如何手写IOC容器

一、准备工作

1.配置文件中添加扫描包路径

applicationContext.xml文件中添加扫描包路径

<context:component-scan base-package="com.zhangbaoss"/>

2.实现自己的注解类

@ExtController

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface ExtController {
	String value() default "";
}

二、获取扫描包下所有类(ClassUtils.java)

List<String> classes = ClassUtils.getClassesFormPackage(path);

1.根据配置文件路径获取配置文件中需要扫描的包名

packageName = getPackageName(xmlPath);

2.获取需要扫描的包的路径

String packagePath = getPackagePath();

3.将需要扫描的包下的所有类放入集合中

getClassForPath(new File(packagePath), getPath());

三、查看类上是否有特定注解并初始化map

initClassMap(classes);

initClassMap(List classes)

private void initClassMap(List<String> classes) throws Exception {
	for (String className : classes) {
		Class clazz = Class.forName(className);
		if (clazz.isAnnotationPresent(ExtController.class)) {
			String value = ((ExtController) clazz.getAnnotation(ExtController.class)).value();
			classMapPutValue(value, className, clazz);
		} else if (clazz.isAnnotationPresent(ExtService.class)) {
			String value = ((ExtService) clazz.getAnnotation(ExtService.class)).value();
			classMapPutValue(value, className, clazz);
		} else if (clazz.isAnnotationPresent(ExtRepository.class)) {
			String value = ((ExtRepository) clazz.getAnnotation(ExtRepository.class)).value();
			classMapPutValue(value, className, clazz);
		} else if (clazz.isAnnotationPresent(ExtComponent.class)) {
			String value = ((ExtComponent) clazz.getAnnotation(ExtComponent.class)).value();
			classMapPutValue(value, className, clazz);
		}
	}
}

四、初始化字段值

initField();

initField()

private void initField() throws IllegalAccessException {
	Set<Map.Entry<String, Object>> entries = classMap.entrySet();
	for (Map.Entry<String, Object> entity : entries) {
		Object object = entity.getValue();
		Field[] fields = entity.getValue().getClass().getDeclaredFields();
		if (fields != null && fields.length > 0) {
			//注入对象
			for (Field field : fields) {
				if (field.isAnnotationPresent(ExtAutowired.class)) {
					//设置private字段可赋值
					field.setAccessible(true);
					field.set(object, classMap.get(field.getName()));
				}
			}
		}
	}
}

五、测试方法

public static void main(String[] args) throws Exception {
	ExtClassPathXmlApplicationContext app =
			new ExtClassPathXmlApplicationContext("applicationContext.xml");
	SpringIocXmlController springIocXmlController =
			(SpringIocXmlController) app.getBean("springIocXmlController");
	springIocXmlController.test();
}