标签：substring bsp shm exist users end this targe element
IOC：控制反转。原先是程序员控制Java对象的创建，JVM GC负责Java对象的销毁，控制权在程序员手中。现在Java Bean的
实例对象由IOC容器负责创建、销毁，程序员反而是无需关心Bean的生命周期。这就是控制反转。
原理：内存中建立一个currentHashMap当作容器（考虑到多线程），采用（BeanID/BeanName,statance）形式存储Bean。
bean的建立在容器启动之后会通过Java反射来创建对象实例（通过注解、XML），然后放入容器中。依赖注入（一个bean中
含有其他bean）可以通过反射获取beanName/ID,然后遍历容器，获取到对应的Bean。
手动写简易实现：
目录图：
SelfAutowired：
@Target({ElementType.FIELD,ElementType.METHOD,ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface SelfAutowired {
}
SelfService：
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface SelfService {
}
SelfPathXmlApplicationContext：
public class SelfPathXmlApplicationContext {
/**
* 包名
*/
private String packageName;
//IOC容器
private ConcurrentHashMap<String, Object> beans = null;
public SelfPathXmlApplicationContext(String packageName) throws Exception {
System.out.println("容器类正在初始化");
beans = new ConcurrentHashMap<String, Object>();
this.packageName = packageName;
initBeans();
initEntryField();
Arrays.asList(1,2,3);
}
/**
* Description: 初始化所有的Bean
*
* @param
* @return void
* @date 9:44 2020/4/27
*/
private void initBeans() throws Exception {
//获取包下的所有类 TODO
Set<Class<?>> classes = ClassUtil.scanPackage(packageName);
//获取所有的类
ConcurrentHashMap<String, Object> classAnnotation = findClassExistAnnotation(classes);
if (classAnnotation == null || classAnnotation.isEmpty()) {
throw new Exception("该包下没有任何注解");
}
}
/**
* Description: 判断是否有注解，并且初始化到容器里
*
* @param
* @return java.util.concurrent.ConcurrentHashMap<java.lang.String, java.lang.Object>
* @date 9:52 2020/4/27
*/
private ConcurrentHashMap<String, Object> findClassExistAnnotation(Set<Class<?>> classes) throws InstantiationException, IllegalAccessException {
for (Class<?> classinfo : classes) {
SelfService annotation = classinfo.getAnnotation(SelfService.class);
if (annotation != null) {
String className = classinfo.getSimpleName();
String beanId = toLowerCaseFirstOne(className);
Object newInstance = newInstance(classinfo);
beans.put(beanId, newInstance);
}
}
return beans;
}
/**
* Description:首字母转小写
*
* @param s
* @return java.lang.String
* @date 9:57 2020/4/27
*/
private String toLowerCaseFirstOne(String s) {
if(Character.isLowerCase(s.charAt(0))){
return s;
}else {
return (new StringBuilder()).append(Character.toLowerCase(s.charAt(0))).append(s.substring(1)).toString();
}
}
/**
* Description: 根据类名获取实例对象
*
* @param classinfo
* @return java.lang.Object
* @date 9:56 2020/4/27
*/
private Object newInstance(Class<?> classinfo) throws IllegalAccessException, InstantiationException {
return classinfo.newInstance();
}
private void initEntryField() throws Exception {
for (Map.Entry<String, Object> entry : beans.entrySet()) {
//判断属性上是否有注解
Object bean = entry.getValue();
attriAssign(bean);
}
}
/**
* Description: 依赖注入原理
*
* @param object
* @return void
* @date 17:53 2020/4/26
*/
private void attriAssign(Object object) throws Exception {
//1、利用反射获取当前类的属性
Class<? extends Object> classInfo = object.getClass();
Field[] declaredFields = classInfo.getDeclaredFields();
//2、判断当前类属性是否存在注解
for (Field field : declaredFields) {
SelfAutowired extResource = field.getAnnotation(SelfAutowired.class);
if (extResource != null) {
String beanId = field.getName();
Object bean = getBean(beanId);
if (bean != null) {
field.setAccessible(true);
field.set(object, bean);
}
}
}
}
/**
* Description: 根据beanID获取bean
*
* @param beanId
* @return java.lang.Object
* @date 9:41 2020/4/27
*/
public Object getBean(String beanId) throws Exception {
if (StringUtils.isEmpty(beanId)) {
throw new Exception("beanID参数不能为空");
}
Object object = beans.get(beanId);
return object;
}
}
UserService：
public interface UserService {
String getBeanName();
}
UserServiceImpl：
@SelfService
public class UserServiceImpl implements UserService {
@SelfAutowired
Bean bean;
@Override
public String getBeanName() {
return bean.name;
}
}
IocTest：
public class IocTest {
public static void main(String[] args) throws Exception{
SelfPathXmlApplicationContext context = new SelfPathXmlApplicationContext("com.example.ioc");
UserService userService = (UserService) context.getBean("userServiceImpl");
System.out.println(userService.getBeanName());
}
}
标签：substring bsp shm exist users end this targe element
原文地址：https://www.cnblogs.com/ariczky/p/12838646.html
