dubbo-common/src/main/java/com/alibaba/dubbo/common/extension/support/ActivateComparator.java

/*
 * Copyright 1999-2012 Alibaba Group.
 *  
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *  
 *      http://www.apache.org/licenses/LICENSE-2.0
 *  
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.alibaba.dubbo.common.extension.support;

import java.util.Comparator;

import com.alibaba.dubbo.common.extension.Activate;
import com.alibaba.dubbo.common.extension.ExtensionLoader;
import com.alibaba.dubbo.common.extension.SPI;

/**
 * OrderComparetor
 * 
 * @author william.liangf
 */
public class ActivateComparator implements Comparator<Object> {
    
    public static final Comparator<Object> COMPARATOR = new ActivateComparator();

    public int compare(Object o1, Object o2) {
        if (o1 == null && o2 == null) {
            return 0;
        }
        if (o1 == null) {
            return -1;
        }
        if (o2 == null) {
            return 1;
        }
        if (o1.equals(o2)) {
            return 0;
        }
        Activate a1 = o1.getClass().getAnnotation(Activate.class);
        Activate a2 = o2.getClass().getAnnotation(Activate.class);
        if ((a1.before().length > 0 || a1.after().length > 0  
                || a2.before().length > 0 || a2.after().length > 0) 
                && o1.getClass().getInterfaces().length > 0
                && o1.getClass().getInterfaces()[0].isAnnotationPresent(SPI.class)) {
            ExtensionLoader<?> extensionLoader = ExtensionLoader.getExtensionLoader(o1.getClass().getInterfaces()[0]);
            if (a1.before().length > 0 || a1.after().length > 0) {
                String n2 = extensionLoader.getExtensionName(o2.getClass());
                for (String before : a1.before()) {
                    if (before.equals(n2)) {
                        return -1;
                    }
                }
                for (String after : a1.after()) {
                    if (after.equals(n2)) {
                        return 1;
                    }
                }
            }
            if (a2.before().length > 0 || a2.after().length > 0) {
                String n1 = extensionLoader.getExtensionName(o1.getClass());
                for (String before : a2.before()) {
                    if (before.equals(n1)) {
                        return 1;
                    }
                }
                for (String after : a2.after()) {
                    if (after.equals(n1)) {
                        return -1;
                    }
                }
            }
        }
        int n1 = a1 == null ? 0 : a1.order();
        int n2 = a2 == null ? 0 : a2.order();
        return n1 > n2 ? 1 : -1; // 就算n1 == n2也不能返回0，否则在HashSet等集合中，会被认为是同一值而覆盖
    }

}