简单手写Spring依赖注入@Value和@Resource底层实现

港控/mmm° 2022-10-22 14:54 209阅读 0赞

### 简单手写Spring依赖注入@Value和@Resource底层实现 ###

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这里我们简单实现一下spring中的 @Value() 和 @Resource()

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@MyValue 注解（@Value()）：

@Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface MyValue { 
        String value();
    }

@MyComponent注解（@Resource()）:

@Target(ElementType.FIELD)
    @Retention(RetentionPolicy.RUNTIME)
    public @interface MyComponent { 
        Class value();
    }

CPU接口及实现类：

public interface CPU { 
        void run();
    }
    
    public class AMDCPU implements CPU { 
        public void run() { 
            System.out.println("AMDCUP跑起来了");
        }
    }

内存接口及实现类：

public interface Memory { 
        void read();
        void write();
    }
    
    public class KingstonMemory implements Memory { 
        public void read() { 
            System.out.println("金士顿内存读取");
        }
    
        public void write() { 
            System.out.println("金士顿内存写入");
        }
    }

需要注入属性的computer类：

public class Computer { 
    
        @MyValue("苹果")
        private String brand;
        @MyComponent(AMDCPU.class)
        private CPU cpu;
        @MyComponent(KingstonMemory.class)
        private Memory memory;
    
        public void start(){ 
            System.out.println(brand+"的电脑开启");
            cpu.run();
            memory.read();
            memory.write();
        }
    
        public String getBrand() { 
            return brand;
        }
    
        public void setBrand(String brand) { 
            this.brand = brand;
        }
    
        public CPU getCpu() { 
            return cpu;
        }
    
        public void setCpu(CPU cpu) { 
            this.cpu = cpu;
        }
    
        public Memory getMemory() { 
            return memory;
        }
    
        public void setMemory(Memory memory) { 
            this.memory = memory;
        }
    }

`重点来了 spring底层利用反射机制实现`

创建一个工厂 ComputerFactory：

public class ComputerFactory { 
        public static Computer getComputer() throws IllegalAccessException, InstantiationException { 
            Class<Computer> computerClass = Computer.class;
            Computer obj = computerClass.newInstance();
    
            Field[] fields = computerClass.getDeclaredFields();
            for (Field field : fields) { 
                field.setAccessible(true);
    
                MyValue myValue = field.getDeclaredAnnotation(MyValue.class);
                if (myValue!=null){ 
                    String value = myValue.value();
                    field.set(obj,value);
                }
                MyComponent myComponent = field.getDeclaredAnnotation(MyComponent.class);
                if(myComponent!=null){ 
                    Class value = myComponent.value();
                    Object o = value.newInstance();
                    field.set(obj,o);
                }
            }
            return obj;
        }
    }

测试类;

public class Test { 
        public static void main(String[] args) throws InstantiationException, IllegalAccessException { 
            Computer computer = ComputerFactory.getComputer();
            computer.start();
        }
    }

效果：可以发现注入到工厂创建出的computer类中了  
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