静态工具类中使用@Autowired的方法

静态工具类中使用@Autowired的方法

在Spring项目中我习惯使用@Autowired来注入Service层或者Dao层，在一次偶然我在静态方法中查询数据库数据，而报了NullPointerException，一路找来发现Mapper为Null，分析原因发现Spring不支持依赖注入static静态变量，静态变量/类变量不是对象的属性而是一个类的属性，spring则是基于对象层面上的依赖注入，好了不罗嗦了，下面给出解决方案直接上代码。

静态工具类：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;

/**
 * @Author: Wenx
 * @Description: 静态工具类中使用@Autowired的方法
 * @Date: Created in 2020/1/13 20:29
 * @Modified By：
 */
@Component
public class DaoUtils {
    private static final Logger logger = LoggerFactory.getLogger(DaoUtils.class);
    private static DaoUtils utils;

    @Autowired
    private TestMapper testMapper;

    @PostConstruct
    public void init() {
        utils = this;
    }

    public static TestDO getTest(Integer id) {
        TestDO testDO = utils.testMapper.selectTestById(1);
        return testDO;
    }

}

Mapper：

import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;
import org.apache.ibatis.annotations.Select;
import org.springframework.stereotype.Repository;

/**
 * @Author: Wenx
 * @Description:
 * @Date: Created in 2020/1/13 20:32
 * @Modified By：
 */
@Mapper
@Repository
public interface TestMapper {

    /**
     * 查询table_test表记录
     *
     * @param id ID
     * @return TestDO
     */
    @Select("select id,name from table_test where id = #{id}")
    TestDO selectTestById(@Param("id") Integer id);

}

实体：

/**
 * @Author: Wenx
 * @Description:
 * @Date: Created in 2020/1/13 20:35
 * @Modified By：
 */
public class TestDO {

    private Integer id;
    private String name;


    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;
    }

}

启动类：

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ApplicationContext;

/**
 * @Author: Wenx
 * @Description: 启动类
 * @Date: Created in 2020/1/13 20:13
 * @Modified By：
 */
@SpringBootApplication
public class StudyDemoApplication {
    private static final Logger logger = LoggerFactory.getLogger(StudyDemoApplication.class);

    public static void main(String[] args) {
        ApplicationContext context = SpringApplication.run(StudyDemoApplication.class, args);

        TestDO testDO = DaoUtils.getTest(1);
    }
}