spring源码学习一

个人的学习总结如下：

1.系统环境变量验证，判断环境是否包含某个变量，如果没有，则启动不了

继承ClassPathXmlApplicationContext，重写initPropertySources方法（由于AbstractApplicationContext的refresh方法中，prepareRefresh中initPropertySources为空，方便后续扩展）

public class MyClassPathXmlApplicationContent extends ClassPathXmlApplicationContext {

    public MyClassPathXmlApplicationContent(String configLocations) {
        super(configLocations);
    }

    @Override
    protected void initPropertySources() {
        System.out.println(this.getEnvironment().getRequiredProperty("abc"));
    }
}

2.自定义标签

自定义handler，handler找到parser，parser填充实体

自定义一个实体类

ublic class Jsuper {

    private String id;
    private String username;
    private Integer height;
    private Integer age;

    public String getId() {
        return id;
    }

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

    public String getUsername() {
        return username;
    }

    public void setUsername(String username) {
        this.username = username;
    }

    public Integer getHeight() {
        return height;
    }

    public void setHeight(Integer height) {
        this.height = height;
    }

    public Integer getAge() {
        return age;
    }

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

　　自定义parser，继承AbstractSingleBeanDefinitionParser,重写getBeanClass，重写doParse方法

public class JsuperBeanDefinitionParser extends AbstractSingleBeanDefinitionParser {

    @Override
    protected Class<?> getBeanClass(Element element) {
        return Jsuper.class;
    }

    @Override
    protected void doParse(Element element, BeanDefinitionBuilder builder) {

        if(element.hasAttribute("id")){
            builder.addPropertyValue("id",element.getAttribute("id"));
        }

        if(element.hasAttribute("username")){
            builder.addPropertyValue("username",element.getAttribute("username"));
        }
        if(element.hasAttribute("height")){
            builder.addPropertyValue("height",element.getAttribute("height"));
        }
        if(element.hasAttribute("age")){
            builder.addPropertyValue("age",element.getAttribute("age"));
        }
    }
}

　　自定义handler，继承NameSpaceHandlerSupport,重写init方法

public class JsuperNamespaceHandler extends NamespaceHandlerSupport {
    @Override
    public void init() {
        registerBeanDefinitionParser("user",new JsuperBeanDefinitionParser());
    }
}

　　resources下新增spring.handlers,spring.schemas

spring.handlers
http\://www.jsuper.com/schema/user=com.jsuper.test.custombean.JsuperNamespaceHandler
spring.schemas
http\://www.jsuper.com/schema/user.xsd=META-INF/user.xsd

　　新增user.xsd

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema"
        targetNamespace="http://www.jsuper.com/schema/user"
        xmlns:tns="http://www.jsuper.com/schema/user"
        elementFormDefault="qualified">
    <element name="user">
        <complexType>
            <attribute name="id" type="string"></attribute>
            <attribute name="username" type="string"></attribute>
            <attribute name="height" type="integer"></attribute>
            <attribute name="age" type="integer"></attribute>
        </complexType>
    </element>
</schema>

　　在xml中新增

xmlns:jsuper="http://www.jsuper.com/schema/user"
http://www.jsuper.com/schema/user http://www.jsuper.com/schema/user.xsd
<jsuper:user id="aaa"  username="zs" age="18" height="180"></jsuper:user>

可以从BeanFactory中获取aaa，这里有一个需要注意的，xml中的bean必须有id