSource())
                .packages("com.alex.myapp.source.entity")
                .persistenceUnit("source")
                .build();
        return em;
    }

    @Primary
    @Bean
    public DataSource sourceDataSource() {
        DriverManagerDataSource dataSource
                = new DriverManagerDataSource();
        dataSource.setDriverClassName(
                env.getProperty("spring.datasource.driver-class-name"));
        dataSource.setUrl(env.getProperty("spring.datasource.url"));
        dataSource.setUsername(env.getProperty("spring.datasource.username"));
        dataSource.setPassword(env.getProperty("spring.datasource.password"));

        return dataSource;
    }

    @Primary
    @Bean(name = "sourceTransactionManager")
    public PlatformTransactionManager sourceTransactionManager(
            @Qualifier("sourceManagerFactory") EntityManagerFactory
                    sourceManagerFactory
    ) {
        return new JpaTransactionManager(sourceManagerFactory);
    }
}

目标配置

package com.alex.myapp.config;

import javax.persistence.EntityManagerFactory;
import javax.sql.DataSource;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import org.springframework.core.env.Environment;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.jdbc.datasource.DriverManagerDataSource;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.transaction.PlatformTransactionManager;
import org.springframework.transaction.annotation.EnableTransactionManagement;

@Configuration
@EnableTransactionManagement
@EnableJpaRepositories(
        entityManagerFactoryRef = "targetManagerFactory",
        transactionManagerRef = "targetTransactionManager",
        basePackages = {"com.alex.myapp.target.repository"}
)
public class TargetDbConfiguration {

    @Autowired
    private Environment env;

    @Primary
    @Bean(name = "targetManagerFactory")
    public LocalContainerEntityManagerFactoryBean
    targetManagerFactory(EntityManagerFactoryBuilder builder) {
        LocalContainerEntityManagerFactoryBean em = builder
                .dataSource(targetDataSource())
                .packages("com.alex.myapp.target.entity")
                .persistenceUnit("target")
                .build();
        return em;
    }

    @Primary
    @Bean
    public DataSource targetDataSource() {
        DriverManagerDataSource dataSource
                = new DriverManagerDataSource();
        dataSource.setDriverClassName(
                env.getProperty("target.datasource.driver-class-name"));
        dataSource.setUrl(env.getProperty("target.datasource.url"));
        dataSource.setUsername(env.getProperty("target.datasource.username"));
        dataSource.setPassword(env.getProperty("target.datasource.password"));

        return dataSource;
    }

    @Bean(name = "targetTransactionManager")
    public PlatformTransactionManager targetTransactionManager(
            @Qualifier("targetManagerFactory") EntityManagerFactory
                    targetManagerFactory) {
        return new JpaTransactionManager(targetManagerFactory);
    }
}

当我尝试启动服务器时，它会抛出下面提到的错误

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2018-09-19 13:30:53 - Application run failed
org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'sourceManagerFactory' defined in class path resource [com/alex/myapp/config/SourceDbConfiguration.class]: Unsatisfied dependency expressed through method 'sourceManagerFactory' parameter 0; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type 'org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder' available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}
    at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:732)
    at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:474)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1247)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1096)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:535)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495)
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
    at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1089)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:859)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:550)

以防万一，如果我注释掉目标配置类级别注释，一切正常。两个数据库配置似乎相互冲突。

@Primary必须准确地用在所需类型中的一种 bean 上。

摘自@Primary javadoc https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/context/annotation/Primary.html

指示当多个候选者有资格自动装配单值依赖项时，应优先考虑某个 bean。如果候选者中恰好存在一个“主要”bean，则它将是自动装配的值。