聊聊自定義SPI如何使用自定義標籤注入到spring容器中

linyb極客之路發表於2021-11-25
Spring

前言

之前我們聊過自定義的SPI如何與spring進行整合，今天我們就來聊下如何通過自定義標籤將spi物件注入到spring容器中

實現套路

1、自定義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： 如果對xsd不熟悉的朋友，可以參考如下連結

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

2、自定義解析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、定義NamespaceHandler實現類處理自定義標籤的處理器

示例：

public class SpiNamespaceHandler extends NamespaceHandlerSupport {

    @Override
    public void init() {
        registerBeanDefinitionParser("scan", new AnnotationBeanDefinitionParser(SpiAnnotationPostProcessor.class));
    }
}
4、將寫入處理器、標籤的位置寫入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目錄底下

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、在啟動類上匯入xml
@SpringBootApplication
@ImportResource(locations = "classpath:/spi.xml")
public class SpiTestXmlApplication {


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


}
3、驗證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));
    }

控制檯輸入如下

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

說明已經匯入到spring容器中

總結

自從spring3+開始引入註解驅動後，在新專案基本上很少會使用xml，但如果是一些老舊的專案，大家如果想實現自定義標籤注入到spring，就可以使用本文的方式。

套路就是如下

  • 　 1、自定義xsd
  • 　　2、自定義解析BeanDefinitionParser解析器
  • 　　3、定義NamespaceHandler實現類處理自定義標籤的處理器
  • 　　4、將寫入處理器、標籤的位置寫入spring.handlers、spring.schemas中

本文的實現也是相對簡單，如果想深入使用，推薦看看dubbo自定義spring標籤

demo連結

https://github.com/lyb-geek/springboot-learning/tree/master/springboot-spi-enhance/springboot-spi-framework-spring

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