只读副本和Spring Data第4部分：配置只读存储库

以前，我们在同一应用程序中设置了两个EntityManager。一种用于读取，另一种用于写入。现在是时候创建我们的读取存储库了。

只读存储库将使用辅助只读EntityManager。

为了使其成为只读存储库，至关重要的是不要执行任何保存和持久操作。

 package com.gkatzioura.springdatareadreplica.repository;  import java.util.List;  import org.springframework.data.repository.Repository;  import com.gkatzioura.springdatareadreplica.config.ReadOnlyRepository;  import com.gkatzioura.springdatareadreplica.entity.Employee;  /** * This is a read only repository */  public interface ReadEmployeeRepository extends Repository { List findAll();  }

我们的下一个任务是使用读取数据库实体管理器创建此存储库。
这意味着除只读存储库外，所有存储库均应使用默认实体管理器创建。

我将首先创建一个注释。此注释将声明我的存储库为只读。另外，我将使用此批注进行扫描操作，以便使用适当的EntityManager。

 package com.gkatzioura.springdatareadreplica.config;  import java.lang.annotation.Documented;  import java.lang.annotation.ElementType;  import java.lang.annotation.Retention;  import java.lang.annotation.RetentionPolicy;  import java.lang.annotation.Target;  @Retention (RetentionPolicy.RUNTIME)  @Target ({ElementType.TYPE})  @Documented  public @interface ReadOnlyRepository {  }

现在，我知道Spring Boot消除了对注释的需求，并以自动化的方式创建了存储库，但是我们的案例很特殊。

通过进行一些调整，我们的只读存储库将如下所示

 package com.gkatzioura.springdatareadreplica.repository;  import java.util.List;  import org.springframework.data.repository.Repository;  import com.gkatzioura.springdatareadreplica.config.ReadOnlyRepository;  import com.gkatzioura.springdatareadreplica.entity.Employee;  /** * This is a read only repository */  @ReadOnlyRepository  public interface ReadEmployeeRepository extends Repository { List findAll();  }

现在是时候使用我们的存储库扫描了。除使用@ReadOnlyRepository批注进行注释的存储库外，所有存储库均将注入主EntityManager。

 package com.gkatzioura.springdatareadreplica.config;  import javax.sql.DataSource;  import org.springframework.beans.factory.annotation.Qualifier;  import org.springframework.beans.factory.annotation.Value;  import org.springframework.boot.jdbc.DataSourceBuilder;  import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;  import org.springframework.context.annotation.Bean;  import org.springframework.context.annotation.ComponentScan;  import org.springframework.context.annotation.Configuration;  import org.springframework.context.annotation.Primary;  import org.springframework.data.jpa.repository.config.EnableJpaRepositories;  import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;  @Configuration  @EnableJpaRepositories ( basePackages = "com.gkatzioura" , excludeFilters = @ComponentScan .Filter(ReadOnlyRepository. class ), entityManagerFactoryRef = "entityManagerFactory"  )  public class PrimaryEntityManagerConfiguration { @Value ( "${spring.datasource.username}" ) private String username; @Value ( "${spring.datasource.password}" ) private String password; @Value ( "${spring.datasource.url}" ) private String url; @Bean @Primary public DataSource dataSource() throws Exception { return DataSourceBuilder.create() .url(url) .username(username) .password(password) .driverClassName( "org.postgresql.Driver" ) .build(); } @Bean @Primary public LocalContainerEntityManagerFactoryBean entityManagerFactory( EntityManagerFactoryBuilder builder, @Qualifier ( "dataSource" ) DataSource dataSource) { return builder.dataSource(dataSource) .packages( "com.gkatzioura.springdatareadreplica" ) .persistenceUnit( "main" ) .build(); }  }

同样，我们将为只读存储库添加配置。

 package com.gkatzioura.springdatareadreplica.config;  import javax.sql.DataSource;  import org.springframework.beans.factory.annotation.Qualifier;  import org.springframework.beans.factory.annotation.Value;  import org.springframework.boot.jdbc.DataSourceBuilder;  import org.springframework.boot.orm.jpa.EntityManagerFactoryBuilder;  import org.springframework.context.annotation.Bean;  import org.springframework.context.annotation.ComponentScan;  import org.springframework.context.annotation.Configuration;  import org.springframework.data.jpa.repository.config.EnableJpaRepositories;  import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;  @Configuration  @EnableJpaRepositories ( basePackages = "com.gkatzioura" , includeFilters= @ComponentScan .Filter(ReadOnlyRepository. class ), entityManagerFactoryRef = "readEntityManagerFactory"  )  public class ReadOnlyEntityManagerConfiguration { @Value ( "${spring.datasource.username}" ) private String username; @Value ( "${spring.datasource.password}" ) private String password; @Value ( "${spring.datasource.readUrl}" ) private String readUrl; @Bean public DataSource readDataSource() throws Exception { return DataSourceBuilder.create() .url(readUrl) .username(username) .password(password) .driverClassName( "org.postgresql.Driver" ) .build(); } @Bean public LocalContainerEntityManagerFactoryBean readEntityManagerFactory( EntityManagerFactoryBuilder builder, @Qualifier ( "readDataSource" ) DataSource dataSource) { return builder.dataSource(dataSource) .packages( "com.gkatzioura.springdatareadreplica" ) .persistenceUnit( "read" ) .build(); }  }

辅助实体管理器将仅注入仅具有@ReadOnlyRepository批注的存储库。

为了说明这一点，让我们对控制器进行一些更改。

 package com.gkatzioura.springdatareadreplica.controller;  import java.util.List;  import org.springframework.http.HttpStatus;  import org.springframework.web.bind.annotation.GetMapping;  import org.springframework.web.bind.annotation.PostMapping;  import org.springframework.web.bind.annotation.RequestBody;  import org.springframework.web.bind.annotation.ResponseStatus;  import org.springframework.web.bind.annotation.RestController;  import com.gkatzioura.springdatareadreplica.entity.Employee;  import com.gkatzioura.springdatareadreplica.repository.EmployeeRepository;  import com.gkatzioura.springdatareadreplica.repository.ReadEmployeeRepository;  @RestController  public class EmployeeContoller { private final EmployeeRepository employeeRepository; private final ReadEmployeeRepository readEmployeeRepository; public EmployeeContoller(EmployeeRepository employeeRepository, ReadEmployeeRepository readEmployeeRepository) { this .employeeRepository = employeeRepository; this .readEmployeeRepository = readEmployeeRepository; } @GetMapping ( "/employee" ) public List getEmployees() { return employeeRepository.findAll(); } @GetMapping ( "/employee/read" ) public List getEmployeesRead() { return readEmployeeRepository.findAll(); } @PostMapping ( "/employee" ) @ResponseStatus (HttpStatus.CREATED) @ResponseStatus (HttpStatus.CREATED) public void addEmployee( @RequestBody Employee employee) { employeeRepository.save(employee); }  }

当您将员工添加到系统时，只读存储库将继续获取旧员工，而主存储库将获取所有员工，包括最近保留的员工。