吃透Spring源码（三）：自定义配置文件标签

> Spring的强大之处不仅仅在于它为Java开发者提供了极大便利，更在于它的开放式架构，使得用户可以拥有最大扩展Spring的能力。

我们在用xml定义spring信息时，默认的element只包含beans，bean，import，alias这四个，其它任何标签都属于自定义标签，均需要引入相应的命名空间，如：context，aop标签等。

protected void parseBeanDefinitions(Element root, BeanDefinitionParserDelegate delegate) {
   
     
		if (delegate.isDefaultNamespace(root)) {
   
     
			NodeList nl = root.getChildNodes();
			for (int i = 0; i < nl.getLength(); i++) {
   
     
				Node node = nl.item(i);
				if (node instanceof Element) {
   
     
					Element ele = (Element) node;
					if (delegate.isDefaultNamespace(ele)) {
   
     
						//处理默认的标签元素
						parseDefaultElement(ele, delegate);
					}
					else {
   
     
						//处理自定义的标签元素
						delegate.parseCustomElement(ele);
					}
				}
			}
		}
		else {
   
     
			delegate.parseCustomElement(root);
		}
	}

对应的源码处理在DefaultBeanDefinitionDocumentReader类的parseBeanDefinitions方法里面。

自定义标签元素

1，定义People.java

public class People {
   
     
    private String id;
    private int age;
    private String name;
    private String address;

    public People(String id, int age, String name, String address) {
   
     
        this.id = id;
        this.age = age;
        this.name = name;
        this.address = address;
    }

    public People() {
   
     
    }

    public String getId() {
   
     
        return id;
    }

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

    public int getAge() {
   
     
        return age;
    }

    public void setAge(int age) {
   
     
        this.age = age;
    }

    public String getName() {
   
     
        return name;
    }

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

    public String getAddress() {
   
     
        return address;
    }

    public void setAddress(String address) {
   
     
        this.address = address;
    }

    @Override
    public String toString() {
   
     
        return "People{" +
                "id='" + id + '\'' +
                ", age=" + age +
                ", name='" + name + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}