手写 Spring 之 Autowired、Component、ComponentScan 注解功能模拟

深藏阁楼爱情的钟 2023-09-29 10:11 13阅读 0赞

#### 手写 Spring 之 Autowired、Component、ComponentScan 注解功能模拟 ####

*  一、创建一个空的项目
 *  二、代码说明
 *   *  容器定义
     *  注解
     *   *  1.Autowired
         *  2.Component
         *  3.ComponentScan
         *  4.Scope
     *  测试实体
     *   *  1.Student
         *  2.Teacher
         *  3.User
     *  启动类
     *   *  1.AppConfig
     *  测试类
     *   *  1.Test
 *  三、结果

## 一、创建一个空的项目 ##

完成后的工程目录如图：  
![在这里插入图片描述][watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA54yq5oKf6YGT_size_16_color_FFFFFF_t_70_g_se_x_16]

## 二、代码说明 ##

### 容器定义 ###

package com.demo.spring;
    
    
    import com.demo.spring.ann.Autowired;
    import com.demo.spring.ann.Component;
    import com.demo.spring.ann.ComponentScan;
    import com.demo.spring.ann.Scope;
    
    import java.beans.Introspector;
    import java.io.File;
    import java.lang.reflect.Field;
    import java.net.URL;
    import java.util.HashMap;
    import java.util.Map;
    
    /**
     * Description: Spring 容器
     *
     * @Author: zhx & moon hongxu_1234@163.com
     * @Date: 2022-04-13 20:06
     * @version: V1.0.0
     */
    public class SpringApplicationContext {
        
    
        /**
         * 启动类
         */
        private Class appClass;
    
        /**
         * 扫描结果池
         */
        private static Map<String,BeanDefinition> beanMap = new HashMap<>(16);
    
        /**
         * 单例池
         */
        private static Map<String,Object> singletonMap = new HashMap<>(16);
    
        /**
         * 构造容器 扫描注解并实例化Bean
         * @param appClass
         */
        public SpringApplicationContext(Class appClass)  {
        
            this.appClass = appClass;
            //扫描
            scan();
            //生成
            for (String k:beanMap.keySet()){
        
                singletonMap.put(k,createBean(k, beanMap.get(k)));
            }
        }
    
        /**
         * 获取Bean实例 不存在则抛出空指针异常
         * @param beanName
         * @return
         */
        public Object getBean(String beanName){
        
            if (beanMap.containsKey(beanName)){
        
                BeanDefinition beanDefinition = beanMap.get(beanName);
                if ("prototype".equals(beanDefinition.getScope())){
        
                    return createBean(beanName,beanDefinition);
                }else{
        
                    return singletonMap.get(beanName);
                }
            }
            throw new NullPointerException();
        }
    
    
        /**
         * 扫描需要在启动时生成Bean配置的类
         */
        private void scan(){
        
            if (appClass.isAnnotationPresent(ComponentScan.class)){
        
                ComponentScan scan = (ComponentScan) appClass.getAnnotation(ComponentScan.class);
                String scanPath = scan.value();
                scanPath = scanPath.replace(".","/");
                ClassLoader classLoader = SpringApplicationContext.class.getClassLoader();
                URL url = classLoader.getResource(scanPath);
                File file = new File(url.getFile());
                //实际可能需要递归处理
                if (file.isDirectory()){
        
                    for (File f:file.listFiles()){
        
                        String absolutePath = f.getAbsolutePath();
                        absolutePath = absolutePath.substring(absolutePath.indexOf("com"),absolutePath.indexOf(".class")).replace("\\",".");
                        try {
        
                            Class clazz = classLoader.loadClass(absolutePath);
                            if (clazz.isAnnotationPresent(Component.class)){
        
                                //获取Bean名称
                                Component component = (Component) clazz.getAnnotation(Component.class);
                                String beanName = component.value();
                                if ("".equals(beanName)){
        
                                    beanName = Introspector.decapitalize(clazz.getSimpleName());
                                }
                                BeanDefinition beanDefinition = new BeanDefinition();
                                beanDefinition.setScope("");
                                beanDefinition.setType(clazz);
                                //判断单例还是原型（多例）
                                if (clazz.isAnnotationPresent(Scope.class)){
        
                                    Scope scope = (Scope) clazz.getAnnotation(Scope.class);
                                    String model = scope.value();
                                    if ("prototype".equals(model)){
        
                                        beanDefinition.setScope("prototype");
                                    }
                                }
                                beanMap.put(beanName,beanDefinition);
                            }
                        } catch (ClassNotFoundException e) {
        
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    
        /**
         * 创建Bean 当前只处理无参构造
         * @return
         */
        public Object createBean(String beanName,BeanDefinition beanDefinition){
        
            Class clazz = beanDefinition.getType();
            try {
        
                Object bean = clazz.getConstructor().newInstance();
                for (Field field:clazz.getDeclaredFields()){
        
                    if (field.isAnnotationPresent(Autowired.class)){
        
                        String autowiredBeanName = field.getName();
                        field.setAccessible(true);
                        field.set(bean,getBean(autowiredBeanName));
                    }
                }
                return bean;
            } catch (Exception e) {
        
                e.printStackTrace();
            }
            return null;
        }
    }

### 注解 ###

#### 1.Autowired ####

package com.demo.spring.ann;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    /**
     * Description: 依赖注入注解
     *
     * @Author: zhx & moon hongxu_1234@163.com
     * @Date: 2022-04-13 22:32
     * @version: V1.0.0
     */
    @Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Autowired {
        
    
    }

#### 2.Component ####

package com.demo.spring.ann;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    /**
     * Description: 配置类注解
     *
     * @Author: zhx & moon hongxu_1234@163.com
     * @Date: 2022-04-13 20:19
     * @version: V1.0.0
     */
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Component {
        
    
        String value() default "";
    
    }

#### 3.ComponentScan ####

package com.demo.spring.ann;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    /**
     * Description: 注解扫描
     *
     * @Author: zhx & moon hongxu_1234@163.com
     * @Date: 2022-04-13 22:30
     * @version: V1.0.0
     */
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface ComponentScan {
        
    
        String value() default "";
    
    }

#### 4.Scope ####

package com.demo.spring.ann;
    
    import java.lang.annotation.ElementType;
    import java.lang.annotation.Retention;
    import java.lang.annotation.RetentionPolicy;
    import java.lang.annotation.Target;
    
    /**
     * Description: 作用域
     *
     * @Author: zhx & moon hongxu_1234@163.com
     * @Date: 2022-04-13 23:05
     * @version: V1.0.0
     */
    @Target(ElementType.TYPE)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface Scope {
        
    
        String value() default "";
    
    }

### 测试实体 ###

#### 1.Student ####

package com.demo.test.entity;
    
    import com.demo.spring.ann.Component;
    import com.demo.spring.ann.Scope;
    
    /**
     * Description: 学生
     *
     * @Author: zhx & moon hongxu_1234@163.com
     * @Date: 2022-04-13 23:43
     * @version: V1.0.0
     */
    @Component
    @Scope("prototype")
    public class Student {
        
    
    }

#### 2.Teacher ####

package com.demo.test.entity;
    
    import com.demo.spring.ann.Component;
    
    /**
     * Description: 老师
     *
     * @Author: zhx & moon hongxu_1234@163.com
     * @Date: 2022-04-13 23:48
     * @version: V1.0.0
     */
    @Component
    public class Teacher {
        
    }

#### 3.User ####

package com.demo.test.entity;
    
    import com.demo.spring.ann.Autowired;
    import com.demo.spring.ann.Component;
    
    /**
     * Description: 测试实体
     *
     * @Author: zhx & moon hongxu_1234@163.com
     * @Date: 2022-04-13 22:31
     * @version: V1.0.0
     */
    @Component("user")
    public class User {
        
    
        @Autowired
        Teacher teacher;
    
        public void test(){
        
            System.out.println("张三");
            System.out.println(teacher);
        }
    
    }

### 启动类 ###

#### 1.AppConfig ####

package com.demo.test;
    
    import com.demo.spring.ann.ComponentScan;
    
    /**
     * Description: 启动类
     *
     * @Author: zhx & moon hongxu_1234@163.com
     * @Date: 2022-04-13 22:35
     * @version: V1.0.0
     */
    @ComponentScan("com.demo.test.entity")
    public class AppConfig {
        
    
    }

### 测试类 ###

#### 1.Test ####

package com.demo.test;
    
    import com.demo.spring.SpringApplicationContext;
    import com.demo.test.entity.User;
    
    /**
     * Description: 测试类
     *
     * @Author: zhx & moon hongxu_1234@163.com
     * @Date: 2022-04-13 20:04
     * @version: V1.0.0
     */
    public class Test {
        
        public static void main(String[] args) {
        
    
            SpringApplicationContext applicationContext = new SpringApplicationContext(AppConfig.class);
            System.out.println("单例--------------------");
            System.out.println(applicationContext.getBean("user"));
            System.out.println(applicationContext.getBean("user"));
            System.out.println(applicationContext.getBean("user"));
            System.out.println("原型--------------------");
            System.out.println(applicationContext.getBean("student"));
            System.out.println(applicationContext.getBean("student"));
            System.out.println("注入--------------------");
            System.out.println(applicationContext.getBean("teacher"));
            User user = (User) applicationContext.getBean("user");
            user.test();
        }
    }

## 三、结果 ##

Connected to the target VM, address: '127.0.0.1:52335', transport: 'socket'
    Java HotSpot(TM) 64-Bit Server VM warning: Sharing is only supported for boot loader classes because bootstrap classpath has been appended
    单例--------------------
    com.demo.test.entity.User@27fa135a
    com.demo.test.entity.User@27fa135a
    com.demo.test.entity.User@27fa135a
    原型--------------------
    com.demo.test.entity.Student@46f7f36a
    com.demo.test.entity.Student@421faab1
    注入--------------------
    com.demo.test.entity.Teacher@2b71fc7e
    张三
    com.demo.test.entity.Teacher@2b71fc7e
    Disconnected from the target VM, address: '127.0.0.1:52335', transport: 'socket'
    
    Process finished with exit code 0

[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA54yq5oKf6YGT_size_16_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/1cfd4e57d115445a8ce06bf3889221cf.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA54yq5oKf6YGT,size_16,color_FFFFFF,t_70,g_se,x_16