Mybatis ResolverUtil的设计概念

设计模式原则之开放-封闭原则

　　程序扩展对外开放，修改对外封闭

ResolverUtil

其中有一个接口、两个内部类，Class对象和Annotation对象被封装成了Test对象

Test

Mybatis ResolverUtil的设计概念

两个实现类，核心功能是匹配Class类型

Mybatis ResolverUtil的设计概念

IsA

public static class IsA implements Test {
    private Class<?> parent;

    /** Constructs an IsA test using the supplied Class as the parent class/interface. */
    public IsA(Class<?> parentType) {
      this.parent = parentType;
    }

    /** Returns true if type is assignable to the parent type supplied in the constructor. */
    @Override
    public boolean matches(Class<?> type) {
      return type != null && parent.isAssignableFrom(type);
    }

    @Override
    public String toString() {
      return "is assignable to " + parent.getSimpleName();
    }
}

AnnotatedWith

public static class AnnotatedWith implements Test {
    private Class<? extends Annotation> annotation;

    /** Constructs an AnnotatedWith test for the specified annotation type. */
    public AnnotatedWith(Class<? extends Annotation> annotation) {
      this.annotation = annotation;
    }

    /** Returns true if the type is annotated with the class provided to the constructor. */
    @Override
    public boolean matches(Class<?> type) {
      return type != null && type.isAnnotationPresent(annotation);
    }

    @Override
    public String toString() {
      return "annotated with @" + annotation.getSimpleName();
    }
}

使用

String packageName = "com/wjz/mybatis/type/scan";
ResolverUtil<Class<?>> resolverUtil = new ResolverUtil<Class<?>>();
resolverUtil.find(new ResolverUtil.IsA(CommonService.class), packageName);
Set<Class<? extends Class<?>>> handlerSet = resolverUtil.getClasses();

如此设计

我们可以实现Test接口，传参find方法时传入，而不用修改ResolverUtil的内部方法。

package com.wjz.mybatis.type.scan;

import org.apache.ibatis.io.ResolverUtil.Test;

public class Testtest implements Test {

    @Override
    public boolean matches(Class<?> type) {
        if (type == Testtest.class) {
            return true;
        }
        return false;
    }

}