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手写Sping IOC（基于Setter方法注入）

news 来源：原创 2024/5/19 2:39:15

什么是IOC? 控制反转:把对象的创建和对象之间的调用过程,从程序员手里转交给Spring进行管理。

1.导入依赖

<dependency>
    <groupId>org.dom4j</groupId>
    <artifactId>dom4j</artifactId>
    <version>2.1.3</version>
</dependency>
<dependency>
    <groupId>jaxen</groupId>
    <artifactId>jaxen</artifactId>
    <version>1.2.0</version>
</dependency>
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.13.2</version>
</dependency>
<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.6</version>
</dependency>

2.编写spring ioc接口

public interface ApplicationContext{

  getBean(String beanName);
}

3.实现soring ioc接口

public class ClassPathXmlApplicationContext implements ApplicationContext{
  
  private final Map<String, Object> objectMap = new HashMap<>();	

  public ClassPathXmlApplicationContext(String springConfigXml){
  	try {
            InputStream inputStream = Thread.currentThread().getContextClassLoader().getResourceAsStream(springConfigXml);
            SAXReader reader = new SAXReader();
            Document document = reader.read(inputStream);
            List<Node> nodes = document.selectNodes("//bean");
            //读取bean标签创建bean对象,bean存入Map中
            for (Node node : nodes) {
                Element element = (Element) node;
                String id = element.attributeValue("id");
                String className = element.attributeValue("class");
                Class<?> clazz = Class.forName(className);
                Object obj = clazz.newInstance();
                objectMap.put(id, obj);
            }

            //读取bean标签下的property标签
            for (Node node : nodes) {
                Element element = (Element) node;
                String id = element.attributeValue("id");
                String className = element.attributeValue("class");
                Class<?> clazz = Class.forName(className);
                List<Element> property = element.elements("property");
                for (Element elem : property) {
                    String ref = elem.attributeValue("ref");
                    String name = elem.attributeValue("name");
                    //将property对象设置到父级bean对象
                    String setMethod = "set" + name.toUpperCase().charAt(0) + name.substring(1);
                    Method method = clazz.getDeclaredMethod(setMethod, objectMap.get(ref).getClass());
                    method.invoke(objectMap.get(id), objectMap.get(ref));
                }
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
  }

  @Override
  public Object getBean(String beanId) {
    return objectMap.get(beanId);
  }
}

4.配置下xml(bean.xml)

<?xml version="1.0" encoding="UTF-8" ?>
<beans>

    <bean id="userController" class="com.xxx.yyy.controller.UserControllr">
        <property name="userService" ref="userService"/>
    </bean>

    <bean id="userService" class="com.xxx.yyy.service.impl.UserServiceImpl">
        <property name="userMapper" ref="userMapper"/>
    </bean>

    <bean id="userMapper" class="com.xxx.yyy.mapper.UserMapper"/>
</beans>

5.测试

public class SpringIocTest{

    @Test
    public void iocTest(){
      ApplicationContext context=new ClassPathXmlApplication("bean.xml");
      UserController userController=context.getBean("userController");
      userController.getUser(1);
    }
}

结果:
Connected to the target VM, address: '127.0.0.1:36341', transport: 'socket'
User(id=1, name=张三, sex=男, age=58, addr=中国)
Disconnected from the target VM, address: '127.0.0.1:36341', transport: 'socket'

Process finished with exit code 0

6.需要的类与接口

(User.class,UserController.class,UserService.interface,UserServiceImpl.class,UserMapper.class)

//User.class
@Data
public class User{

  private Integer id;

  private String name;

  private String sex;

  private Integer age;

  private String addr;
}

//UserController.class
public class UserController{

  private UserService userService;

  public void setUserService(UserServiceImpl userServiceImpl){
    this.userService=userServiceImpl;
  }

  public User getUser(Integer userId){
	return userService.getUser(userId);
  }
}

//UserService.interface
public interface UserService{
  
  User getUser(Integer userId);
}

//UserServiceImpl.class
public UserServiceImpl implements UserService{

  @Setter
  private UserMapper userMapper;

  public User getUser(Integer userId){
    return userMapper.getUser(userId);
  }
}

//UserMapper.class  (这里只做测试，就不去具体实现mybatis与Mapper的映射了)
public UserMapper{

  User getUser(Integer userId){
    User user=new User();
    user.setId(userId);
    user.setName("张三");
    user.setSex("男");
    user.setAge("58");
    user.setAddr("中国");
    return user;
  }
}

7.反射机制

获取class

Object obj = new Object();
Class<?> clazz1 = Class.forName("com.xxx.yyy.ClassName");
Class<?> clazz2 = ClassName.class;
Class<?> clazz3 = obj.getClass();

获取构造方法

Constructor con = clazz.getConstructor()

创建对象

1.无参构造创建

Object obj = clazz.newInstance();

2.有参数构造创建

Class[] parameterTypes = {String.class,int.class,char.class};
Constructor con = clazz.getConstructor(parameterTypes);
Object obj = con.newIntstance(parameterTypes);

获取Field

getField() 与 getDeclaredField() 区别：
getField() 获取所有 public 的属性包括继承的 public 属性,
getDeclaredField() 获取当前类的所有属性，包括 private 修饰的属性，但是在访问 private 属性时，设置 setAccessible(true) 才可以访问.

Field[] fields = clazz.getDeclaredFields()
Field field = clazz.getDeclaredFiled("fieldName");
//取值
Object value = field.get(obj);

获取method

getMethod()与getDeclaredMethod()区别：
getMethod()调用所有public的方法包括继承的public方法,
getDeclaredField()调用当前类的所有方法，包括private修饰的方法，但是在调用private方法时，设置setAccessible(true)才可以调用.

//无参  
Method[] methods=clazz.getDeclaredMethods()
Method method=clazz.getDeclaredMethod("methodName");//如getName()
method.setAccessible(true);
method.invoke(obj);//如getName(), Obejct value = method.invoke(obj)

//有参
Method method=clazz.getDeclaredMethod("methodName",methodParamTypes.class);//如User类setName(String name)
method.setAccessible(true);
method.invoke(obj, value);//如User类setName(String name)方法 obj=User,value="张三"