简版IOC

参考 ：徒手撸框架--实现IoC

核心技术点：

1. 资源解析，如解析定义bean的json文件。 本例用jackson的ObjectMapper解析成List对象。

[
  {
    "name": "computer",
    "className": "com.xiaoyiyiyo.ioc.entity.Computer"
  },
  {
    "name": "cpu",
    "className": "com.xiaoyiyiyo.ioc.entity.Cpu"
  },
  {
    "name": "disk",
    "className": "com.xiaoyiyiyo.ioc.entity.Disk",
    "constructorArgs" : [
      {
      "index" : 0,
      "ref" : "cpu"
      },
      {
        "index" : 1,
        "ref" : "disk"
      }
    ]
  }
]

2. 递归getBean()，利用Java反射生成对象。
   
   

效果：

    public static void main(String[] args) throws Exception {

        JsonApplicationContext applicationContext = new JsonApplicationContext("application.json");
        applicationContext.init();
        Computer computer = (Computer) applicationContext.getBean("computer");
        computer.work();

    }

代码(部分)：

1. 核心基础bean：BeanDefinition，即json资源映射成List.

package com.xiaoyiyiyo.ioc.bean;

import java.util.List;

/**
 * Created by xiaoyiyiyo on 2018/3/6.
 * 映射bean的定义
 */
public class BeanDefinition {
    private String name;

    private String className;

    private String interfaceName;

    private List constructorArgs;

    private List propertyArgs;

    public BeanDefinition() {
    }

    // get/set方法
    ...
}

2. 解析application.json，生成List, 并注册到相应的Map中, 用于后续判断(比如是否已生成对象等等)

List beanDefinitions = JsonUtils.readValue(is, new TypeReference>(){});

if(beanDefinitions != null && !beanDefinitions.isEmpty()) {

     for (BeanDefinition beanDefinition : beanDefinitions) {
         registerBean(beanDefinition.getName(), beanDefinition);
     }
}

3. 递归getBean()， 利用Java发射生成对象

public class BeanFactoryImpl implements BeanFactory {

    private static final ConcurrentHashMap beanMap =
            new ConcurrentHashMap();

    private static final ConcurrentHashMap beanDefineMap =
            new ConcurrentHashMap();

    private static final Set beanNameSet = Collections.synchronizedSet(new HashSet());

    public Object getBean(String name) throws Exception {
        // 是否已生成对象
        Object bean = beanMap.get(name);
        if (bean != null) {
            return bean;
        }

        // 生成bean
        bean = createBean(beanDefineMap.get(name));
        if (bean != null) {
            beanMap.put(name, bean);
        }
        return bean;
    }

    public Object createBean(BeanDefinition beanDefinition) throws Exception {
        String beanName = beanDefinition.getClassName();
        Class clz = ClassUtils.loadClass(beanName);
        if (clz == null) {
            throw new Exception("can not find bean by beanName: " + beanName);
        }
        
        // 此处利用有参构造函数生成并初始化对象了。
        // 看资料感觉spring ioc是先用的无参构造函数生成实例，然后再初始化
        List constructorArgs = beanDefinition.getConstructorArgs();
        List argClazzs = new ArrayList();
        if (constructorArgs != null && !constructorArgs.isEmpty()) {
            List