Spring6-IoC(Inversion of Control)控制反转和DI(Dependency Injection)依赖注入，手动实现IOC

今天药忘吃喽~ 2023-10-12 14:09 59阅读 0赞

#### 文章目录 ####

*   *  1、Java反射
     *  2、实现Spring的IOC

### 1、Java反射 ###

`Java`反射机制是在运行状态中，对于任意一个类，都能够知道这个类的所有属性和方法；对于任意一个对象，都能够调用它的任意方法和属性；这种动态获取信息以及动态调用对象方法的功能称为`Java`语言的 反射机制 。简单来说，**反射机制指的是程序在运行时能够获取自身的信息**。

要想解剖一个类，必须先要**获取到该类的Class对象**。而剖析一个类或用反射解决具体的问题就是使用相关API **（1）java.lang.Class（2）java.lang.reflect** ，所以，**Class对象是反射的根源**。

**相关文章：**

*  [Java中的反射（通过反射获取类的结构、invoke方法、获取注解）][Java_invoke]
 *  [Java中的Reflection（反射）、暴力反射][Java_Reflection]

**自定义类**

package org.example.reflect;
    
    public class Car {
        
    
        //属性
        private String name;
        private int age;
        private String color;
    
        //无参数构造
        public Car() {
        
        }
    
        //有参数构造
        public Car(String name, int age, String color) {
        
            this.name = name;
            this.age = age;
            this.color = color;
        }
    
        //普通方法
        private void run() {
        
            System.out.println("私有方法-run.....");
        }
    
        //get和set方法
        public String getName() {
        
            return name;
        }
        public void setName(String name) {
        
            this.name = name;
        }
        public int getAge() {
        
            return age;
        }
        public void setAge(int age) {
        
            this.age = age;
        }
        public String getColor() {
        
            return color;
        }
        public void setColor(String color) {
        
            this.color = color;
        }
    
        @Override
        public String toString() {
        
            return "Car{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    ", color='" + color + '\'' +
                    '}';
        }
    }

**编写测试类**

package org.example.reflect;
    
    import org.junit.jupiter.api.Test;
    import java.lang.reflect.Constructor;
    import java.lang.reflect.Field;
    import java.lang.reflect.Method;
    
    public class TestCar {
        
    
        //1、获取Class对象多种方式
        @Test
        public void test01() throws Exception {
        
            //1 类名.class
            Class clazz1 = Car.class;
    
            //2 对象.getClass()
            Class clazz2 = new Car().getClass();
    
            //3 Class.forName("全路径")
            Class clazz3 = Class.forName("org.example.reflect.Car");
    
            //实例化
            Car car = (Car)clazz3.getConstructor().newInstance();
            System.out.println(car);
        }
    
        //2、获取构造方法
        @Test
        public void test02() throws Exception {
        
            Class clazz = Car.class;
            //获取所有构造
            // getConstructors()获取所有public的构造方法
    //        Constructor[] constructors = clazz.getConstructors();
            // getDeclaredConstructors()获取所有的构造方法public  private
            Constructor[] constructors = clazz.getDeclaredConstructors();
            for (Constructor c:constructors) {
        
                System.out.println("方法名称："+c.getName()+" 参数个数："+c.getParameterCount());
            }
    
            //指定有参数构造创建对象
            //1 构造public
    //        Constructor c1 = clazz.getConstructor(String.class, int.class, String.class);
    //        Car car1 = (Car)c1.newInstance("夏利", 10, "红色");
    //        System.out.println(car1);
            
            //2 构造private
            Constructor c2 = clazz.getDeclaredConstructor(String.class, int.class, String.class);
            c2.setAccessible(true);
            Car car2 = (Car)c2.newInstance("捷达", 15, "白色");
            System.out.println(car2);
        }
    
        //3、获取属性
        @Test
        public void test03() throws Exception {
        
            Class clazz = Car.class;
            Car car = (Car)clazz.getDeclaredConstructor().newInstance();
            //获取所有public属性
            //Field[] fields = clazz.getFields();
            //获取所有属性（包含私有属性）
            Field[] fields = clazz.getDeclaredFields();
            for (Field field:fields) {
        
                if(field.getName().equals("name")) {
        
                    //设置允许访问
                    field.setAccessible(true);
                    field.set(car,"五菱宏光");
                    System.out.println(car);
                }
                System.out.println(field.getName());
            }
        }
    
        //4、获取方法
        @Test
        public void test04() throws Exception {
        
            Car car = new Car("奔驰",10,"黑色");
            Class clazz = car.getClass();
            //1 public方法
            Method[] methods = clazz.getMethods();
            for (Method m1:methods) {
        
                //System.out.println(m1.getName());
                //执行方法 toString
                if(m1.getName().equals("toString")) {
        
                    String invoke = (String)m1.invoke(car);
                    //System.out.println("toString执行了："+invoke);
                }
            }
    
            //2 private方法
            Method[] methodsAll = clazz.getDeclaredMethods();
            for (Method m:methodsAll) {
        
                //执行方法 run
                if(m.getName().equals("run")) {
        
                    m.setAccessible(true);
                    m.invoke(car);
                }
            }
        }
    }

### 2、实现Spring的IOC ###

IoC（控制反转）和DI（依赖注入）是Spring里面核心的东西，如何实现Spring框架最核心的部分？

**①搭建模块**

搭建模块：ioc-spring

**②准备测试需要的bean**

添加依赖

<dependencies>
        
        <dependency>
            <groupId>org.junit.jupiter</groupId>
            <artifactId>junit-jupiter-api</artifactId>
            <version>5.3.1</version>
        </dependency>
    </dependencies>

创建UserDao接口

package org.example.spring6.test.dao;
    
    public interface UserDao {
        
    
        public void print();
    }

创建UserDaoImpl实现

package org.example.spring6.test.dao.impl;
    
    import org.example.spring.dao.UserDao;
    
    public class UserDaoImpl implements UserDao {
        
    
        @Override
        public void print() {
        
            System.out.println("Dao层执行结束");
        }
    }

创建UserService接口

package org.example.spring6.test.service;
    
    public interface UserService {
        
    
        public void out();
    }

创建UserServiceImpl实现类

package org.example.spring.test.service.impl;
    
    import org.example.spring.core.annotation.Bean;
    import org.example.spring.service.UserService;
    
    @Bean
    public class UserServiceImpl implements UserService {
        
    
    //    private UserDao userDao;
    
        @Override
        public void out() {
        
            //userDao.print();
            System.out.println("Service层执行结束");
        }
    }

**③定义注解**

通过注解的形式加载bean与实现依赖注入

bean注解

package org.example.spring.core.annotation;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Bean {
        
    }

依赖注入注解

package org.example.spring.core.annotation;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    @Target({
        ElementType.FIELD})
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Di {
        
    }

说明：上面两个注解可以随意取名

**④定义bean容器接口**

package org.example.spring.core;
    
    public interface ApplicationContext {
        
    
        Object getBean(Class clazz);
    }

**⑤编写注解bean容器接口实现**

`AnnotationApplicationContext`基于注解扫描bean

package org.example.spring.core;
    
    import java.util.HashMap;
    
    public class AnnotationApplicationContext implements ApplicationContext {
        
    
        //存储bean的容器
        private HashMap<Class, Object> beanFactory = new HashMap<>();
    
        @Override
        public Object getBean(Class clazz) {
        
            return beanFactory.get(clazz);
        }
    
        /**
         * 根据包扫描加载bean
         * @param basePackage
         */
        public AnnotationApplicationContext(String basePackage) {
        
            
        }
    }

**⑥编写扫描bean逻辑**

通过构造方法传入包的base路径，扫描被`@Bean(自己定义的)`注解的java对象，完整代码如下：

package org.example.spring.core;
    
    import org.example.spring.core.annotation.Bean;
    
    import java.io.File;
    import java.util.HashMap;
    
    public class AnnotationApplicationContext implements ApplicationContext {
        
    
        //存储bean的容器
        private HashMap<Class, Object> beanFactory = new HashMap<>();
        private static String rootPath;
    
        @Override
        public Object getBean(Class clazz) {
        
            return beanFactory.get(clazz);
        }
    
        /**
         * 根据包扫描加载bean
         * @param basePackage
         */
        public AnnotationApplicationContext(String basePackage) {
        
           try {
        
                String packageDirName = basePackage.replaceAll("\\.", "\\\\");
                Enumeration<URL> dirs =Thread.currentThread().getContextClassLoader().getResources(packageDirName);
                while (dirs.hasMoreElements()) {
        
                    URL url = dirs.nextElement();
                    String filePath = URLDecoder.decode(url.getFile(),"utf-8");
                    rootPath = filePath.substring(0, filePath.length()-packageDirName.length());
                    loadBean(new File(filePath));
                }
    
            } catch (Exception e) {
        
                throw new RuntimeException(e);
            }
        }
    
        private  void loadBean(File fileParent) {
        
            if (fileParent.isDirectory()) {
        
                File[] childrenFiles = fileParent.listFiles();
                if(childrenFiles == null || childrenFiles.length == 0){
        
                    return;
                }
                for (File child : childrenFiles) {
        
                    if (child.isDirectory()) {
        
                        //如果是个文件夹就继续调用该方法,使用了递归
                        loadBean(child);
                    } else {
        
                        //通过文件路径转变成全类名,第一步把绝对路径部分去掉
                        String pathWithClass = child.getAbsolutePath().substring(rootPath.length() - 1);
                        //选中class文件
                        if (pathWithClass.contains(".class")) {
        
                            //    com.xinzhi.dao.UserDao
                            //去掉.class后缀，并且把 \ 替换成 .
                            String fullName = pathWithClass.replaceAll("\\\\", ".").replace(".class", "");
                            try {
        
                                Class<?> aClass = Class.forName(fullName);
                                //把非接口的类实例化放在map中
                                if(!aClass.isInterface()){
        
                                    Bean annotation = aClass.getAnnotation(Bean.class);
                                    if(annotation != null){
        
                                        Object instance = aClass.newInstance();
                                        //判断一下有没有接口
                                        if(aClass.getInterfaces().length > 0) {
        
                                            //如果有接口把接口的class当成key，实例对象当成value
                                            System.out.println("正在加载【"+ aClass.getInterfaces()[0] +"】,实例对象是：" + instance.getClass().getName());
                                            beanFactory.put(aClass.getInterfaces()[0], instance);
                                        }else{
        
                                            //如果有接口把自己的class当成key，实例对象当成value
                                            System.out.println("正在加载【"+ aClass.getName() +"】,实例对象是：" + instance.getClass().getName());
                                            beanFactory.put(aClass, instance);
                                        }
                                    }
                                }
                            } catch (ClassNotFoundException | IllegalAccessException | InstantiationException e) {
        
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        }
    
    }

**⑦java类标识Bean注解**

@Bean
    public class UserServiceImpl implements UserService

@Bean
    public class UserDaoImpl implements UserDao

**⑧测试Bean加载**

package org.example.spring;
    
    import org.example.spring.core.AnnotationApplicationContext;
    import org.example.spring.core.ApplicationContext;
    import org.example.spring.test.service.UserService;
    import org.junit.jupiter.api.Test;
    
    public class SpringIocTest {
        
    
        @Test
        public void testIoc() {
        
            ApplicationContext applicationContext = new AnnotationApplicationContext("org.example.spring.test");
            UserService userService = (UserService)applicationContext.getBean(UserService.class);
            userService.out();
            System.out.println("run success");
        }
    }

控制台打印测试

**⑨依赖注入**

只要userDao.print();调用成功，说明就注入成功

package org.example.spring.test.service.impl;
    
    import org.example.spring.core.annotation.Bean;
    import org.example.spring.core.annotation.Di;
    import org.example.spring.dao.UserDao;
    import org.example.spring.service.UserService;
    
    @Bean
    public class UserServiceImpl implements UserService {
        
    
        @Di
        private UserDao userDao;
    
        @Override
        public void out() {
        
            userDao.print();
            System.out.println("Service层执行结束");
        }
    }

执行第八步：报错了，说明当前userDao是个空对象，还没有进行注入

**⑩依赖注入实现**

package org.example.spring.core;
    
    import org.example.spring.core.annotation.Bean;
    import org.example.spring.core.annotation.Di;
    
    import java.io.File;
    import java.lang.reflect.Field;
    import java.util.HashMap;
    import java.util.Map;
    
    public class AnnotationApplicationContext implements ApplicationContext {
        
    
        //存储bean的容器
        private HashMap<Class, Object> beanFactory = new HashMap<>();
        private static String rootPath;
    
        @Override
        public Object getBean(Class clazz) {
        
            return beanFactory.get(clazz);
        }
    
        /**
         * 根据包扫描加载bean
         * @param basePackage
         */
        public AnnotationApplicationContext(String basePackage) {
        
            try {
        
                String packageDirName = basePackage.replaceAll("\\.", "\\\\");
                Enumeration<URL> dirs =Thread.currentThread().getContextClassLoader().getResources(packageDirName);
                while (dirs.hasMoreElements()) {
        
                    URL url = dirs.nextElement();
                    String filePath = URLDecoder.decode(url.getFile(),"utf-8");
                    rootPath = filePath.substring(0, filePath.length()-packageDirName.length());
                    loadBean(new File(filePath));
                }
    
            } catch (Exception e) {
        
                throw new RuntimeException(e);
            }
            
            //依赖注入
            loadDi();
        }
        
        private  void loadBean(File fileParent) {
        
            if (fileParent.isDirectory()) {
        
                File[] childrenFiles = fileParent.listFiles();
                if(childrenFiles == null || childrenFiles.length == 0){
        
                    return;
                }
                for (File child : childrenFiles) {
        
                    if (child.isDirectory()) {
        
                        //如果是个文件夹就继续调用该方法,使用了递归
                        loadBean(child);
                    } else {
        
                        //通过文件路径转变成全类名,第一步把绝对路径部分去掉
                        String pathWithClass = child.getAbsolutePath().substring(rootPath.length() - 1);
                        //选中class文件
                        if (pathWithClass.contains(".class")) {
        
                            //    com.xinzhi.dao.UserDao
                            //去掉.class后缀，并且把 \ 替换成 .
                            String fullName = pathWithClass.replaceAll("\\\\", ".").replace(".class", "");
                            try {
        
                                Class<?> aClass = Class.forName(fullName);
                                //把非接口的类实例化放在map中
                                if(!aClass.isInterface()){
        
                                    Bean annotation = aClass.getAnnotation(Bean.class);
                                    if(annotation != null){
        
                                        Object instance = aClass.newInstance();
                                        //判断一下有没有接口
                                        if(aClass.getInterfaces().length > 0) {
        
                                            //如果有接口把接口的class当成key，实例对象当成value
                                            System.out.println("正在加载【"+ aClass.getInterfaces()[0] +"】,实例对象是：" + instance.getClass().getName());
                                            beanFactory.put(aClass.getInterfaces()[0], instance);
                                        }else{
        
                                            //如果有接口把自己的class当成key，实例对象当成value
                                            System.out.println("正在加载【"+ aClass.getName() +"】,实例对象是：" + instance.getClass().getName());
                                            beanFactory.put(aClass, instance);
                                        }
                                    }
                                }
                            } catch (ClassNotFoundException | IllegalAccessException | InstantiationException e) {
        
                                e.printStackTrace();
                            }
                        }
                    }
                }
            }
        }
    
        private void loadDi() {
        
            for(Map.Entry<Class,Object> entry : beanFactory.entrySet()){
        
                //就是咱们放在容器的对象
                Object obj = entry.getValue();
                Class<?> aClass = obj.getClass();
                Field[] declaredFields = aClass.getDeclaredFields();
                for (Field field : declaredFields){
        
                    Di annotation = field.getAnnotation(Di.class);
                    if( annotation != null ){
        
                        field.setAccessible(true);
                        try {
        
                            System.out.println("正在给【"+obj.getClass().getName()+"】属性【" + field.getName() + "】注入值【"+ beanFactory.get(field.getType()).getClass().getName() +"】");
                            field.set(obj,beanFactory.get(field.getType()));
                        } catch (IllegalAccessException e) {
        
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    
    }

执行第八步：测试依赖注入，执行成功

[Java_invoke]: https://xy5462.blog.csdn.net/article/details/130549345
[Java_Reflection]: https://xy5462.blog.csdn.net/article/details/130470675