Java 在 DAO 中使用多个实体管理器
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时间：2020-08-13 06:04:14 来源:igfitidea点击:
Using Multiple Entity managers in DAO
提问by anasanjaria
I'm trying to configure Spring+Hibernate+JPA for work with two databases ( one for write only i.e insertion & updation & other is only for retrieval.
我正在尝试配置 Spring+Hibernate+JPA 以使用两个数据库（一个只用于写入，即插入和更新，另一个仅用于检索。
I did some research & found these possible solutions:
我做了一些研究并找到了这些可能的解决方案：
- http://www.studytrails.com/frameworks/spring/spring-hibernate-jpa.jsp
- Multiple database with Spring+Hibernate+JPA
- How do I connect to multiple databases using JPA?
- http://www.studytrails.com/frameworks/spring/spring-hibernate-jpa.jsp
- Spring+Hibernate+JPA 多数据库
- 如何使用 JPA 连接到多个数据库？
But I stuck at one place & getting this error
但我卡在一个地方并收到此错误
No qualifying bean of type [javax.persistence.EntityManagerFactory] is defined: expected single matching bean but found 2: entityManagerFactoryReadOnly,entityManagerFactoryWriteOnly
What am I doing wrong ?
我究竟做错了什么 ？
persistent.read.only.xml:
持久性.read.only.xml：
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"
xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
<persistence-unit name="readOnly" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<class>com.demo.domain.Contact</class>
</persistence-unit>
</persistence>
persistent.write.only.xml:
持久化.write.only.xml：
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"
xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
<persistence-unit name="writeOnly" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<class>com.demo.domain.Contact</class>
</persistence-unit>
</persistence>
mcv-dispatcher-servlet.xml:
mcv-dispatcher-servlet.xml:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:jee="http://www.springframework.org/schema/jee"
xmlns:lang="http://www.springframework.org/schema/lang" xmlns:p="http://www.springframework.org/schema/p"
xmlns:tx="http://www.springframework.org/schema/tx" xmlns:util="http://www.springframework.org/schema/util"
xmlns:oxm="http://www.springframework.org/schema/oxm"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-3.2.xsd
http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-3.2.xsd
http://www.springframework.org/schema/jee http://www.springframework.org/schema/jee/spring-jee.xsd
http://www.springframework.org/schema/lang http://www.springframework.org/schema/lang/spring-lang.xsd
http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx-3.2.xsd
http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-3.2.xsd
http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd
http://www.springframework.org/schema/oxm http://www.springframework.org/schema/oxm/spring-oxm-3.2.xsd">
<!-- Activates various annotations to be detected in bean classes -->
<context:annotation-config />
<!-- Scans the classpath for annotated components that will be auto-registered
as Spring beans. For example @Controller and @Service. Make sure to set the
correct base-package -->
<context:component-scan base-package="com.demo" />
<!-- Setup a simple strategy: 1. Take all the defaults. 2. Return XML by
default when not sure. -->
<!-- Total customization - see below for explanation. -->
<bean id="cnManager"
class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
<property name="favorPathExtension" value="true" />
<property name="ignoreAcceptHeader" value="true" />
<property name="defaultContentType" value="application/json" />
<property name="useJaf" value="false" />
<property name="mediaTypes">
<map>
<entry key="json" value="application/json" />
<entry key="xml" value="application/xml" />
</map>
</property>
</bean>
<!-- Make this available across all of Spring MVC -->
<mvc:annotation-driven
content-negotiation-manager="cnManager" />
<bean class="com.demo.view.MvcConfiguringPostProcessor" />
<bean id="propertyConfigurer"
class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer"
p:location="/WEB-INF/jdbc.properties" />
<!-- ******************************************************************** -->
<!-- START: Multiple C3P0 data-sources for DB instance -->
<!-- ******************************************************************** -->
<!-- https://stackoverflow.com/questions/12922351/can-i-use-multiple-c3p0-datasources-for-db-instance -->
<!-- Using Apache DBCP Data Sources -->
<bean id="dataSource"
abstract="true" >
<property name="driverClass" value="${db.driverClassName}" />
<property name="user" value="${db.username}" />
<property name="password" value="${db.password}" />
<property name="idleConnectionTestPeriod" value="${db.idleConnectionTestPeriod}" />
<property name="preferredTestQuery" value="select 1" />
<property name="testConnectionOnCheckin" value="true" />
</bean>
<bean id="dataSourceReadOnly"
parent="dataSource"
class="com.mchange.v2.c3p0.ComboPooledDataSource"
destroy-method="close">
<property name="jdbcUrl" value="${db.readOnlyDataBaseUrl}" />
</bean>
<bean id="dataSourceWriteOnly"
parent="dataSource"
class="com.mchange.v2.c3p0.ComboPooledDataSource"
destroy-method="close">
<property name="jdbcUrl" value="${db.writeOnlyDataBaseUrl}" />
</bean>
<!-- ******************************************************************** -->
<!-- END: Multiple C3P0 data-sources for DB instance -->
<!-- ******************************************************************** -->
<bean id="jpaVendorProvider"
class="org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter">
<property name="database" value="MYSQL" />
<property name="databasePlatform" value="${db.dialect}" />
<property name="showSql" value="true" />
<property name="generateDdl" value="true" />
</bean>
<!-- <bean -->
<!-- class="org.springframework.orm.jpa.support.PersistenceAnnotationBeanPostProcessor"> -->
<!-- <property name="defaultPersistenceUnitName" value="readOnly" /> -->
<!-- </bean> -->
<bean id="persistenceUnitManager"
class="org.springframework.orm.jpa.persistenceunit.DefaultPersistenceUnitManager">
<!-- defining multiple persistence unit -->
<property name="persistenceXmlLocations">
<list>
<value>/META-INF/persistence.read.only.xml</value>
<value>/META-INF/persistence.write.only.xml</value>
</list>
</property>
<property name="defaultDataSource" ref="dataSourceReadOnly" />
<property name="dataSources">
<map>
<entry key="readOnlyDsKey" value-ref="dataSourceReadOnly" />
<entry key="writeOnlyDsKey" value-ref="dataSourceWriteOnly" />
</map>
</property>
</bean>
<bean id="entityManagerFactoryReadOnly"
class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<!-- <property name="dataSource" ref="dataSourceReadOnly" /> -->
<property name="persistenceUnitManager" ref="persistenceUnitManager" />
<property name="jpaVendorAdapter" ref="jpaVendorProvider" />
<property name="persistenceUnitName" value="readOnly" />
<!-- entityManagerFactory does not specify persistenceUnitName property
because we're defining more than one persistence unit -->
<!-- <property name="persistenceUnitName" value="hello_mysql" /> -->
<!-- <property name="persistenceXmlLocation" value="/META-INF/persistence.xml" /> -->
</bean>
<bean id="entityManagerFactoryWriteOnly"
class="org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean">
<!-- <property name="dataSource" ref="dataSourceWriteOnly" /> -->
<property name="persistenceUnitManager" ref="persistenceUnitManager" />
<property name="jpaVendorAdapter" ref="jpaVendorProvider" />
<property name="persistenceUnitName" value="writeOnly" />
</bean>
<!-- ******************************************************************** -->
<!-- Mark bean transactions as annotation driven -->
<!-- ******************************************************************** -->
<tx:annotation-driven transaction-manager="transactionManagerReadOnly" />
<tx:annotation-driven transaction-manager="transactionManagerWriteOnly" />
<!-- ******************************************************************** -->
<!-- Setup the transaction manager -->
<!-- ******************************************************************** -->
<bean id="transactionManagerReadOnly" class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="entityManagerFactoryReadOnly" />
</bean>
<bean id="transactionManagerWriteOnly" class="org.springframework.orm.jpa.JpaTransactionManager">
<property name="entityManagerFactory" ref="entityManagerFactoryWriteOnly" />
</bean>
</beans>
My DAO:
我的道：
package com.demo.dao;
import java.util.Collections;
import java.util.List;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Repository;
import org.springframework.transaction.annotation.Transactional;
import com.demo.domain.Contact;
//import java.util.Collections;
@Repository("ContactDAO")
@Transactional
public class ContactDAOImpl extends AppDAOimpl<Contact> implements ContactDAO {
/**
*
*/
private static final long serialVersionUID = 3986253823316728444L;
/**
* EntityManager injected by Spring for persistence unit MYSQL
*
*/
@PersistenceContext(unitName = "readOnly")
@Qualifier("entityManagerFactoryReadOnly")
private EntityManager entityManager;
/**
* Get the entity manager that manages persistence unit MYSQL
*
*/
public EntityManager getEntityManager() {
return entityManager;
}
/**
* EntityManager injected by Spring for persistence unit MYSQL
*
*/
@PersistenceContext(unitName = "writeOnly")
@Qualifier("entityManagerFactoryWriteOnly")
private EntityManager woEntityManager;
/**
* Get the entity manager that manages persistence unit MYSQL
*
*/
public EntityManager getWoEntityManager() {
return woEntityManager;
}
// other functions goes here
}
Both the databases have the same schema ( read & write ).
两个数据库都具有相同的架构（读取和写入）。
采纳答案by anasanjaria
JTA transaction manager. is answer to my question. Below are links for references.
& here is nice tutorial about integrating JTA with spring.
& 这里是关于将 JTA 与 spring 集成的很好的教程。
回答by Zeus
Add two classes
添加两个类
ContactWrite.javaon top declare the schema and table like below
顶部的ContactWrite.java声明架构和表，如下所示
@Table(name = "Contact", schema="DB1")
@Table(name = "Contact", schema="DB1")
Do the same for the other table in the DB2
对 DB2 中的另一个表执行相同操作
ContactRead.java
联系人阅读.java
@Table(name = "Contact", schema="DB2")
@Table(name = "Contact", schema="DB2")
Now use these two classes in the persistance xml files like below.
现在在持久性 xml 文件中使用这两个类，如下所示。
persistent.read.only.xml:
持久性.read.only.xml：
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"
xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
<persistence-unit name="readOnly" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<class>com.demo.domain.ContactWrite</class>
</persistence-unit>
</persistence>
persistent.write.only.xml:
持久化.write.only.xml：
<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0"
xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
<persistence-unit name="writeOnly" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<class>com.demo.domain.ContactRead</class>
</persistence-unit>
</persistence>
回答by wallenborn
We have a similar setup in a project here, and I think
我们在这里的一个项目中有类似的设置，我认为
@PersistenceContext(unitName = "writeOnly")
private EntityManager woEntityManager;
is sufficient, you don't need the additional Qualifier. But in my experience, you have to set the attribute on Transactional, too. So drop the Transactional annotation on the DAO class and start marking individual methods with
就足够了，您不需要额外的限定符。但根据我的经验，您也必须在 Transactional 上设置属性。因此，删除 DAO 类上的 Transactional 注释并开始使用
@Transactional(value="transactionManagerReadOnly")
and i believe the tx:annotation-driven element in the context doesn't work with multiple contexts, too.
而且我相信上下文中的 tx:annotation-driven 元素也不适用于多个上下文。
And ideally, the whole stuff belongs into the service layer anyway, you don't want your DAOs to decide or even know which Persistence context they're called from. So you'd have a ReadContactService:
理想情况下，无论如何，所有内容都属于服务层，您不希望您的 DAO 决定甚至不知道它们是从哪个持久性上下文调用的。所以你有一个 ReadContactService：
@PersistenceContext(unitName = "readOnly")
private EntityManager em;
@Transactional(value="transactionManagerReadOnly")
public Contact readContact(int id) {
return dao.findById(em, id);
}
and a WriteContactService:
和一个 WriteContactService：
@PersistenceContext(unitName = "writeOnly")
private EntityManager em;
@Transactional(value="transactionManagerWriteOnly")
public void writeContact(String name, String address) {
return dao.writeContact(em, name, address);
}
and a DAO that is unaware of the context. Then you need only N entity classes and you can reuse DAO methods (even writeOnly will eventually have to read from the database, trust me).
以及一个不知道上下文的 DAO。那么你只需要 N 个实体类并且你可以重用 DAO 方法（即使 writeOnly 最终也必须从数据库中读取，相信我）。
