手写SpingIOC（基于Setter方法注入）

 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

org.dom4jdom4j2.1.3

jaxenjaxen1.2.0

junitjunit4.13.2

org.projectlomboklombok1.18.6


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

4.配置下xml(bean.xml)

5.测试

public class SpringIocTest{@Testpublic void iocTest(){ApplicationContext cOntext=new ClassPathXmlApplication("bean.xml");UserController userCOntroller=context.getBean("userController");userController.getUser(1);}
}

结果:
Connected to the target VM, address: &＃39;127.0.0.1:36341&＃39;, transport: &＃39;socket&＃39;
User(id=1, name=张三, sex=男, age=58, addr=中国)
Disconnected from the target VM, address: &＃39;127.0.0.1:36341&＃39;, transport: &＃39;socket&＃39;

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{@Setterprivate 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

相关类

•   Class 类的类
•   Field 属性
•   Method 方法
•   Constructor 构造方法

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"