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
1 server.port=90062 spring.application.name=spring-data-jpa3 4 #Serialize JPA entity to Json string.5 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
1 #Data source 1 2 db1.sqlserver.driver-class-name=com.microsoft.sqlserver.jdbc.SQLServerDriver 3 db1.sqlserver.url=${DB1_URL:jdbc:sqlserver://127.0.0.1:1433;DatabaseName=MyTestDb1} 4 db1.sqlserver.username=${DB1_UID:tester} 5 db1.sqlserver.password=${DB1_PWD:tester}
6 db1.sqlserver.initial-size=1 7 db1.sqlserver.min-idle=1 8 db1.sqlserver.max-active=20 9 db1.sqlserver.max-wait=6000010 db1.sqlserver.time-between-eviction-runs-millis=6000011 db1.sqlserver.min-evictable-idle-time-millis=30000012 db1.sqlserver.validation-query=select 113 db1.sqlserver.test-on-borrow=true14 db1.sqlserver.test-While-Idle=true15 db1.sqlserver.test-on-return=false16 db1.sqlserver.pool-prepared-statements=false17 db1.sqlserver.max-pool-prepared-statement-per-connection-size= 19 db1.sqlserver.filter.stat.enabled=true20 db1.sqlserver.filter.stat.db-type=mssql21 db1.sqlserver.filter.stat.log-slow-sql=true22 db1.sqlserver.filter.stat.slow-sql-millis=200023 24 db1.sqlserver.jpa.hibernate.dialect=org.hibernate.dialect.SQLServerDialect25 db1.sqlserver.jpa.hibernate.show_sql=true26 db1.sqlserver.jpa.hibernate.format_sql=true27 28 #Data source 229 db2.mysql.driver-class-name=com.mysql.jdbc.Driver30 db2.mysql.url=${DB2_URL:jdbc:mysql://127.0.0.1:3306/Test}?useUnicode=true&useSSL=false31 db2.mysql.username=${DB2_UID:tester}32 db2.mysql.password=${DB2_PWD:tester}33 db2.mysql.initial-size=134 db2.mysql.min-idle=135 db2.mysql.max-active=2036 db2.mysql.max-wait=6000037 db2.mysql.time-between-eviction-runs-millis=6000038 db2.mysql.min-evictable-idle-time-millis=30000039 db2.mysql.validation-query=select 140 db2.mysql.test-on-borrow=true41 db2.mysql.test-While-Idle=true42 db2.mysql.test-on-return=false43 db2.mysql.pool-prepared-statements=false44 db2.mysql.max-pool-prepared-statement-per-connection-size=2045 46 db2.mysql.filter.stat.enabled=true47 db2.mysql.filter.stat.db-type=mysql48 db2.mysql.filter.stat.log-slow-sql=true49 db2.mysql.filter.stat.slow-sql-millis=200050 51 db2.mysql.jpa.hibernate.dialect=org.hibernate.dialect.MySQLDialect52 db2.mysql.jpa.hibernate.show_sql=true53 db2.mysql.jpa.hibernate.format_sql=true54 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/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：
1 import java.util.Properties; 2 3 import javax.sql.DataSource; 4 5 import org.springframework.boot.context.properties.ConfigurationProperties; 6 import org.springframework.context.annotation.Bean; 7 import org.springframework.context.annotation.Configuration; 8 import org.springframework.context.annotation.Primary; 9 import org.springframework.context.annotation.PropertySource;10 import org.springframework.data.jpa.repository.config.EnableJpaRepositories;11 import org.springframework.orm.jpa.JpaTransactionManager;12 import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;13 import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;14 import org.springframework.transaction.PlatformTransactionManager;15 16 import com.alibaba.druid.spring.boot.autoconfigure.DruidDataSourceBuilder;17 18 import devutility.internal.util.PropertiesUtils;19 20 @Configuration21 @PropertySource("classpath:db.properties")22 @EnableJpaRepositories(basePackages = "devutility.test.database.springdatajpa.dao.mssql", entityManagerFactoryRef = "entityManagerFactory1", transactionManagerRef = "transactionManager1")23 public class DataSource1Configuration {24@Primary25@Bean26@ConfigurationProperties("db1.sqlserver")27public DataSource dataSource1() {28 return DruidDataSourceBuilder.create().build();29}30 31@Bean32@ConfigurationProperties("db1.sqlserver.jpa")33public Properties jpaProperties1() {34 return new Properties();35}36 37@Primary38@Bean39public LocalContainerEntityManagerFactoryBean entityManagerFactory1() {40 LocalContainerEntityManagerFactoryBean localContainerEntityManagerFactoryBean = new LocalContainerEntityManagerFactoryBean();41 localContainerEntityManagerFactoryBean.setDataSource(dataSource1());42 localContainerEntityManagerFactoryBean.setPackagesToScan(new String[] { "devutility.test.database.springdatajpa.dao.mssql.entity" });43 localContainerEntityManagerFactoryBean.setJpaVendorAdapter(new HibernateJpaVendorAdapter());44 localContainerEntityManagerFactoryBean.setJpaPropertyMap(PropertiesUtils.toMap(jpaProperties1()));45 return localContainerEntityManagerFactoryBean;46}47 48@Bean49public PlatformTransactionManager transactionManager1() {50 JpaTransactionManager transactionManager = new JpaTransactionManager();51 transactionManager.setEntityManagerFactory(entityManagerFactory1().getObject());52 return transactionManager;53}54 }
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;@Configurationpublic class DruidConfiguration {@Beanpublic 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;}@Beanpublic 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 druidspring.datasource.druid.stat-view-servlet.enabled=truespring.datasource.druid.stat-view-servlet.url-pattern=/druid/*spring.datasource.druid.stat-view-servlet.login-username=adminspring.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 {@Idprivate 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 {@Idprivate 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;@Autowiredprivate CustomerRepository customerRepository;@Autowiredprivate 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("-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
