Verwenden mehrerer DataSource mit Spring Boot und JPA

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1- Das Zweck des Artikel

Der Artikel wird nach ... geschrieben
  • Spring Boot 2.x (or >=1.5.9)

  • JPA

  • Thymeleaf (Or JSP)

Im Artikel leite ich Sie bei der Erstellung einer Applikation  Spring Boot & JPA mit der Verwendung von vielen  DataSource. Wir haben 2 Database um mit dem Beispiel durchzuführen
  • PUBLISHER: Das ist die Database 1, die eine Tabelle PUBLISHERS hat.
  • ADVERTISER: Das ist die Database 2, die eine Tabelle ADVERTISERS hat.
In der Applikation können gleichzeitig 2 obengemeinten Database verwenden. Zum Beispiel eine Seite zeigt die Liste der Publisher und gleichzeitig die Liste der Advertiser an. Deshalb sollen Sie mit 2 obengemeinten Database gleichzeitig arbeiten.
Im anderen Fall wenn Ihre Applikation mehr  DataSource braucht, aber arbeitet in jeder Funktion (jeder Seite) nur mit einer bestimmten  DataSource , dann sollen Sie  Routing DataSource & DataSource Interceptor verwenden.
  1. Routing DataSource ist eine besondere DataSource. Sie enthaltet die Liste von DataSource , die in Ihrer Applikation verwendet werden.
  2. DataSource Interceptor wird entscheiden, welche DataSource nach der entsprechenden Funktion (jede Seite) in Ihrer Applikation verwendet werden

2- Database vorbereiten

MySQL, SQL Server, PostGres
-- ===========================================
-- DATABASE FOR PUBLISHER SYSTEM
-- ===========================================
create table PUBLISHERS
(
  ID Bigint,
  NAME VARCHAR(255),
  Primary key (ID)
);

insert into publishers (ID, NAME)
values (1, 'publisher 1');

insert into publishers (ID, NAME)
values (2, 'publisher 2');



-- ===========================================
-- DATABASE FOR ADVERTISER SYSTEM
-- ===========================================
create table ADVERTISERS
(
  ID Bigint,
  NAME VARCHAR(255),
  Primary key (ID)
);

insert into advertisers (ID, NAME)
values (1, 'Advertiser 1');

insert into advertisers (ID, NAME)
values (2, 'Advertiser 2');
Oracle
-- ===========================================
-- DATABASE FOR PUBLISHER SYSTEM
-- ===========================================
create table PUBLISHERS
(
  ID NUMBER(19),
  NAME VARCHAR(255),
  Primary key (ID)
);

insert into publishers (ID, NAME)
values (1, 'publisher 1');

insert into publishers (ID, NAME)
values (2, 'publisher 2');

Commit;

-- ===========================================
-- DATABASE FOR ADVERTISER SYSTEM
-- ===========================================
create table ADVERTISERS
(
  ID NUMBER(19),
  NAME VARCHAR(255),
  Primary key (ID)
);

insert into advertisers (ID, NAME)
values (1, 'Advertiser 1');

insert into advertisers (ID, NAME)
values (2, 'Advertiser 2');

Commit;

3-  Das Projekt Spring Boot erstellen

4- pom.xml konfigurieren

In die folgende  pom.xml habe ich konfiguriert, dass die Applikation mit 4 üblichen Database wie  MySQL, SQL Server, PostGres, Oracle arbeiten kann.
pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
               http://maven.apache.org/xsd/maven-4.0.0.xsd">
               
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.o7planning</groupId>
    <artifactId>SpringBootJPAMultiDS</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>SpringBootJPAMultiDS</name>
    <description>Spring Boot + JPA + Multiple DataSources</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.0.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-jpa</artifactId>
        </dependency>
        
        <!-- Remove Thymeleaf, If you want using JSP View -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-thymeleaf</artifactId>
        </dependency>
        
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.postgresql</groupId>
            <artifactId>postgresql</artifactId>
            <scope>runtime</scope>
        </dependency>
        <!-- SQL Server - Mssql-Jdbc driver -->
        <dependency>
            <groupId>com.microsoft.sqlserver</groupId>
            <artifactId>mssql-jdbc</artifactId>
            <scope>runtime</scope>
        </dependency>
        
        <!-- SQL Server - JTDS driver -->
        <dependency>
            <groupId>net.sourceforge.jtds</groupId>
            <artifactId>jtds</artifactId>
            <scope>runtime</scope>
        </dependency>
        
        <dependency>
            <groupId>com.oracle</groupId>
            <artifactId>ojdbc6</artifactId>
            <version>11.2.0.3</version>
        </dependency>
        
        
        <!-- For JSP VIEW (Need REMOVE spring-boot-starter-thymeleaf) -->
        <dependency>
            <groupId>org.apache.tomcat.embed</groupId>
            <artifactId>tomcat-embed-jasper</artifactId>
        </dependency>
        
        <!-- For JSP VIEW (Need REMOVE spring-boot-starter-thymeleaf) -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
        </dependency>
        
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <repositories>
    
        <!-- Repository for ORACLE JDBC Driver -->
        <repository>
            <id>codelds</id>
            <url>https://code.lds.org/nexus/content/groups/main-repo</url>
        </repository>
        
    </repositories>
 
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

5-  DataSource konfigurieren

datasource-cfg.properties (MySQL)
# ===============================
# DATASOURCE
# ===============================

# DataSource (PUBLISHER System).

spring.datasource.driver-class-name.1=com.mysql.jdbc.Driver
spring.datasource.url.1=jdbc:mysql://localhost:3306/publisher
spring.datasource.username.1=root
spring.datasource.password.1=12345



# DataSource (ADVERTISER System).

spring.datasource.driver-class-name.2=com.mysql.jdbc.Driver
spring.datasource.url.2=jdbc:mysql://localhost:3306/advertiser
spring.datasource.username.2=root
spring.datasource.password.2=12345



# ===============================
# JPA / HIBERNATE
# ===============================

spring.jpa.show-sql.1=true
spring.jpa.hibernate.ddl-auto.1=none
spring.jpa.properties.hibernate.dialect.1=org.hibernate.dialect.MySQLDialect
#spring.jpa.properties.hibernate.current_session_context_class.1=org.springframework.orm.hibernate5.SpringSessionContext


spring.jpa.show-sql.2=true
spring.jpa.hibernate.ddl-auto.2=none
spring.jpa.properties.hibernate.dialect.2=org.hibernate.dialect.MySQLDialect
#spring.jpa.properties.hibernate.current_session_context_class.2=org.springframework.orm.hibernate5.SpringSessionContext
 
datasource-cfg.properties (SQL Server + JTDS Driver)
# ===============================
# DATASOURCE
# ===============================


# DataSource  (PUBLISHER System).

spring.datasource.driver-class-name.1=net.sourceforge.jtds.jdbc.Driver
spring.datasource.url.1=jdbc:jtds:sqlserver://localhost:1433/publisher;instance=SQLEXPRESS
spring.datasource.username.1=sa
spring.datasource.password.1=12345


# DataSource  (ADVERTISER System).

spring.datasource.driver-class-name.2=net.sourceforge.jtds.jdbc.Driver
spring.datasource.url.2=jdbc:jtds:sqlserver://localhost:1433/advertiser;instance=SQLEXPRESS
spring.datasource.username.2=sa
spring.datasource.password.2=12345



# ===============================
# JPA / HIBERNATE
# ===============================

spring.jpa.show-sql.1=true
spring.jpa.hibernate.ddl-auto.1=none
spring.jpa.properties.hibernate.dialect.1=org.hibernate.dialect.SQLServerDialect
#spring.jpa.properties.hibernate.current_session_context_class.1=org.springframework.orm.hibernate5.SpringSessionContext


spring.jpa.show-sql.2=true
spring.jpa.hibernate.ddl-auto.2=none
spring.jpa.properties.hibernate.dialect.2=org.hibernate.dialect.SQLServerDialect
#spring.jpa.properties.hibernate.current_session_context_class.2=org.springframework.orm.hibernate5.SpringSessionContext
datasource-cfg.properties (SQL Server + Mssql-Jdbc Driver)
# ===============================
# DATASOURCE
# ===============================


# DataSource  (PUBLISHER System).

spring.datasource.driver-class-name.1=com.microsoft.sqlserver.jdbc.SQLServerDriver
spring.datasource.url.1=jdbc:sqlserver://tran-vmware-pc\\SQLEXPRESS:1433;databaseName=publisher
spring.datasource.username.1=sa
spring.datasource.password.1=12345


# DataSource  (ADVERTISER System).

spring.datasource.driver-class-name.2=com.microsoft.sqlserver.jdbc.SQLServerDriver
spring.datasource.url.2=jdbc:sqlserver://tran-vmware-pc\\SQLEXPRESS:1433;databaseName=advertiser
spring.datasource.username.2=sa
spring.datasource.password.2=12345


# ===============================
# JPA / HIBERNATE
# ===============================

spring.jpa.show-sql.1=true
spring.jpa.hibernate.ddl-auto.1=none
spring.jpa.properties.hibernate.dialect.1=org.hibernate.dialect.SQLServerDialect
#spring.jpa.properties.hibernate.current_session_context_class.1=org.springframework.orm.hibernate5.SpringSessionContext


spring.jpa.show-sql.2=true
spring.jpa.hibernate.ddl-auto.2=none
spring.jpa.properties.hibernate.dialect.2=org.hibernate.dialect.SQLServerDialect
#spring.jpa.properties.hibernate.current_session_context_class.2=org.springframework.orm.hibernate5.SpringSessionContext
 
datasource-cfg.properties (Oracle)
# ===============================
# DATASOURCE
# ===============================

# DataSource (PUBLISHER System).

spring.datasource.driver-class-name.1=oracle.jdbc.driver.OracleDriver
spring.datasource.url.1=jdbc:oracle:thin:@localhost:1521:db12c
spring.datasource.username.1=publisher
spring.datasource.password.1=12345


# DataSource (ADVERTISER System).

spring.datasource.driver-class-name.2=oracle.jdbc.driver.OracleDriver
spring.datasource.url.2=jdbc:oracle:thin:@localhost:1521:db12c
spring.datasource.username.2=advertiser
spring.datasource.password.2=12345



# ===============================
# JPA / HIBERNATE
# ===============================

spring.jpa.show-sql.1=true
spring.jpa.hibernate.ddl-auto.1=none
spring.jpa.properties.hibernate.dialect.1=org.hibernate.dialect.Oracle10gDialect
#spring.jpa.properties.hibernate.current_session_context_class.1=org.springframework.orm.hibernate5.SpringSessionContext


spring.jpa.show-sql.2=true
spring.jpa.hibernate.ddl-auto.2=none
spring.jpa.properties.hibernate.dialect.2=org.hibernate.dialect.Oracle10gDialect
#spring.jpa.properties.hibernate.current_session_context_class.2=org.springframework.orm.hibernate5.SpringSessionConte
datasource-cfg.properties (PostGres)
# ===============================
# DATASOURCE
# ===============================

# DataSource (PUBLISHER System).

spring.datasource.driver-class-name.1=org.postgresql.Driver
spring.datasource.url.1=jdbc:postgresql://tran-vmware-pc:5432/publisher
spring.datasource.username.1=postgres
spring.datasource.password.1=12345



# DataSource (ADVERTISER System).

spring.datasource.driver-class-name.2=org.postgresql.Driver
spring.datasource.url.2=jdbc:postgresql://tran-vmware-pc:5432/advertiser
spring.datasource.username.2=postgres
spring.datasource.password.2=12345



# ===============================
# JPA / HIBERNATE
# ===============================

spring.jpa.show-sql.1=true
spring.jpa.hibernate.ddl-auto.1=none
spring.jpa.properties.hibernate.dialect.1=org.hibernate.dialect.PostgreSQL9Dialect
#spring.jpa.properties.hibernate.current_session_context_class.1=org.springframework.orm.hibernate5.SpringSessionContext


spring.jpa.show-sql.2=true
spring.jpa.hibernate.ddl-auto.2=none
spring.jpa.properties.hibernate.dialect.2=org.hibernate.dialect.PostgreSQL9Dialect
#spring.jpa.properties.hibernate.current_session_context_class.2=org.springframework.orm.hibernate5.SpringSessionContext

 
Nach dem Standard wird  Spring Boot eine standardmäßige  DataSource automatisch konfigurieren. Deshalb brauchen Sie die automatische Konfiguration vom  Spring Boot deaktivieren und machen Ihre eigenen Konfiguration vom  DataSource 
SpringBootJPAMultiDsApplication.java
package org.o7planning.sbmultids;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;
import org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration;
import org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration;

@SpringBootApplication

// Disable some Spring Boot auto config
@EnableAutoConfiguration(exclude = { //
        DataSourceAutoConfiguration.class, //
        DataSourceTransactionManagerAutoConfiguration.class, //
        HibernateJpaAutoConfiguration.class })

public class SpringBootJPAMultiDsApplication {

    public static void main(String[] args) {
        SpringApplication.run(SpringBootJPAMultiDsApplication.class, args);
    }
    
}
Zunächst werden wir 2 DataSource konfigurieren:
  1. Die Klasse DataSource1Config für die Konfiguration von Datasource 1 (PUBLISHER DB).
  2. Die Klasse DataSource2Config für die Konfiguration von Datasource 2 (ADVERTISER DB).
Constants.java
package org.o7planning.sbmultids.config;

public class Constants {
    
    public static final String PACKAGE_ENTITIES_1 = "org.o7planning.sbmultids.entity1";
    
    public static final String PACKAGE_ENTITIES_2 = "org.o7planning.sbmultids.entity2";
    
    public static final String JPA_UNIT_NAME_1 ="PERSITENCE_UNIT_NAME_1";
    public static final String JPA_UNIT_NAME_2 ="PERSITENCE_UNIT_NAME_2";
    
}
DataSource1Config.java
package org.o7planning.sbmultids.config;

import java.util.HashMap;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.context.annotation.PropertySources;
import org.springframework.core.env.Environment;
import org.springframework.jdbc.datasource.DriverManagerDataSource;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
import org.springframework.transaction.PlatformTransactionManager;

@Configuration
// Load to Environment
// (@see resources/datasource-cfg.properties).
@PropertySources({ @PropertySource("classpath:datasource-cfg.properties") })
public class DataSource1Config {

    @Autowired
    private Environment env; // Contains Properties Load by @PropertySources

    @Bean
    public DataSource ds1Datasource() {

        DriverManagerDataSource dataSource = new DriverManagerDataSource();
        dataSource.setDriverClassName(env.getProperty("spring.datasource.driver-class-name.1"));
        dataSource.setUrl(env.getProperty("spring.datasource.url.1"));
        dataSource.setUsername(env.getProperty("spring.datasource.username.1"));
        dataSource.setPassword(env.getProperty("spring.datasource.password.1"));

        return dataSource;
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean ds1EntityManager() {
        LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();
        em.setDataSource(ds1Datasource());

        // Scan Entities in Package:
        em.setPackagesToScan(new String[] { Constants.PACKAGE_ENTITIES_1 });
        em.setPersistenceUnitName(Constants.JPA_UNIT_NAME_1); // Important !!

        //
        HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();

        em.setJpaVendorAdapter(vendorAdapter);

        HashMap<String, Object> properties = new HashMap<>();

        // JPA & Hibernate
        properties.put("hibernate.dialect", env.getProperty("spring.jpa.properties.hibernate.dialect.1"));
        properties.put("hibernate.show-sql", env.getProperty("spring.jpa.show-sql.1"));

        // Solved Error: PostGres createClob() is not yet implemented.
        // PostGres Only:
        // properties.put("hibernate.temp.use_jdbc_metadata_defaults",  false);

        em.setJpaPropertyMap(properties);
        em.afterPropertiesSet();
        return em;
    }

    @Bean
    public PlatformTransactionManager ds1TransactionManager() {

        JpaTransactionManager transactionManager = new JpaTransactionManager();
        transactionManager.setEntityManagerFactory(ds1EntityManager().getObject());
        return transactionManager;
    }

}
DataSource2Config.java
package org.o7planning.sbmultids.config;

import java.util.HashMap;

import javax.sql.DataSource;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.PropertySource;
import org.springframework.context.annotation.PropertySources;
import org.springframework.core.env.Environment;
import org.springframework.jdbc.datasource.DriverManagerDataSource;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
import org.springframework.transaction.PlatformTransactionManager;

@Configuration
// Load to Environment
// (@see resources/datasource-cfg.properties).
@PropertySources({ @PropertySource("classpath:datasource-cfg.properties") })
public class DataSource2Config {

    @Autowired
    private Environment env; // Contains Properties Load by @PropertySources

    @Bean
    public DataSource ds2Datasource() {
        DriverManagerDataSource dataSource = new DriverManagerDataSource();

        dataSource.setDriverClassName(env.getProperty("spring.datasource.driver-class-name.2"));
        dataSource.setUrl(env.getProperty("spring.datasource.url.2"));
        dataSource.setUsername(env.getProperty("spring.datasource.username.2"));
        dataSource.setPassword(env.getProperty("spring.datasource.password.2"));

        return dataSource;
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean ds2EntityManager() {
        LocalContainerEntityManagerFactoryBean em = new LocalContainerEntityManagerFactoryBean();
        em.setDataSource(ds2Datasource());

        // Scan Entities in Package:
        em.setPackagesToScan(new String[] { Constants.PACKAGE_ENTITIES_2 });

        em.setPersistenceUnitName(Constants.JPA_UNIT_NAME_2);
        HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
        em.setJpaVendorAdapter(vendorAdapter);

        HashMap<String, Object> properties = new HashMap<>();
        // JPA & Hibernate
        properties.put("hibernate.dialect", env.getProperty("spring.jpa.properties.hibernate.dialect.2"));
        properties.put("hibernate.show-sql", env.getProperty("spring.jpa.show-sql.2"));

        // Solved Error: PostGres createClob() is not yet implemented.
        // PostGres Only.
        // properties.put("hibernate.temp.use_jdbc_metadata_defaults",  false);

        em.setJpaPropertyMap(properties);
        em.afterPropertiesSet();
        return em;
    }

    @Bean
    public PlatformTransactionManager ds2TransactionManager() {

        JpaTransactionManager transactionManager = new JpaTransactionManager();
        transactionManager.setEntityManagerFactory(ds2EntityManager().getObject());
        return transactionManager;
    }

}

6- Entities, DAO

Publisher.java
package org.o7planning.sbmultids.entity1;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "Publishers")
public class Publisher implements Serializable {

    private static final long serialVersionUID = 746237126088051312L;

    @Id
    @GeneratedValue
    @Column(name = "Id")
    private Long id;

    @Column(name = "Name", length = 255, nullable = false)
    private String name;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}
Advertiser.java
package org.o7planning.sbmultids.entity2;

import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.Id;
import javax.persistence.Table;

@Entity
@Table(name = "Advertisers")
public class Advertiser implements Serializable {

    private static final long serialVersionUID = 746237126088051312L;

    @Id
    @GeneratedValue
    @Column(name = "Id")
    private Long id;

    @Column(name = "Name", length = 255, nullable = false)
    private String name;

    public Long getId() {
        return id;
    }

    public void setId(Long id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}
PublisherDAO.java
package org.o7planning.sbmultids.dao;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;

import org.o7planning.sbmultids.config.Constants;
import org.o7planning.sbmultids.entity1.Publisher;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;

@Repository
public class PublisherDAO {

    @Autowired
    @PersistenceContext( unitName= Constants.JPA_UNIT_NAME_1)
    private EntityManager entityManager;

    public List<Publisher> listPublishers() {
        String sql = "Select e from " + Publisher.class.getName() + " e ";
        Query query = entityManager.createQuery(sql, Publisher.class);
        return query.getResultList();
    }

    public Publisher findById(Long id) {
        return this.entityManager.find(Publisher.class, id);
    }
    
}
AdvertiserDAO.java
package org.o7planning.sbmultids.dao;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;

import org.o7planning.sbmultids.config.Constants;
import org.o7planning.sbmultids.entity2.Advertiser;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;

@Repository
public class AdvertiserDAO {
 

    @Autowired
    @PersistenceContext(unitName = Constants.JPA_UNIT_NAME_2)
    private EntityManager entityManager;

    public List<Advertiser> listAdvertisers() {
        String sql = "Select e from " + Advertiser.class.getName() + " e ";
        Query query = entityManager.createQuery(sql, Advertiser.class);
        return query.getResultList();
    }

    public Advertiser findById(Long id) {
        return this.entityManager.find(Advertiser.class, id);
    }
    
}

7- Controller

MainController.java
package org.o7planning.sbmultids.controller;

import java.util.List;

import org.o7planning.sbmultids.dao.AdvertiserDAO;
import org.o7planning.sbmultids.dao.PublisherDAO;
import org.o7planning.sbmultids.entity1.Publisher;
import org.o7planning.sbmultids.entity2.Advertiser;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
public class MainController {

    @Autowired
    private PublisherDAO publisherDAO;

    @Autowired
    private AdvertiserDAO advertiserDAO;

    @RequestMapping(value = "/", method = RequestMethod.GET)
    public String homePage(Model model) {

        List<Advertiser> advertisers = advertiserDAO.listAdvertisers();
        List<Publisher> publishers = publisherDAO.listPublishers();

        model.addAttribute("advertisers", advertisers);
        model.addAttribute("publishers", publishers);

        return "home";
    }

}

8- Thymeleaf Template

home.html
<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8"/>
      <title>Home</title>
      <style>
        th, td {
          padding: 5px;
        }
        table  {
           border-collapse: collapse;
        }
      
      </style>
   </head>
   
   <body>
      
      <h3>Using Publisher-DB</h3>
      
      <table border="1">
        <tr>
           <th>ID</th>
           <th>Name</th>
        </tr>
        <tr th:each="publisher : ${publishers}">
           <td th:utext="${publisher.id}"></td>
           <td th:utext="${publisher.name}"></td>
        </tr>
      </table>
      
      <h3>Using Advertiser-DB</h3>
      
      <table border="1">
        <tr>
           <th>ID</th>
           <th>Name</th>
        </tr>
        <tr th:each="advertiser : ${advertisers}">
           <td th:utext="${advertiser.id}"></td>
           <td th:utext="${advertiser.name}"></td>
        </tr>
      </table>
     
      
   </body>
   
</html>

9- Der Anhang: JSP View

Mehr sehen
Falls Sie die Technologie  JSP für  View-Layer verwenden:
home.jsp
<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>
<%@ page contentType="text/html; charset=UTF-8" %>

<!DOCTYPE html>
<html xmlns:th="http://www.thymeleaf.org">
   <head>
      <meta charset="UTF-8"/>
      <title>Home</title>
      <style>
        th, td {
          padding: 5px;
        }
        table  {
           border-collapse: collapse;
        }
      
      </style>
   </head>
   
   <body>
      
      <h3>Using Publisher-DB</h3>
      
      <table border="1">
        <tr>
           <th>ID</th>
           <th>Name</th>
        </tr>
        <c:forEach items="${publishers}" var="publisher">
            <tr>
               <td th:utext="${publisher.id}"></td>
               <td th:utext="${publisher.name}"></td>
            </tr>
        </c:forEach>
      </table>
      
      <h3>Using Advertiser-DB</h3>
      
      <table border="1">
        <tr>
           <th>ID</th>
           <th>Name</th>
        </tr>
        <c:forEach items="${advertisers}" var="advertiser">
            <tr>
               <td th:utext="${advertiser.id}"></td>
               <td th:utext="${advertiser.name}"></td>
            </tr>
        </c:forEach>
      </table>
     
      
   </body>
   
</html>

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