Spring data JPA allows us not to write any boilerplate code by adding an additional repository layer.<\/p>\n
1.2 History of JPA<\/h3>\n
JPA2.0: –\u00a0<\/strong>The development of JPA2.0 started in 2007 as JSR 317. The version was marked as 2.0 as it could not gain the common consensus for 1.0. The focus was to address the features available as part of famous vendor ORMs.<\/p>\n JPA 2.1:-\u00a0<\/strong>JPA2.1 started in July 2011 as JSR 338. Some of the main features were Entity graph, stored procedures, converters, etc.<\/p>\n JPA 2.2:-<\/strong>\u00a0JPA2.2 is the latest addition to JPA series in 2017. It includes support for Java 8 date and time type, ability to stream a query result.<\/p>\n JPA is still undergoing lot of changes and we can epect a newer version of JPA soon.<\/p>\n Spring Data Commons project provides repository abstraction which is extended by the datastore-specific subprojects.<\/p>\n We have to be familiar with the Spring Data repository interfaces as it will help us with the implementation of the interfaces. Let’s have a look at the interfaces.<\/p>\n Spring Data Commons: –<\/strong>\u00a0Following interfaces are provided as part of this project:<\/p>\n Spring Data JPA: –<\/strong>\u00a0 This project provides the following interfaces:<\/p>\n The repository hierarchy looks as follows:<\/p>\n Let’s try to understand Spring Data JPA through a sample program.<\/p>\n Let us consider a use case where we have to fetch data from a database based on a query. Writing a custom query is a very useful case. Spring Data JPA has different ways of writing custom queries. We will broadly classify the ways as mentioned below.<\/p>\n Automatic Custom Queries:<\/strong> The automatic custom query creation is also known as query creation from the method name.\u00a0Spring Data JPA has a built-in mechanism for query creation which can be used for parsing queries straight from the method name of a query method. The mechanism first removes common prefixes from the method name and parses the constraints of the query from the rest of the method name. In order to use this approach, we have to make sure\u00a0the method names of your repository interface are created by combining the property names of an entity object and the supported keywords.<\/p>\n The advantage of using this approach is that it makes it very easy to implement. But the limitation is if the query contains more than one parameter than the method name will be not readable. Also the keywords that are not supported by JPA like lower will not be useful with this approach.<\/p>\n Manual Custom Queries:<\/strong> Manual Custom queries are also known as queries creation using The advantage of this approach is you can use JPA query language for the creation of a query. Also, the query stays in repository layer. Limitation of this approach is The program mentioned below uses both the approaches.<\/p>\n The point to consider is\u00a0because the default Spring ORM templates are not used with SPring JPA, are we losing exception translation by using Spring Data JPA?nAre we not going to get our JPA exceptions translated to Spring\u2019s DataAccessException hierarchy?<\/p>\n The answer is No<\/strong>. Exception translation is still enabled by the use of the annotation Let us look at the technologies and tool used for building the program.<\/p>\n Our project structure will look as shown in the image below.<\/p>\n <\/p>\n The above project structure is using Maven. This project can also be created using Gradle and the pom.xml will get replaced with build.gradle file. The structure of the project will defer slightly with the usage of Gradle for the build.<\/p>\n As part of the program, we will try to create a simple web service using spring boot. This web service will be used for data manipulation on PostgreSQL database.<\/p>\n The pom.xml for SpringData JPA with Spring Boot<\/em><\/span><\/p>\n The pom.xml file will contain the dependencies that will be needed as part of the program.<\/p>\n The Application.java class for us is\u00a0 SpringJpaPostgreSqlApplication.java class for Spring Boot<\/em><\/span><\/p>\n The We are going to create an Model class for the program<\/em><\/span><\/p>\n The repository interface is used for extending the CRUD interface. This interface adds the layer of a repository in the program. Spring Data JPA provides two major ways of creating queries. These queries are then used in the repository interface to fetch the data from the database.<\/p>\n Repository class for extending CRUD repository<\/em><\/span><\/p>\n The Automatic Custom Query:<\/strong><\/p>\n The method Manual Custom Query:<\/strong><\/p>\n In this method we have manually defined a query to fetch the data based on age and the query is then bound with the As part of spring boot for connecting to the database, we will provide the details in the properties file. The properties file will look as shown below.<\/p>\n application.properties file for the spring boot<\/em><\/span><\/p>\n As part of the properties file, the database URL and credentials are provided. The property The controller is the most important class of the complete program. This is the class responsible for all the url mapping. We have added the repository methods for data manipulation in this class itself.<\/p>\n Controller class for the program<\/em><\/span><\/p>\n In this class, we have autowired the repository and are using the methods available in the interface for data retrieval, insertion and deletion.<\/p>\n For running the spring boot application we have to provide the command Below mentioned queries can be used for the creation of Employee table in PostgreSQL.<\/p>\n SQL query for Employee table creation<\/em><\/span><\/p>\n Lets us check the data available in the database. The current data available in the database is shown below.<\/p>\n Now let’s try the findall\u00a0API using postman collection to get the rows as result. The result will look as shown below on postman.<\/p>\n In order to add some employee object in a database. We will use the save API and will pass an employee object.<\/p>\n Let’s check the database post the save API usage. The database will look as shown below.<\/p>\n Similarly, we can use the 1.3 Spring Data Repositories<\/h3>\n
\n
Repository<T, ID extends Serializable><\/em><\/a><\/code>\u00a0 :\u00a0This interface is a marker interface.\n\n
CrudRepository<T, ID extends Serializable><\/em><\/a><\/code>\u00a0:\u00a0It provides CRUD operations for the managed entity.<\/li>\nPagingAndSortingRepository<T, ID extends Serializable><\/em><\/a><\/code>\u00a0:\u00a0This interface declares the methods that are used to sort and paginate entities that are retrieved from the database.<\/li>\nQueryDslPredicateExecutor<T><\/em><\/a><\/code>\u00a0: It is not a \u201crepository interface\u201d. It declares the methods that are used to retrieve entities from the database by using\u00a0QueryDsl<\/a><\/code>\u00a0Predicate<\/em>\u00a0objects.<\/li>\n<\/ul>\n\n
JpaRepository<T, ID extends Serializable><\/em><\/a><\/code>\u00a0 :\u00a0This interface is a JPA specific repository interface that combines the methods declared by the common repository interfaces behind a single interface.<\/li>\nJpaSpecificationExecutor<T><\/em><\/a><\/code>\u00a0: This is again not a \u201crepository interface\u201d. It declares the methods that are used to retrieve entities from the database by using\u00a0Specification<T><\/em><\/a><\/code>\u00a0objects that use the JPA criteria API.<\/li>\n<\/ul>\n![\"\"](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2018\/04\/springdatajrepositories_jcg.jpg\")
<\/a>1.4 Spring Data Custom Query<\/h3>\n
@Query<\/code> tag.\u00a0The @Query<\/code> annotation will be used to create queries using the JPA query language and for binding these queries directly to the methods of your repository interface. When the query method is called, Spring Data JPA will execute the query specified by the @Query<\/code> annotation.<\/p>\n@Query<\/code> can be only used when JPA query language is supported.1.5 Spring Data JPA Exception Translation<\/h3>\n
@Repository<\/code> on the DAO. The annotation enables a Spring bean postprocessor to advice\u00a0all @Repository<\/code> beans with all the PersistenceExceptionTranslator<\/code> instances found in the Container and provides exception translation just as before.<\/p>\n2. Tools and Technologies<\/h2>\n
\n
3. Project Structure<\/h2>\n
![\"\"](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2018\/04\/ProjectStructure_JCG-1.jpg\")
<\/a>4. An objective of the Program<\/h2>\n
4.1 pom.xml<\/h3>\n
pom.xml<\/code> file for the program will look as mentioned below.<\/p>\n<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<project xmlns=\"http:\/\/maven.apache.org\/POM\/4.0.0\" xmlns:xsi=\"http:\/\/www.w3.org\/2001\/XMLSchema-instance\"\n\txsi:schemaLocation=\"http:\/\/maven.apache.org\/POM\/4.0.0 http:\/\/maven.apache.org\/xsd\/maven-4.0.0.xsd\">\n\t<modelVersion>4.0.0<\/modelVersion>\n\n\t<groupId>com.springjpa<\/groupId>\n\t<artifactId>SpringJPA-PostgreSQL<\/artifactId>\n\t<version>0.0.1<\/version>\n\t<packaging>jar<\/packaging>\n\n\t<name>SpringJPA-PostgreSQL<\/name>\n\t<description>Demo project for Spring Boot JPA - PostgreSQL<\/description>\n\n\t<parent>\n\t\t<groupId>org.springframework.boot<\/groupId>\n\t\t<artifactId>spring-boot-starter-parent<\/artifactId>\n\t\t<version>2.0.1.RELEASE<\/version>\n\t\t<relativePath\/> \n\t<\/parent>\n\n\t<properties>\n\t\t<project.build.sourceEncoding>UTF-8<\/project.build.sourceEncoding>\n\t\t<project.reporting.outputEncoding>UTF-8<\/project.reporting.outputEncoding>\n\t\t<java.version>1.9<\/java.version>\n\t<\/properties>\n\n\t<dependencies>\n\t\t<dependency>\n\t\t\t<groupId>org.springframework.boot<\/groupId>\n\t\t\t<artifactId>spring-boot-starter-data-jpa<\/artifactId>\n\t\t<\/dependency>\n\t\t<dependency>\n\t\t\t<groupId>org.springframework.boot<\/groupId>\n\t\t\t<artifactId>spring-boot-starter-web<\/artifactId>\n\t\t<\/dependency>\n\n\t\t<dependency>\n\t\t\t<groupId>org.postgresql<\/groupId>\n\t\t\t<artifactId>postgresql<\/artifactId>\n\t\t\t<scope>runtime<\/scope>\n\t\t<\/dependency>\n\t\t<dependency>\n\t\t\t<groupId>org.springframework.boot<\/groupId>\n\t\t\t<artifactId>spring-boot-starter-test<\/artifactId>\n\t\t\t<scope>test<\/scope>\n\t\t<\/dependency>\n\t\t<dependency>\n <groupId>javax.xml.bind<\/groupId>\n <artifactId>jaxb-api<\/artifactId>\n <version>2.3.0<\/version>\n<\/dependency>\n\t<\/dependencies>\n\n\t<build>\n\t\t<plugins>\n\t\t\t<plugin>\n\t\t\t\t<groupId>org.springframework.boot<\/groupId>\n\t\t\t\t<artifactId>spring-boot-maven-plugin<\/artifactId>\n\t\t\t<\/plugin>\n\t\t<\/plugins>\n\t<\/build>\n\t\n\n\n<\/project>\n<\/pre>\n
4.2 Application class<\/h3>\n
SpringJpaPostgreSqlApplication.java<\/code> class. The class looks as shown below.<\/p>\npackage com.tutorial;\n\nimport org.springframework.beans.factory.annotation.Autowired;\nimport org.springframework.boot.CommandLineRunner;\nimport org.springframework.boot.SpringApplication;\nimport org.springframework.boot.autoconfigure.SpringBootApplication;\n\nimport com.tutorial.repo.EmployeeRepository;\n\n@SpringBootApplication\npublic class SpringJpaPostgreSqlApplication implements CommandLineRunner{\n\n\t@Autowired\n\tEmployeeRepository repository;\n\t\n\tpublic static void main(String[] args){\n\t\tSpringApplication.run(SpringJpaPostgreSqlApplication.class, args);\n\t}\n\n\tpublic void run(String... args) throws Exception {\n\t\t\/\/ TODO Auto-generated method stub\n\t\t\n\t}\n\n}\n<\/pre>\nCommandLineRunner<\/code> interface is used for to indicate that a bean should run when it is contained within a Spring Application.<\/p>\n4.3 Model Class<\/h3>\n
Employee.java<\/code> class as the model class. The class will look as shown below.<\/p>\npackage com.tutorial.model;\n\nimport java.io.Serializable;\n\nimport javax.persistence.Column;\nimport javax.persistence.Entity;\nimport javax.persistence.GeneratedValue;\nimport javax.persistence.GenerationType;\nimport javax.persistence.Id;\nimport javax.persistence.Table;\n\n@Entity\n@Table(name = \"employee\")\npublic class Employee implements Serializable {\n\n\tprivate static final long serialVersionUID = -3009157732242241606L;\n\t@Id\n\t@GeneratedValue(strategy = GenerationType.AUTO)\n\t@Column(name=\"id\")\n\tprivate long id;\n\n\t@Column(name = \"firstname\")\n\tprivate String firstName;\n\n\t@Column(name = \"lastname\")\n\tprivate String lastName;\n\t\n\t@Column(name = \"age\")\n\tprivate int age;\n\n\tprotected Employee() {\n\t}\n\n\tpublic Employee(String firstName, String lastName,int age) {\n\t\tthis.firstName = firstName;\n\t\tthis.lastName = lastName;\n\t\tthis.age = age;\n\t}\n\n\t@Override\n\tpublic String toString() {\n\t\treturn String.format(\"Employee[id=%d, firstName='%s', lastName='%s', age='%d']\", id, firstName, lastName,age);\n\t}\n\n\t\n\tpublic long getId() {\n\t\treturn id;\n\t}\n\n\tpublic void setId(long id) {\n\t\tthis.id = id;\n\t}\n\n\tpublic String getFirstName() {\n\t\treturn firstName;\n\t}\n\n\tpublic void setFirstName(String firstName) {\n\t\tthis.firstName = firstName;\n\t}\n\n\tpublic String getLastName() {\n\t\treturn lastName;\n\t}\n\n\tpublic void setLast_Name(String lastName) {\n\t\tthis.lastName = lastName;\n\t}\n\n\tpublic int getAge() {\n\t\treturn age;\n\t}\n\n\tpublic void setAge(int age) {\n\t\tthis.age = age;\n\t}\n}\n<\/pre>\n@Entity<\/code>: Is used to define that the class is an Entity class.
\n@Table<\/code>: This annotation is used for specifying the table name which is defined in the database.
\n@Id<\/code>: Id annotation is used for specifying the Id attribute
\n@GeneratedValue<\/code>: This is used when we want to set automatically generated value. GenerationType<\/code> is the mechanism that is used for generating the value for the specific column.
\n@Column<\/code>: This annotation is used for mapping the columns from the table with the attributes in the class.
\n[ulp id=’c4qGwqz2zZ7CesZd’]
\n <\/p>\n4.4 Repository Interface<\/h3>\n
package com.tutorial.repo;\n\nimport java.util.List;\n\nimport org.springframework.data.jpa.repository.Query;\nimport org.springframework.data.repository.CrudRepository;\nimport org.springframework.data.repository.query.Param;\nimport org.springframework.stereotype.Repository;\n\nimport com.tutorial.model.Employee;\n\n@Repository\npublic interface EmployeeRepository extends CrudRepository<Employee, Long>{\n\tList findByLastName(String lastName);\n\t\n@Query(\"SELECT e FROM Employee e WHERE e.age = :age\")\n public List findByAge(@Param(\"age\") int age);\n}\n\n<\/pre>\nCrudRepository<\/code> is the interface from SpringData Common project. The two methods mentioned above for query creation is used at the below-mentioned places in the code.<\/p>\n List findByLastName(String lastName);<\/pre>\n
findByLastName<\/code> contains the last name as the parameter which will be used for the search of data. Also, the query will be automatically created using JPA query builder.<\/p>\n @Query(\"SELECT e FROM Employee e WHERE e.age = :age\")\n public List findByAge(@Param(\"age\") int age);<\/pre>\n
findByAge<\/code> method.<\/p>\n4.5 Properties file<\/h3>\n
spring.datasource.url=jdbc:postgresql:\/\/localhost:5432\/postgres\nspring.datasource.username=postgres\nspring.datasource.password=password\nspring.jpa.generate-ddl=true\nspring.jpa.show-sql=true\nspring.jpa.properties.hibernate.format_sql=true\n<\/pre>\n
spring.jpa.show-sql=true<\/code> shows the SQL query generated during the data manipulation by JPA.<\/p>\n4.6 Controller class<\/h3>\n
package com.tutorial.controller;\n\nimport java.util.List;\nimport java.util.Optional;\n\nimport org.springframework.beans.factory.annotation.Autowired;\nimport org.springframework.http.HttpStatus;\nimport org.springframework.web.bind.annotation.RequestBody;\nimport org.springframework.web.bind.annotation.RequestMapping;\nimport org.springframework.web.bind.annotation.RequestMethod;\nimport org.springframework.web.bind.annotation.RequestParam;\nimport org.springframework.web.bind.annotation.RestController;\n\nimport com.tutorial.model.Employee;\nimport com.tutorial.repo.EmployeeRepository;\n\n@RestController\n@RequestMapping(\"\/employee\")\npublic class WebController {\n\t@Autowired\n\tEmployeeRepository repository;\n\t\n\t@RequestMapping(value=\"\/save\",method = RequestMethod.POST)\n\tpublic HttpStatus insertEmployee(@RequestBody Employee employee){\n\t\tboolean status = repository.save(employee) != null;\t\t\n\t\treturn status? HttpStatus.CREATED : HttpStatus.BAD_REQUEST;\n\t}\n\t\n\t\n\t@RequestMapping(\"\/findall\")\n\tpublic List findAll(){\n\t\t\n\t\t\n\t\treturn (List) repository.findAll();\n\t}\n\t\n\t@RequestMapping(\"\/findbyid\")\n\tpublic Optional findById(@RequestParam(\"id\") long id){\n\t\tOptional result = repository.findById(id);\n\t\treturn result;\n\t}\n\t\n\t@RequestMapping(\"\/findbylastname\")\n\tpublic List fetchDataByLastName(@RequestParam(\"lastname\") String lastName){\n\t\t \t\t\n\t\treturn repository.findByLastName(lastName);\n\t}\n\t@RequestMapping(\"\/findbyage\")\n\tpublic List fetchDataByAge(@RequestParam(\"age\") int age){\n\t\t \t\t\n\t\treturn repository.findByAge(age);\n\t}\n}\n<\/pre>\n@RestController<\/code> tag is used for defining the class as a rest controller class.
\n@RequestMapping<\/code> tag specifies the path mapping for the request. Value attribute specifies the URL mapping and the method attributes specifies the type of method it is like GET, POST, PUT, etc.
\nIf we don’t specify the method attribute by default the method is considered as GET method.<\/p>\nspring-boot: run<\/code> .<\/p>\n5. Output<\/h2>\n
create table employee (\nid serial not null primary key,\nfirstName varchar(20) not null,\nlastName varchar(20) not null,\nage integer not null\n);<\/pre>\n
![\"\"](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2018\/04\/Result_JCG.jpg\")
<\/a>![\"\"](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2018\/04\/Findall_JCG.jpg\")
<\/a>![\"\"](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2018\/04\/Save_JCG-1.jpg\")
<\/a>![\"\"](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2018\/04\/AfterSave_JCG.jpg\")
<\/a>findbylastname<\/code> API for finding the records having the last name provided in the request parameter.<\/p>\n
![\"\"](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2018\/04\/findbylastname_JCG.jpg\")
<\/a>![\"\"](\"http:\/\/www.javacodegeeks.com\/wp-content\/uploads\/2018\/05\/findbyage_JCG.jpg\")
<\/a>