SpringBoot MapperScan添加动态配置(占位符)

参考文章：https://www.jianshu.com/p/a0a317fd8c67

在对Mybatis自动扫描配置中，使用注解配置时，@MapperScan中的配置，通常配置如下：

@MapperScan(basePackages = {"com.aa.**.mapper","com.bb.**.mapper"}, sqlSessionFactoryRef = "sqlSessionFactory")

不支持在yml或properties文件中动态配置。因为MapperScan注解功能的实现类MapperScannerRegistrar实现的是ImportBeanDefinitionRegistrar。在对@Configuration注解标记的类配置时，实现占位符功能的PropertyPlaceholderAutoConfiguration还没有开始加载。

MapperScannerRegistrard的核心代码如下：

List basePackages = new ArrayList();
        basePackages.addAll((Collection)Arrays.stream(annoAttrs.getStringArray("value")).filter(StringUtils::hasText).collect(Collectors.toList()));
        basePackages.addAll((Collection)Arrays.stream(annoAttrs.getStringArray("basePackages")).filter(StringUtils::hasText).collect(Collectors.toList()));
        basePackages.addAll((Collection)Arrays.stream(annoAttrs.getClassArray("basePackageClasses")).map(ClassUtils::getPackageName).collect(Collectors.toList()));
        scanner.registerFilters();
        scanner.doScan(StringUtils.toStringArray(basePackages));

从上图代码中可以看出，为了拓展支持占位符动态配置，只需把basePackages的加载改写即可。

1、参考MapperScannerRegistrard，实现 ImportBeanDefinitionRegistrar和ResourceLoaderAware两个接口

2、为了动态读取配置文件信息，需要引入Environment，所以实现EnvironmentAware接口

3、代码

MapperScannerRegistrar.java

import org.mybatis.spring.mapper.ClassPathMapperScanner;
import org.mybatis.spring.mapper.MapperFactoryBean;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.BeanUtils;
import org.springframework.beans.factory.support.BeanDefinitionRegistry;
import org.springframework.beans.factory.support.BeanNameGenerator;
import org.springframework.context.EnvironmentAware;
import org.springframework.context.ResourceLoaderAware;
import org.springframework.context.annotation.ImportBeanDefinitionRegistrar;
import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
import org.springframework.core.annotation.AnnotationAttributes;
import org.springframework.core.env.Environment;
import org.springframework.core.io.ResourceLoader;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.util.ClassUtils;
import org.springframework.util.StringUtils;

import java.lang.annotation.Annotation;
import java.util.*;
import java.util.stream.Collectors;

public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware,EnvironmentAware {

    private Environment environment;

    private ResourceLoader resourceLoader;

    private  static  final Logger logger = LoggerFactory.getLogger(MapperScannerRegistrar. class);

    @Override
    public void setEnvironment(Environment environment) {
        this.environment = environment;
    }

    @Override
    public void setResourceLoader(ResourceLoader resourceLoader) {
        this.resourceLoader = resourceLoader;
    }

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {

        AnnotationAttributes mapperScanAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScanner.class.getName()));
        if (mapperScanAttrs != null) {
            this.registerBeanDefinitions(mapperScanAttrs, registry);
        }
    }

    void registerBeanDefinitions(AnnotationAttributes annoAttrs, BeanDefinitionRegistry registry) {
        ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
        Optional var10000 = Optional.ofNullable(this.resourceLoader);
        Objects.requireNonNull(scanner);
        Class annotationClass = annoAttrs.getClass("annotationClass");
        if (!Annotation.class.equals(annotationClass)) {
            scanner.setAnnotationClass(annotationClass);
        }

        Class markerInterface = annoAttrs.getClass("markerInterface");
        if (!Class.class.equals(markerInterface)) {
            scanner.setMarkerInterface(markerInterface);
        }

        Class generatorClass = annoAttrs.getClass("nameGenerator");
        if (!BeanNameGenerator.class.equals(generatorClass)) {
            scanner.setBeanNameGenerator((BeanNameGenerator) BeanUtils.instantiateClass(generatorClass));
        }

        Class mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");
        if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {
            scanner.setMapperFactoryBeanClass(mapperFactoryBeanClass);
        }

        scanner.setSqlSessionTemplateBeanName(annoAttrs.getString("sqlSessionTemplateRef"));
        scanner.setSqlSessionFactoryBeanName(annoAttrs.getString("sqlSessionFactoryRef"));
        List basePackages = new ArrayList();
        basePackages.addAll(Arrays.stream(annoAttrs.getStringArray("value")).filter(StringUtils::hasText).collect(Collectors.toList()));
        for (String pkg : annoAttrs.getStringArray("basePackages")) {
            if (StringUtils.hasText(pkg)) {
                String value = parsePlaceHolder(pkg);
                if(StringUtils.hasText(value)){
                    List valueList = Arrays.asList(value.split(","));
                    for(String base : valueList){
                        basePackages.add(base);
                    }
                }
            }
        }
        basePackages.addAll(Arrays.stream(annoAttrs.getClassArray("basePackageClasses")).map(ClassUtils::getPackageName).collect(Collectors.toList()));
        scanner.registerFilters();
        scanner.doScan(StringUtils.toStringArray(basePackages));
    }

    private String parsePlaceHolder(String pro) {
        if (StringUtils.hasText(pro) && pro.contains(PropertySourcesPlaceholderConfigurer.DEFAULT_PLACEHOLDER_PREFIX)) {
            String value = environment.getProperty(pro.substring(2, pro.length() - 1));

            if (logger.isDebugEnabled()) {
                logger.debug("find placeholder value " + value + " for key " + pro);
            }

            if (null == value) {
                throw new IllegalArgumentException("property " + pro + " can not find!!!");
            }
            return value;
        }
        return pro;
    }
}

MapperScanner.java

import org.mybatis.spring.mapper.MapperFactoryBean;
import org.springframework.beans.factory.support.BeanNameGenerator;
import org.springframework.context.annotation.Import;

import java.lang.annotation.*;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
@Documented
@Import({MapperScannerRegistrar.class})
public @interface MapperScanner {
    String[] value() default {};

    String[] basePackages() default {};

    Class[] basePackageClasses() default {};

    Class nameGenerator() default BeanNameGenerator.class;

    Class annotationClass() default Annotation.class;

    Class markerInterface() default Class.class;

    String sqlSessionTemplateRef() default "";

    String sqlSessionFactoryRef() default "";

    Class factoryBean() default MapperFactoryBean.class;
}

4、使用MapperScanner，占位符扫描配置

@MapperScanner(basePackages = { "${mybatis.mapperScanner.basePackage}" }, sqlSessionFactoryRef = "sqlSessionFactory")

mybatis:
  mapperScanner:
    basePackage: com.aa.**.mapper,com.bb.**.mapper