开发基础知识 - Spring的应用结构

Content

以一个基于Dubbo，MyBatis的后台服务框架为例：

File structure:

api/
├── src/
│   ├── main/
│   │   ├── java/
│   │   │   └── com/
│   │   │       └── example/
│   │   │           └── api/
│   │   │               ├── entity/
│   │   │               │   └── User.java
│   │   │               ├── mapper/
│   │   │               │   └── UserMapper.java
│   │   │               ├── service/
│   │   │               │   ├── UserService.java
│   │   │               │   └── implementation/
│   │   │               │       └── UserServiceImpl.java
│   │   └── resources/
│   │       ├── applicationContext.xml
│   │       ├── dubbo-provider.xml
│   │       └── mapper/
│   │           └── UserMapper.xml
└── pom.xml

实体类

// User.java
package com.example.api.entity;

public class User {
    private Long id;
    private String name;
    private Integer age;

    // getters and setters
}

接口

// UserService.java
package com.example.api.service;

import com.example.api.entity.User;
import java.util.List;

public interface UserService {
    User getUserById(Long id);
    List<User> listUsers();
}

MyBatis接口

// UserMapper.java
package com.example.api.mapper;

import com.example.api.entity.User;
import java.util.List;

public interface UserMapper {
    User selectUserById(Long id);
    List<User> selectAllUsers();
}

MyBatis映射文件

<!-- UserMapper.xml -->
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
    PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
    "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.example.api.mapper.UserMapper">

    <select id="selectUserById" resultType="com.example.api.entity.User">
        SELECT id, name, age FROM user WHERE id = #{id}
    </select>

    <select id="selectAllUsers" resultType="com.example.api.entity.User">
        SELECT id, name, age FROM user
    </select>

</mapper>

服务实现类

// UserServiceImpl.java
package com.example.api.service.implementation;

import com.example.api.entity.User;
import com.example.api.mapper.UserMapper;
import com.example.api.service.UserService;
import java.util.List;

public class UserServiceImpl implements UserService {

    private UserMapper userMapper;

    // Spring 注入 setter
    public void setUserMapper(UserMapper userMapper) {
        this.userMapper = userMapper;
    }

    @Override
    public User getUserById(Long id) {
        return userMapper.selectUserById(id);
    }

    @Override
    public List<User> listUsers() {
        return userMapper.selectAllUsers();
    }
}

Dubbo配置文件

<!-- dubbo-provider.xml -->
<dubbo:application name="user-provider"/>
<dubbo:registry address="N/A"/> <!-- 如果没有注册中心 -->
<dubbo:protocol name="dubbo" port="20880"/>
<dubbo:service interface="com.example.api.service.UserService"
               ref="userService"/>

Spring配置文件

<!-- applicationContext.xml -->
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
       xsi:schemaLocation="
           http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
           http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
           http://dubbo.apache.org/schema/dubbo http://dubbo.apache.org/schema/dubbo/dubbo.xsd">

    <!-- 加载MyBatis配置 -->
    <bean id="dataSource" class="com.zaxxer.hikari.HikariDataSource">
        <property name="jdbcUrl" value="jdbc:mysql://localhost:3306/testdb"/>
        <property name="username" value="root"/>
        <property name="password" value="password"/>
        <property name="driverClassName" value="com.mysql.cj.jdbc.Driver"/>
    </bean>

    <!-- 配置 MyBatis 的 SqlSessionFactory -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"/>
        <property name="mapperLocations" value="classpath:mapper/*.xml"/>
    </bean>

    <!-- 自动扫描 com.example.api.mapper 包下的接口（Mapper），并为每个接口生成代理对象，交由 Spring 容器管理。 -->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.example.api.mapper"/>
    </bean>

    <!-- 注册 UserServiceImpl 到 Spring 容器中，并注入 userMapper -->
    <bean id="userService" class="com.example.api.service.implementation.UserServiceImpl">
        <property name="userMapper" ref="userMapper"/>
    </bean>

    <import resource="dubbo-provider.xml"/>

</beans>

.properties文件

.properties文件是一种键值对格式的文本文件。比如：

server.port=8080
spring.datasource.url=jdbc:mysql://localhost:3306/testdb
logging.level.root=INFO

1. 配置文件放在指定路径（比如 src/main/resources 目录下）
2. 启动 Spring 应用时，Spring 会自动读取这些配置文件
3. 利用 Spring 的 @Value 或 @ConfigurationProperties 注解，就能把配置值“注入”到 Java 代码里

比如：

// application.properties: app.title=xxx

@Value("${app.title}")
private String title;

当程序运行时，Spring 会把 app.title 的值 “我的Spring网站” 注入到这个 title 变量里。