1 Spring程序开发步骤
①导入 Spring 开发的基本包坐标
②编写 Dao 接口和实现类
③创建 Spring 核心配置文件
④在 Spring 配置文件中配置 UserDaoImpl
⑤使用 Spring 的 API 获得 Bean 实例
注意事项：
之后无法注入
2 导入Spring开发的基本包坐标
<properties> <spring.version>5.0.5.RELEASE</spring.version> </properties> <!--导入spring的context坐标，context依赖core、beans、expression--> <dependencies> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>${spring.version}</version> </dependency> </dependencies>
3 编写Dao接口和实现类
public interface UserDao { public void save(); }
public class UserDaoImpl implements UserDao { public void save() { System.out.println("UserDao save method running...."); } }
4 创建Spring核心配置文件
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> </beans>
5 在Spring配置文件中配置UserDaoImpl
<bean id="userDao" class="com.zgl.dao.impl.UserDaoImpl"></bean>
6 使用Spring的API获得Bean实例
package com.zgl.demo; import com.zgl.dao.UserDao; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class UserDaoDemo { public static void main(String[] args) { ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml"); UserDao userDao = (UserDao) applicationContext.getBean("userDao"); userDao.save(); } }
7 项目结构
8 运行效果
9 Spring注解之@Autowired：Setter 方法上使用@Autowired注解
可以在 JavaBean中的 setter 方法中使用 @Autowired 注解。当 Spring遇到一个在 setter 方法中使用的 @Autowired 注解时，它会在方法中按照类型自动装配参数值。创建测试类User，并且添加属性student，
import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Component; import java.io.Serializable; /** * @author oldlu */ @Component public class User implements Serializable { private static final long serialVersionUID = 6089103683553156328L; private Long id; private Student student; public Student getStudent() { return student; } @Autowired public void setStudent(Student student) { this.student = student; } public void isStu() { student.studentStudy(); System.out.println("------ 装配Bean成功 ---------"); } }
下面创建依赖的类文件 Student.java，切莫忘记在类文件上添加注解 @Component：
import lombok.Getter; import lombok.Setter; import org.springframework.stereotype.Component; import java.io.Serializable; import java.util.Date; /** * @author oldlu */ @Getter @Setter @Component public class Student implements Serializable { private static final long serialVersionUID = -5246589941647210011L; //姓名 private String name; public Student() { System.out.println("A default student constructor." ); } public void studentStudy() { System.out.println("A student is studying." ); } }
修改Spring Boot启动类，通过Spring容器拿到Bean实例user：
import com.east7.bean.User; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.context.ApplicationContext; /** * @author oldlu */ @SpringBootApplication public class East7Application { public static void main(String[] args) { ApplicationContext act = SpringApplication.run(East7Application.class, args); User user = (User) act.getBean("user"); user.isStu(); } }
启动应用程序，控制台将会输出以下消息：
A default student constructor. A student is studying. ------ 装配Bean成功 ---------
说明student属性被装配成功。如果setStudent方法不加注解，程序运行时，会抛出如下异常：
Exception in thread "main" java.lang.NullPointerException at com.east7.bean.User.isStu(User.java:28) at com.east7.East7Application.main(East7Application.java:25)
