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2018/6/13

JPA + Hibernate + MySQL persistence.xml 基本設定

JPA 2.1 + Hibernate 5.2.17 + MySQL 8.0.11 persistence.xml的一些設定。

首先用Maven下載需要的jar。

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>idv.matt</groupId>
  <artifactId>mytest</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>mytest</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>3.8.1</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>8.0.11</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-core -->
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-core</artifactId>
        <version>5.2.17.Final</version>
    </dependency>
    <!-- https://mvnrepository.com/artifact/org.hibernate/hibernate-entitymanager -->
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-entitymanager</artifactId>
        <version>5.2.17.Final</version>
    </dependency>
  </dependencies>
</project>

如果你是以WAR來部屬應用程式，則JPA Hibernate的persistence.xml的位置必須放在WAR檔中的WEB-INF/classes/META-INF/目錄下，所以就是在(例如Eclipse)專案類別路徑(classpath)下的META-INF目錄(src/META-INF/。是folder，不是package)(參考)。

JPA Hibernate的persistence.xml的範例如下

persistence.xml

<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
                                 http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd" 
             version="2.1">

    <persistence-unit name="mydb" transaction-type="RESOURCE_LOCAL">
        <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
        <class>idv.matt.entity.Employee</class>
        <properties>
            <property name="javax.persistence.jdbc.driver" value="com.mysql.cj.jdbc.Driver" />
            <property name="javax.persistence.jdbc.url" value="jdbc:mysql://localhost:3306/mydb?useSSL=false&characterEncoding=utf-8" />
            <property name="javax.persistence.jdbc.user" value="matt" />
            <property name="javax.persistence.jdbc.password" value="12345" />
            <property name="hibernate.dialect" value="org.hibernate.dialect.MySQLDialect" />
            <property name="hibernate.show_sql" value="true" />
            <property name="hibernate.hbm2ddl.auto" value="none" />
        </properties>
    </persistence-unit>

</persistence>

關於persistence.xml中Hibernate的設定參數可參考這裡。

Entity類別Employee，其對映資料庫的employee資料表。資料庫中email欄位有唯一限制(unique)。

Employee.java

package idv.matt.entity;

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

@Entity
@Table(name="employee")
public class Employee {
  
  @Id
  @Column(name="id")
  private Integer id;
  
  @Column(name="name")
  private String name;
  
  @Column(name="email", unique=true)
  private String email;
  
  public Integer getId() {
    return id;
  }
  public void setId(Integer id) {
    this.id = id;
  }
  public String getName() {
    return name;
  }
  public void setName(String name) {
    this.name = name;
  }
  public String getEmail() {
    return email;
  }
  public void setEmail(String email) {
    this.email = email;
  }

}

測試查詢資料的程式碼如下，直接使用main方法來測試。在Hibernate JPA要取得EntityManager來下SQL。

Main.java

package idv.matt.main;

import java.util.List;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;

import idv.matt.entity.Employee;

public class Main {

  public static void main(String[] args) {
    
    EntityManagerFactory emf = Persistence.createEntityManagerFactory("mydb");
    EntityManager em = emf.createEntityManager();
    Query query = em.createNativeQuery("select * from employee", Employee.class);
    
    @SuppressWarnings("unchecked")
    List<Employee> employeeList = query.getResultList();
    
    em.close();
    
    for(Employee employee : employeeList) {
      System.out.println(employee.getEmail());
    }
  }
}

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