初衷

项目中有用到spring data jpa，简单看了一下，在基础的数据库操作上，要比mybatis好用，简化了持久层的操作，使coder可以专注于业务逻辑的实现。网上参考了一些文章，实际coding的时候还是出好多错误。这里通过CRUD，记录摸索填坑的过程。详细的概念可以参考文末的文章。

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创建工程

创建一个maven工程。

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配置

web.xml

     
       
      
       spring-jpa-web
        
        
          
       
        appServlet
           
       
        org.springframework.web.servlet.DispatcherServlet
           
             
        
         contextConfigLocation
              
        
         classpath:spring.xml
            
           
       
        1
         
        
          
       
        appServlet
           
       
        /
         
      
     

pom.xml

特别说明，spring-data-jpa要用版本1.9.0.RELEASE。

     
         
      
       4.0.0
          
      
       org.wxs.spring
          
      
       spring-jpa-web
          
      
       war
          
      
       0.1.0
          
              
       
        4.3.0.RELEASE
               
       
        1.9.0.RELEASE
               
       
        1.12.6.RELEASE
               
       
        4.2.5.Final
           
          
              
               
               
                   
        
         org.springframework.data
                    
        
         spring-data-jpa
                    
        
         ${spring_jpa_version}
                
               
               
                   
        
         org.hibernate
                    
        
         hibernate-core
                    
        
         ${hibernate.version}
                
               
                   
        
         org.hibernate
                    
        
         hibernate-entitymanager
                    
        
         ${hibernate.version}
                
               
                   
        
         org.hibernate
                    
        
         hibernate-ehcache
                    
        
         ${hibernate.version}
                
               
               
                   
        
         org.apache.tomcat
                    
        
         tomcat-jdbc
                    
        
         7.0.54
                
               
               
                   
        
         mysql
                    
        
         mysql-connector-java
                    
        
         5.1.35
                
               
               
                   
        
         org.springframework
                    
        
         spring-core
                    
        
         ${spring_version}
                
               
                   
        
         org.springframework
                    
        
         spring-beans
                    
        
         ${spring_version}
                
               
                   
        
         org.springframework
                    
        
         spring-web
                    
        
         ${spring_version}
                
               
                   
        
         org.springframework
                    
        
         spring-webmvc
                    
        
         ${spring_version}
                
               
                   
        
         org.springframework
                    
        
         spring-context
                    
        
         ${spring_version}
                
               
                   
        
         org.springframework
                    
        
         spring-orm
                    
        
         ${spring_version}
                
               
                   
        
         org.springframework
                    
        
         spring-tx
                    
        
         ${spring_version}
                
               
                   
        
         org.springframework
                    
        
         spring-jdbc
                    
        
         ${spring_version}
                
               
                   
        
         org.springframework
                    
        
         spring-context-support
                    
        
         ${spring_version}
                
               
                   
        
         org.springframework
                    
        
         spring-test
                    
        
         ${spring_version}
                
               
               
               
                   
                    
        
         junit
                    
        
         junit
                    
                    
                    
                    
                    
        
         4.12
                    
        
         test
                
               
               
                   
        
         org.apache.tomcat
                    
        
         tomcat-servlet-api
                    
        
         8.0.3
                    
        
         provided
                
               
                   
        
         org.apache.tomcat
                    
        
         jsp-api
                    
        
         6.0.39
                    
        
         provided
                
               
                   
        
         jstl
                    
        
         jstl
                    
        
         1.2
                
               
                   
        
         javax.servlet.jsp
                    
        
         jsp-api
                    
        
         2.1
                    
        
         provided
                
               
           
      
     

spring.xml

     
         
      
       Spring公共配置
          
          
          
          
              
               
               
               
                   
                        
                         
         
          org.hibernate.cfg.ImprovedNamingStrategy
                     
                
               
                   
                
           
          
              
               
               
           
          
          
          
          
              
           
          
          
          
              
           
          
          
              
               
               
               
               
               
               
               
               
               
           
          
          
      
     

属性文件

jdbc.properties

jdbc.driver=com.mysql.jdbc.Driverjdbc.url=jdbc:mysql://localhost:3306/seckill?useUnicode=true&characterEncoding=utf8jdbc.username=rootjdbc.password=adminjdbc.pool.maxIdle=5jdbc.pool.maxActive=10

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Entity

新建表

新建表 user

实体类

新建实体类User

@Entity@Table(name = "user")public class User {
        @Id    @GeneratedValue(strategy = GenerationType.IDENTITY)    private Integer  id;    @Column(name = "name")    private String name;    @Column(name = "password")    private String password;    @Column(name = "birthday")    private Date birthday;    /** * The default constructor only exists for the sake of JPA. You won’t use it directly, so it is designated as protected. */    protected User() {    }    public User(String name, String password, Date birthday) {        this.name = name;        this.password = password;        this.birthday = birthday;    }getter、setter省略

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DAO层

创建接口UserRepository

public interface UserRepository extends JpaRepository
     
       {
    }
     

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测试

新增

@Test    public void test1(){        User user=new User("SL1","123",new Date());        userRepository.save(user);        System.out.println("save success");    }

查询

查询全部

@Test    public void test2(){        for (User user:userRepository.findAll()) {            System.out.println(user);        }        System.out.println("search all success");    }

查询结果

User{id=9, name='SL1', password='123', birthday=2017-01-12 00:00:00.0}User{id=10, name='SL1', password='123', birthday=2017-01-12 00:00:00.0}User{id=11, name='SL1', password='123', birthday=2017-01-13 00:00:00.0}search all success

根据ID查询

@Test    public void test3(){        System.out.println(userRepository.findOne(9));        System.out.println("search one success");    }

查询结果

User{id=9, name='SL1', password='123', birthday=2017-01-12 00:00:00.0}search one success

更新

如果有Id，jpa会认为是更新，没有则是新增。

@Test    public void test4(){        User user=new User("SL99","123",new Date());        user.setId(9);        userRepository.save(user);        test3();        System.out.println("update success");    }

更新成功

User{id=9, name='SL99', password='123', birthday=2017-01-13 00:00:00.0}search one successupdate success

删除

@Test    public void test5(){        userRepository.delete(9);        test3();        System.out.println("delete success");    }

删除成功

nullsearch one successdelete success

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踩过的坑

坑1

java.lang.AbstractMethodError: org.springframework.data.repository.core.support.RepositoryFactorySupport.getTargetRepository(Lorg/springframework/data/repository/core/RepositoryInformation;)Ljava/lang/Object;

Deleting the spring-data-commons and changing the spring-data-jpa version to 1.9.0.RELEASE like @peeskillet said now works fine!

这也是为什么pom文件中spring-data-jpa要配置1.9.0.RELEASE的版本。

坑2

java.lang.IllegalArgumentException: Not an managed type: class java.lang.Object

Dao层的接口继承JpaRepository的时候加上泛型。添加域对象类型和主键类型。

public interface UserRepository extends JpaRepository<User,Integer>

坑3

org.hibernate.InstantiationException: No default constructor for entity: com.wx.jpa.entities.User

新增、根据ID查询这2个方法不会报这个异常。

Hibernate在创建Bean的时候需要User的默认构造方法。中也有讲到。

You also have two constructors. The default constructor only exists

for the sake of JPA. You won’t use it directly, so it is designated

as protected. The other constructor is the one you’ll use to create

instances of Customer to be saved to the database.

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欢迎感兴趣的同学指正。。。

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参考：