手写一个简单的spring IOC容器

加载解析配置bean文件

利用反射实例化bean

通过工厂模式获取实例

 用map表示容器

一、加载xml配置文件

public class XmlConfig {
    
    public static Map getConfig(String path){
        Map config = new HashMap();
        // 1、读取applicationContext
        InputStream inputStream = XmlConfig.class.getResourceAsStream(path);
        SAXReader reader = new SAXReader();
        document read = null;
        try {
            read = reader.read(inputStream);
        } catch (documentException e) {
            e.printStackTrace();
            throw new RuntimeException("配置文件错误，请检查");
        }
        Element rootElement = read.getRootElement();
        List elements = rootElement.elements("bean");
        if (elements == null){
            return config;
        }
        for (Element element : elements) {
            Bean bean = new Bean();
            // 获取bean的id和class
            String id = element.attributevalue("id");
            String className = element.attributevalue("class");
            bean.setId(id);
            bean.setClassName(className);

            List properties = element.elements("property");
            List pros = new ArrayList();
            if (properties != null){
                for (Element property : properties) {
                    Property pro = new Property();
                    // 加载参数
                    String name = property.attributevalue("name");
                    String value = property.attributevalue("value");
                    String ref = property.attributevalue("ref");
                    pro.setName(name);
                    pro.setValue(value);
                    pro.setRef(ref);
                    bean.getProperties().add(pro);
                }
            }

            // 校验id不重复
            if (config.containsKey(id)){
                throw new RuntimeException("bean节点ID重复：" + id);
            }
            config.put(id, bean);
        }
        return config;
    }
}

 二、实例化bean

public class ClassPathXmlApplicationContext implements BeanFactory {
    private Map ioc;
    private Map config;
    
    public ClassPathXmlApplicationContext(String path){
        this.ioc = new HashMap();
        this.config = XmlConfig.getConfig(path);
        for (Map.Entry entry : this.config.entrySet()) {
            String key = entry.getKey();
            Bean bean = entry.getValue();
            Object value = createBean(bean);
            this.ioc.put(key, value);
        }
    }

    
    public Object createBean(Bean bean){
        // 利用反射，获取bean实例
        Class clazz = null;
        try {
            clazz = Class.forName(bean.getClassName());
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException("配置的class不合理");
        }
        Object instance = null;
        try {
            instance = clazz.newInstance();
        } catch (Exception e) {
            e.printStackTrace();
            throw new RuntimeException("创建bean实例失败");
        }
        List properties = bean.getProperties();
        if (properties == null){
            return instance;
        }
        for (Property property : properties) {
            String name = property.getName();
            String value = property.getValue();
            String ref = property.getRef();
            if(value != null){
                Field field = null;
                try {
                    field = clazz.getDeclaredField(name);
                    field.setAccessible(true);
                    field.set(instance, value);
                } catch (Exception e) {
                    e.printStackTrace();
                    throw new RuntimeException("属性名称不合法");
                }
            }
            if(ref != null){
                try{
                    Field field = clazz.getDeclaredField(name);
                    field.setAccessible(true);
                    Object obj = ioc.get(ref);
                    field.set(instance, obj);
                }catch (Exception e){
                    e.printStackTrace();
                    throw new RuntimeException("没有找到依赖的对象");
                }
            }
        }
        return instance;
    }

    public Object getBean(String id){
        return this.ioc.get(id);
    }

}

三、工厂模式获取实例

public interface BeanFactory {
    Object getBean(String beanName);
}

四、测试类

public class AppTest {

    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("/AppContext.xml");

        User fundUser = (User)context.getBean("user");
        System.out.println(fundUser.toString());
    }
}

五、其它类

// Bean
public class Bean {
    private String id;
    private String className;
    private List properties = new ArrayList();

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getClassName() {
        return className;
    }

    public void setClassName(String className) {
        this.className = className;
    }

    public List getProperties() {
        return properties;
    }
}

// Property
public class Property {
    private String name;
    private String value;
    private String ref;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }

    public String getRef() {
        return ref;
    }

    public void setRef(String ref) {
        this.ref = ref;
    }
}