Spring Boot – H2 数据库

H2 是一个嵌入式、开源和内存数据库。它是一个用Java编写的关系数据库管理系统。它是一个客户端/服务器应用程序。它将数据存储在内存中，而不是将数据持久存储在磁盘上。在这里，我们将讨论如何使用 H2 数据库在 Spring Boot 中配置和执行一些基本操作。

H2 数据库的一些主要功能是：

• 非常快速的开源 JDBC API
• 嵌入式和服务器模式；基于磁盘或内存中的数据库
• 事务支持，多版本并发
• 基于浏览器的控制台应用程序
• 加密数据库
• 全文搜索
• 占用空间小的纯Java ：大约 2.5 MB 的 jar 文件大小
• ODBC 驱动程序

在 Spring Boot 应用程序中配置 H2 数据库

第一步：添加依赖

要在 Spring Boot 应用程序中使用 H2 数据库，我们必须在pom.xml文件中添加以下依赖项：

dependency>
      com.h2database
      h2
      runtime
 

第 2 步：在 application.properties 文件中写入一些属性

# H2 Database
spring.h2.console.enabled=true
spring.datasource.url=jdbc:h2:mem:dcbapp
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect

让我们通过打开 H2 数据库控制台来了解这些属性是什么。

H2 控制台：默认情况下，H2 数据库的控制台视图是禁用的。在访问 H2 数据库之前，我们必须使用以下属性启用它。

spring.h2.console.enabled=true

一旦我们启用了 H2 控制台，现在我们可以通过调用 URL http://localhost:8082/h2-console在浏览器中访问 H2 控制台。

Note: Provide your port number in which your spring application is running

下图为H2数据库的控制台视图。

例子：

我们将通过创建 Spring Boot 应用程序并使用 H2 数据库来执行一些基本的 CRUD 操作。

第一步：参考这篇文章如何使用 IntelliJ IDEA 创建 Spring Boot 项目并创建一个 Spring Boot 项目。

第二步：添加以下依赖

• 春季网络
• H2 数据库
• 龙目岛
• 春季数据 JPA

下面是pom.xml文件的完整代码。请检查您是否遗漏了什么。

XML

 

    4.0.0
    
        org.springframework.boot
        spring-boot-starter-parent
        2.5.5
         
    
    com.amiya
    Spring-Boot-Demo-Project
    1.0.0-SNAPSHOT
    Spring-Boot-Demo-Project
    Demo project for Spring Boot
    
        11
    
    
        
            org.springframework.boot
            spring-boot-starter-web
        
 
        
            com.h2database
            h2
            runtime
        
 
        
            org.springframework.boot
            spring-boot-devtools
            runtime
            true
        
 
        
            org.springframework.boot
            spring-boot-starter-data-jpa
        
 
        
            org.springframework.boot
            spring-boot-starter-test
            test
        
 
        
            org.projectlombok
            lombok
            true
        
 
    
 
    
        
            
                org.springframework.boot
                spring-boot-maven-plugin
                
                    
                        
                            org.projectlombok
                            lombok
                        
                    
                
            
        
    
 

第 3 步：创建 4 个包，然后在这些包中创建一些类和接口，如下图所示

• 实体
• 存储库
• 服务
• 控制器

Note:

• Green Rounded Icon ‘I’ Buttons are Interface
• Blue Rounded Icon ‘C’ Buttons are Classes

第 4 步：在实体包内

在 Department 内部创建一个简单的 POJO 类。 Java文件。

例子：

Java

// Java Program to Demonstrate Department File
 
// Importing required package modules
package com.amiya.springbootdemoproject.entity;
 
// Importing required classes
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;
 
@Entity
@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
 
// Class
public class Department {
 
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long departmentId;
    private String departmentName;
    private String departmentAddress;
    private String departmentCode;
}

第 5 步：在存储库包中

创建一个简单的接口并将接口命名为 DepartmentRepository。正如我们上面讨论的那样，这个接口将扩展 CrudRepository。

示例下面是DepartmentRepository 的代码。Java

Java

package com.amiya.springbootdemoproject.repository;
 
import com.amiya.springbootdemoproject.entity.Department;
import org.springframework.data.repository.CrudRepository;
import org.springframework.stereotype.Repository;
 
// Annotation
@Repository
 
// Interface extending CrudRepository
public interface DepartmentRepository
    extends CrudRepository {
}

第 6 步：在服务包内

在包中创建一个名为DepartmentService的接口和一个名为DepartmentServiceImpl的类。

示例 1-A

Java

// Java Program to Demonstrate DepartmentService File
 
// Importing required package modules
package com.amiya.springbootdemoproject.service;
import com.amiya.springbootdemoproject.entity.Department;
// Importing required classes
import java.util.List;
 
// Interface
public interface DepartmentService {
 
    // Save operation
    Department saveDepartment(Department department);
 
    // Read operation
    List fetchDepartmentList();
 
    // Update operation
    Department updateDepartment(Department department,
                                Long departmentId);
 
    // Delete operation
    void deleteDepartmentById(Long departmentId);
}

示例 1-B

Java

// Java Program to Demonstrate DepartmentServiceImpl.java
// File
 
// Importing required package modules
package com.amiya.springbootdemoproject.service;
 
import com.amiya.springbootdemoproject.entity.Department;
import com.amiya.springbootdemoproject.repository.DepartmentRepository;
import java.util.List;
import java.util.Objects;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
 
// Annotation
@Service
 
// Class
public class DepartmentServiceImpl
    implements DepartmentService {
 
    @Autowired
    private DepartmentRepository departmentRepository;
 
    // Save operation
    @Override
    public Department saveDepartment(Department department)
    {
        return departmentRepository.save(department);
    }
 
    // Read operation
    @Override public List fetchDepartmentList()
    {
        return (List)
            departmentRepository.findAll();
    }
 
    // Update operation
    @Override
    public Department
    updateDepartment(Department department,
                     Long departmentId)
    {
        Department depDB
            = departmentRepository.findById(departmentId)
                  .get();
 
        if (Objects.nonNull(department.getDepartmentName())
            && !"".equalsIgnoreCase(
                department.getDepartmentName())) {
            depDB.setDepartmentName(
                department.getDepartmentName());
        }
 
        if (Objects.nonNull(
                department.getDepartmentAddress())
            && !"".equalsIgnoreCase(
                department.getDepartmentAddress())) {
            depDB.setDepartmentAddress(
                department.getDepartmentAddress());
        }
 
        if (Objects.nonNull(department.getDepartmentCode())
            && !"".equalsIgnoreCase(
                department.getDepartmentCode())) {
            depDB.setDepartmentCode(
                department.getDepartmentCode());
        }
 
        return departmentRepository.save(depDB);
    }
 
    // Delete operation
    @Override
    public void deleteDepartmentById(Long departmentId)
    {
        departmentRepository.deleteById(departmentId);
    }
}

第 7 步：在控制器包内

在包中创建一个名为DepartmentController的类。

例子

Java

// java Program to Illustrate DepartmentController File
 
// Importing required packages modules
package com.amiya.springbootdemoproject.controller;
 
import com.amiya.springbootdemoproject.entity.Department;
import com.amiya.springbootdemoproject.service.DepartmentService;
import java.util.List;
// Importing required classes
import javax.validation.Valid;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.*;
 
// Annotation
@RestController
 
// Class
public class DepartmentController {
 
    @Autowired private DepartmentService departmentService;
 
    // Save operation
    @PostMapping("/departments")
    public Department saveDepartment(
        @Valid @RequestBody Department department)
    {
        return departmentService.saveDepartment(department);
    }
 
    // Read operation
    @GetMapping("/departments")
    public List fetchDepartmentList()
    {
        return departmentService.fetchDepartmentList();
    }
 
    // Update operation
    @PutMapping("/departments/{id}")
    public Department
    updateDepartment(@RequestBody Department department,
                     @PathVariable("id") Long departmentId)
    {
        return departmentService.updateDepartment(
            department, departmentId);
    }
 
    // Delete operation
    @DeleteMapping("/departments/{id}")
    public String deleteDepartmentById(@PathVariable("id")
                                       Long departmentId)
    {
        departmentService.deleteDepartmentById(
            departmentId);
        return "Deleted Successfully";
    }
}

第 8 步：下面是 application.properties 文件的代码

server.port = 8082

# H2 Database
spring.h2.console.enabled=true
spring.datasource.url=jdbc:h2:mem:dcbapp
spring.datasource.driverClassName=org.h2.Driver
spring.datasource.username=sa
spring.datasource.password=password
spring.jpa.database-platform=org.hibernate.dialect.H2Dialect

现在运行您的应用程序，让我们在 Postman 中测试端点并参考我们的 H2 数据库。

在 Postman 中测试端点

端点 1： POST – http://localhost:8082/departments/

端点 2： GET - http://localhost:8082/departments/

端点 3： PUT - http://localhost:8082/departments/1

端点 4：删除 - http://localhost:8082/departments/1

最后，H2 数据库如下图所示： 如下：