简单手写Spring IOC容器,实现依赖注入

如何简单手写IOC容器

代码地址:https://github.com/zhangbaoss/spring-ioc

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();
}