前言

之前我们聊过[自定义的SPI如何与spring进行整合]，今天我们就来聊下如何通过自定义标签将spi对象注入到spring容器中

实现套路

1、自定义xsd

示例：

<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
            xmlns:beans="http://www.springframework.org/schema/beans"
            xmlns:tool="http://www.springframework.org/schema/tool"
            xmlns="http://lybgeek.github.com/schema/spi"
            targetNamespace="http://lybgeek.github.com/schema/spi">

    <xsd:import namespace="http://www.w3.org/XML/1998/namespace"/>
    <xsd:import namespace="http://www.springframework.org/schema/beans"
                schemaLocation="http://www.springframework.org/schema/beans/spring-beans.xsd"/>
    <xsd:import namespace="http://www.springframework.org/schema/tool"/>

    <xsd:annotation>
        <xsd:documentation>
            <![CDATA[ Namespace support for spi services ]]></xsd:documentation>
    </xsd:annotation>


    <xsd:complexType name="scanType">
        <xsd:attribute name="id" type="xsd:ID">
            <xsd:annotation>
                <xsd:documentation><![CDATA[ The unique identifier for a bean. ]]></xsd:documentation>
            </xsd:annotation>
        </xsd:attribute>
        <xsd:attribute name="basePackages" type="xsd:string" use="required">
            <xsd:annotation>
                <xsd:documentation><![CDATA[ Specify the spi package name to scan, multiple scan packages are separated by commas ]]></xsd:documentation>
            </xsd:annotation>
        </xsd:attribute>
    </xsd:complexType>

    <xsd:complexType name="interceptorType">
        <xsd:attribute name="id" type="xsd:ID">
            <xsd:annotation>
                <xsd:documentation><![CDATA[ The unique identifier for a bean. ]]></xsd:documentation>
            </xsd:annotation>
        </xsd:attribute>
        <xsd:attribute name="class" type="xsd:string" use="required">
            <xsd:annotation>
                <xsd:documentation><![CDATA[ Interceptor class name]]></xsd:documentation>
            </xsd:annotation>
        </xsd:attribute>
    </xsd:complexType>

    <xsd:complexType name="interceptorChainType">
        <xsd:choice>
            <xsd:element ref="interceptor" minOccurs="1" maxOccurs="unbounded"/>
        </xsd:choice>
    </xsd:complexType>


    <xsd:element name="scan" type="scanType">
        <xsd:annotation>
            <xsd:documentation><![CDATA[ The scan config ]]></xsd:documentation>
        </xsd:annotation>
    </xsd:element>

    <xsd:element name="interceptor" type="interceptorType">
        <xsd:annotation>
            <xsd:documentation><![CDATA[ The interceptor config ]]></xsd:documentation>
        </xsd:annotation>
    </xsd:element>

    <xsd:element name="interceptorChain" type="interceptorChainType">
        <xsd:annotation>
            <xsd:documentation><![CDATA[ The interceptorChainType config ]]></xsd:documentation>
        </xsd:annotation>
    </xsd:element>

</xsd:schema>

ps： 如果对xsd不熟悉的朋友，可以参考如下链接

https://www.w3school.com.cn/schema/index.asp

2、自定义解析BeanDefinitionParser解析器

示例：

public class AnnotationBeanDefinitionParser implements BeanDefinitionParser {

    private final Class<?> beanClass;

    public AnnotationBeanDefinitionParser(Class<?> beanClass) {
        this.beanClass = beanClass;
    }

    @Override
    public BeanDefinition parse(Element element, ParserContext parserContext) {

        String packageToScan = element.getAttribute("basePackages");
        String[] packagesToScan = trimArrayElements(commaDelimitedListToStringArray(packageToScan));

        RootBeanDefinition beanDefinition = new RootBeanDefinition();
        beanDefinition.setBeanClass(beanClass);
        beanDefinition.setLazyInit(false);
        beanDefinition.getConstructorArgumentValues().addIndexedArgumentValue(0,packagesToScan);
        String beanName = BeanUtils.generateBeanName(element,"id",parserContext,beanClass.getName());
        parserContext.getRegistry().registerBeanDefinition(beanName,beanDefinition);

        return beanDefinition;
    }


}

3、定义NamespaceHandler实现类处理自定义标签的处理器

示例：

public class SpiNamespaceHandler extends NamespaceHandlerSupport {

    @Override
    public void init() {
        registerBeanDefinitionParser("scan", new AnnotationBeanDefinitionParser(SpiAnnotationPostProcessor.class));
    }
}

4、将写入处理器、标签的位置写入spring.handlers、spring.schemas中

示例：

spring.handlers

http\://lybgeek.github.com/schema/spi=com.github.lybgeek.spring.schema.SpiNamespaceHandler

spring.schemas

http\://lybgeek.github.com/schema/spi/spi.xsd=META-INF/spi/spi.xsd

注： spring.handlers、spring.schemas需放置在resource/META-INF目录底下

示例演示

1、配置xml

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:spi="http://lybgeek.github.com/schema/spi"
       xmlns="http://www.springframework.org/schema/beans"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.3.xsd
       http://lybgeek.github.com/schema/spi http://lybgeek.github.com/schema/spi/spi.xsd">

    <spi:scan basePackages="com.github.lybgeek"></spi:scan>

2、在启动类上导入xml

@SpringBootApplication
@ImportResource(locations = "classpath:/spi.xml")
public class SpiTestXmlApplication {


    public static void main(String[] args) throws Exception{
        SpringApplication.run(SpiTestXmlApplication.class);
    }


}

3、验证SPI是否注入spring容器

 @Override
    public void run(ApplicationArguments args) throws Exception {

        applicationContext.getBeansOfType(SpringSqlDialect.class)
                .forEach((beanName,bean) -> System.out.println(beanName + "-->" + bean));
    }

控制台输入如下

springMysqlDialect-->com.github.lybgeek.dialect.mysql.SpringMysqlDialect@73041b7d
mysql-hello-->com.github.lybgeek.dialect.mysql.SpringMysqlDialect@574059d5
springOracleDialect-->com.github.lybgeek.dialect.oracle.SpringOracleDialect@4a50d04a

说明已经导入到spring容器中

总结

自从spring3+开始引入注解驱动后，在新项目基本上很少会使用xml，但如果是一些老旧的项目，大家如果想实现自定义标签注入到spring，就可以使用本文的方式。

套路就是如下

• 1、自定义xsd
• 2、自定义解析BeanDefinitionParser解析器
• 3、定义NamespaceHandler实现类处理自定义标签的处理器
• 4、将写入处理器、标签的位置写入spring.handlers、spring.schemas中

本文的实现也是相对简单，如果想深入使用，推荐看看dubbo自定义spring标签