Spring Boot 应用系列 1 -- Spring Boot 2 整合Spring Data JPA和Druid，双数据源

最近Team开始尝试使用Spring Boot + Spring Data JPA作为数据层的解决方案，在网上逛了几圈之后发现大家并不待见JPA，理由是(1)MyBatis简单直观够用，(2)以Hibernate为底层的Spring Data JPA复杂且性能一般。

但是当我们来到Spring Boot的世界后发现，相较于Spring Data JPA，MyBatis对Spring Boot的支持有限，Spring Data JPA与Spring Boot结合可以让dao变得非常简单，比如(1)JPA自带分页对象，无需设置插件；(2)一个空接口搞定所有基本CRUD。

本着虚心学习的态度，我决定将Spring Boot、Spring Data JPA和Druid三者整合在一起，并分别对SQL Server和MySQL进行支持，希望本文能够帮助到需要相关技术的同学。

1. 程序和版本

Spring Boot 2.0.4

mssql-jdbc 6.2.2.jre8

mysql-connector-java 5.1.46

druid-spring-boot-starter 1.1.10

2. properties配置文件

我们把主程序配置文件application.properties和数据库配置文件分开，这样可使application.properties不至于臃肿。

(1) application.properties

 server.port=
 spring.application.name=spring-data-jpa

 #Serialize JPA entity to Json string.
 spring.jackson.serialization.fail-on-empty-beans=false

第5行的作用是避免com.fasterxml.jackson.databind.exc.InvalidDefinitionException: No serializer found for class org.hibernate.proxy.pojo.javassist.JavassistLazyInitializer and no properties discovered to create BeanSerializer，该配置只对MSSQL数据源有效。

(2) db.properties

 #Data source
 db1.sqlserver.driver-class-name=com.microsoft.sqlserver.jdbc.SQLServerDriver
 db1.sqlserver.url=${DB1_URL:jdbc:sqlserver://127.0.0.1:1433;DatabaseName=MyTestDb1}
 db1.sqlserver.username=${DB1_UID:tester}
 db1.sqlserver.password=${DB1_PWD:tester}
 
 6 db1.sqlserver.initial-size=
 db1.sqlserver.min-idle=
 db1.sqlserver.max-active=
 db1.sqlserver.max-wait=
 db1.sqlserver.time-between-eviction-runs-millis=
 db1.sqlserver.min-evictable-idle-time-millis=
 db1.sqlserver.validation-query=select
 db1.sqlserver.test-on-borrow=true
 db1.sqlserver.test-While-Idle=true
 db1.sqlserver.test-on-return=false
 db1.sqlserver.pool-prepared-statements=false
 db1.sqlserver.max-pool-prepared-statement-per-connection-size=

 db1.sqlserver.filter.stat.enabled=true
 db1.sqlserver.filter.stat.db-type=mssql
 db1.sqlserver.filter.stat.log-slow-sql=true
 db1.sqlserver.filter.stat.slow-sql-millis=

 db1.sqlserver.jpa.hibernate.dialect=org.hibernate.dialect.SQLServerDialect
 db1.sqlserver.jpa.hibernate.show_sql=true
 db1.sqlserver.jpa.hibernate.format_sql=true

 #Data source
 db2.mysql.driver-class-name=com.mysql.jdbc.Driver
 db2.mysql.url=${DB2_URL:jdbc:mysql://127.0.0.1:3306/Test}?useUnicode=true&useSSL=false
 db2.mysql.username=${DB2_UID:tester}
 db2.mysql.password=${DB2_PWD:tester}
 db2.mysql.initial-size=
 db2.mysql.min-idle=
 db2.mysql.max-active=
 db2.mysql.max-wait=
 db2.mysql.time-between-eviction-runs-millis=
 db2.mysql.min-evictable-idle-time-millis=
 db2.mysql.validation-query=select
 db2.mysql.test-on-borrow=true
 db2.mysql.test-While-Idle=true
 db2.mysql.test-on-return=false
 db2.mysql.pool-prepared-statements=false
 db2.mysql.max-pool-prepared-statement-per-connection-size=

 db2.mysql.filter.stat.enabled=true
 db2.mysql.filter.stat.db-type=mysql
 db2.mysql.filter.stat.log-slow-sql=true
 db2.mysql.filter.stat.slow-sql-millis=

 db2.mysql.jpa.hibernate.dialect=org.hibernate.dialect.MySQLDialect
 db2.mysql.jpa.hibernate.show_sql=true
 db2.mysql.jpa.hibernate.format_sql=true
 db2.mysql.jpa.hibernate.enable_lazy_load_no_trans=true

该配置文件可分为三部分：一是JPA的数据源基本信息配置（行5之前）；二是JPA的数据库连接池配置（行6-行17）；三是Druid连接池的特殊配置（行19-行22）；四是自定义配置（行24-行26）。

需要注意行54的配置，加这一行是为了解决由Hibernate懒加载引起的异常org.hibernate.LazyInitializationException: could not initialize proxy [devutility.test.database.springdatajpa.dao.mysql.entity.Customer#100000123] - no Session

但是让enable_lazy_load_no_trans=true会带来一定的性能问题，具体参考https://vladmihalcea.com/the-hibernate-enable_lazy_load_no_trans-anti-pattern/

此外，解决org.hibernate.LazyInitializationException异常还有另外一种方法，在每个Entity类型上添加@Proxy(lazy = false)注解，经测试有效。

3. Java Config

为便于管理，每个数据源一个配置类，此处只列出一个数据源：

 import java.util.Properties;

 import javax.sql.DataSource;

 import org.springframework.boot.context.properties.ConfigurationProperties;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.context.annotation.Primary;
 import org.springframework.context.annotation.PropertySource;
 import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
 import org.springframework.orm.jpa.JpaTransactionManager;
 import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
 import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
 import org.springframework.transaction.PlatformTransactionManager;

 import com.alibaba.druid.spring.boot.autoconfigure.DruidDataSourceBuilder;

 import devutility.internal.util.PropertiesUtils;

 @Configuration
 @PropertySource("classpath:db.properties")
 @EnableJpaRepositories(basePackages = "devutility.test.database.springdatajpa.dao.mssql", entityManagerFactoryRef = "entityManagerFactory1", transactionManagerRef = "transactionManager1")
 public class DataSource1Configuration {
     @Primary
     @Bean
     @ConfigurationProperties("db1.sqlserver")
     public DataSource dataSource1() {
         return DruidDataSourceBuilder.create().build();
     }

     @Bean
     @ConfigurationProperties("db1.sqlserver.jpa")
     public Properties jpaProperties1() {
         return new Properties();
     }

     @Primary
     @Bean
     public LocalContainerEntityManagerFactoryBean entityManagerFactory1() {
         LocalContainerEntityManagerFactoryBean localContainerEntityManagerFactoryBean = new LocalContainerEntityManagerFactoryBean();
         localContainerEntityManagerFactoryBean.setDataSource(dataSource1());
         localContainerEntityManagerFactoryBean.setPackagesToScan(new String[] { "devutility.test.database.springdatajpa.dao.mssql.entity" });
         localContainerEntityManagerFactoryBean.setJpaVendorAdapter(new HibernateJpaVendorAdapter());
         localContainerEntityManagerFactoryBean.setJpaPropertyMap(PropertiesUtils.toMap(jpaProperties1()));
         return localContainerEntityManagerFactoryBean;
     }

     @Bean
     public PlatformTransactionManager transactionManager1() {
         JpaTransactionManager transactionManager = new JpaTransactionManager();
         transactionManager.setEntityManagerFactory(entityManagerFactory1().getObject());
         return transactionManager;
     }
 }

4. Druid控制台页面配置

Druid的详细配置见Druid官网

如果你不想对Druid控制台的访问加以限制可以忽略此节，如果你希望通过用户名和密码访问Druid控制台，有如下两种配置方式：

(1)Java Config

import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import com.alibaba.druid.support.http.StatViewServlet;
import com.alibaba.druid.support.http.WebStatFilter;

@Configuration
public class DruidConfiguration {
    @Bean
    public ServletRegistrationBean<StatViewServlet> druidStatViewServlet() {
        ServletRegistrationBean<StatViewServlet> servletRegistrationBean = new ServletRegistrationBean<>(new StatViewServlet(), "/druid/*");
        servletRegistrationBean.addInitParameter("loginUsername", "admin");
        servletRegistrationBean.addInitParameter("loginPassword", "admin");
        servletRegistrationBean.addInitParameter("resetEnable", "false");
        return servletRegistrationBean;
    }

    @Bean
    public FilterRegistrationBean<WebStatFilter> druidStatFilter() {
        FilterRegistrationBean<WebStatFilter> filterRegistrationBean = new FilterRegistrationBean<>(new WebStatFilter());
        filterRegistrationBean.setName("DruidWebStatFilter");
        filterRegistrationBean.addUrlPatterns("/*");
        filterRegistrationBean.addInitParameter("exclusions", "*.js,*.gif,*.jpg,*.png,*.css,*.ico,/druid/*");
        return filterRegistrationBean;
    }
}

(2). 在application.properties文件中添加

#Configuration for druid
spring.datasource.druid.stat-view-servlet.enabled=true
spring.datasource.druid.stat-view-servlet.url-pattern=/druid/*
spring.datasource.druid.stat-view-servlet.login-username=admin
spring.datasource.druid.stat-view-servlet.login-password=admin

5. 应用

配置好之后就该实现CRUD的基本功能了：

(1) 定义一个实体类Customer

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

@Entity
@Table(name = "Customer")
public class Customer extends BaseEntity {
    @Id
    private long id;

    @Column(name = "Name1")
    private String name;

    @Column(name = "Address1")
    private String address;

    private String city;
    private int state;
    private int zip;
    private String phone;
    private String email;

这里需要注意以下几点：

a. 所有JPA的实体类都需要有@Entity的注解；

b. @Table注解可选，如果不设置则表名=类名，如果表名和类名不一致则需要配置；

c. @Column注解可选，用于表中字段名和实体类的属性不一致的情况；

d: 可在拥有@Id字段上添加@GeneratedValue注解用于生成主键。

(2) Dao层

a. 对于每一个表，只需要定义一个简单的接口并继承JpaRepository<T, ID>即可实现基本的CRUD还有分页操作：

package devutility.test.database.springdatajpa.dao.mysql;

import org.springframework.data.jpa.repository.JpaRepository;

import devutility.test.database.springdatajpa.dao.mysql.entity.Customer;

public interface CustomerRepository extends JpaRepository<Customer, Long> {

}

b. 假设你的实体类是通过联表查询得到的，或者对于一个单表来说基本的CRUD无法满足你的需求，你可以通过使用@Query注解来手写SQL语句实现，下面我们来演示一下这种情况：

首先定义一个实体类SimpleCustomer，该实体类只包含Customer的部分字段。

package devutility.test.database.springdatajpa.dao.mysql.entity;

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

@Entity
@Table(name = "Customer")
public class SimpleCustomer {
    @Id
    private long id;

    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;
    }
}

然后我们再定义SimpleCustomer对应的Repository：

package devutility.test.database.springdatajpa.dao.mysql;

import java.util.Date;
import java.util.List;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;

import devutility.test.database.springdatajpa.dao.mysql.entity.SimpleCustomer;

public interface SimpleCustomerRepository extends JpaRepository<SimpleCustomer, Long> {
    @Query(value = "select ID, Name1 Name, Address1 Address, Created from Customer where Created > ?1 and Name1 is not null order by Created desc limit ?2, ?3", nativeQuery = true)
    List<SimpleCustomer> paging(Date startDate, int skip, int pageSize);
}

在SimpleCustomerRepository中，我们定义了一个接口paging，用来进行分页查询。注意，一定要有nativeQuery = true，否则报错。

(3) 应用层

接下来就是怎样使用上面定义的Repository了:

import java.text.ParseException;
import java.util.Date;
import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;
import org.springframework.data.domain.Sort.Direction;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import devutility.internal.models.OperationResult;
import devutility.internal.text.format.DateFormatUtils;
import devutility.test.database.springdatajpa.dao.mysql.CustomerRepository;
import devutility.test.database.springdatajpa.dao.mysql.SimpleCustomerRepository;
import devutility.test.database.springdatajpa.dao.mysql.entity.Customer;
import devutility.test.database.springdatajpa.dao.mysql.entity.SimpleCustomer;

@RestController
@RequestMapping("/mysql")
public class MySqlController {
    private int pageSize = 10;

    @Autowired
    private CustomerRepository customerRepository;

    @Autowired
    private SimpleCustomerRepository simpleCustomerRepository;

    @RequestMapping("/customer")
    public Customer findCustomer(String id) {
        return customerRepository.getOne(id);
    }

    @RequestMapping("/update-customer")
    public OperationResult updateCustomer(String id) {
        OperationResult result = new OperationResult();
        Customer customer = customerRepository.getOne(id);

        if (customer == null) {
            result.setErrorMessage(String.format("Customer with id %d not found!", id));
            return result;
        }

        customer.setName("Test-Customer");
        Customer updatedCustomer = customerRepository.save(customer);
        result.setData(updatedCustomer);
        return result;
    }

    @RequestMapping("/paging-customers")
    public List<Customer> pagingCustomers(int page) {
        Pageable pageable = PageRequest.of(page, pageSize, Sort.by(Direction.DESC, "Created"));
        Page<Customer> customerPage = customerRepository.findAll(pageable);
        System.out.println(String.format("TotalElements: %d", customerPage.getTotalElements()));
        System.out.println(String.format("TotalPages: %d", customerPage.getTotalPages()));
        return customerPage.getContent();
    }

    @RequestMapping("/paging-simple-customers")
    public List<SimpleCustomer> pagingSimpleCustomers(int page) throws ParseException {
        Date startDate = DateFormatUtils.parse("2018-01-01", "yyyy-MM-dd");
        return simpleCustomerRepository.paging(startDate, (page - 1) * pageSize, pageSize);
    }
}

除此之外，save方法也用于新增，delete方法用于删除，不再赘述。

Demo代码