關于對Java List的通用排序實現

jopen 13年前發布 | 42K 次閱讀 Java Java開發

List的排序大家都會想到實現Comparator接口，但是如果我們需要對list排序是動態，就比較崩潰了，復雜度不言而喻。經過仔細思索，寫了一個工具類，使用反射機制實現對list對象的排序功能，專門用于List對象的排序工作。

package xzknet.net.csdn.blog.utils;
import java.beans.PropertyDescriptor;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import org.springframework.beans.BeanUtils;
/**

List排序工具

@author Ken.xu(mailto:xzknet@gmail.com)
@version 1.0 Copyright 2012-9-18 下午04:37:17
@param <T>
*/
public class ListSortUtil<T> {
 private Map<Method, Direction> sortField = new LinkedHashMap<Method, Direction>();
 private Map<String, Method> propertyMethodMap = null;
// Method[] methods
 public ListSortUtil(final Class clazz) {

 PropertyDescriptor[] propertyDescriptor = BeanUtils.getPropertyDescriptors(clazz);
 Map<String, Method> propertyMethodMap = new HashMap<String, Method>();
 for (PropertyDescriptor pd : propertyDescriptor) {
     String key = pd.getName();
     Method value = pd.getReadMethod();
     propertyMethodMap.put(key, value);
 }
 this.propertyMethodMap = propertyMethodMap;

}
public void clear() {

 sortField.clear();

}
/**

增加一個降序

@param fieldName
@throws NoSuchMethodException
@author Ken_xu
*/
public void addDesc(String fieldName) throws NoSuchMethodException {
 addFieldMethod(fieldName, Direction.DESC);
}
/**

增加一個升序

@param fieldName
@throws NoSuchMethodException
@author Ken_xu
*/
public void addAsc(String fieldName) throws NoSuchMethodException {
 addFieldMethod(fieldName, Direction.ASC);
}
/**

增加一個字段排序模式

@param fieldName
@param direction
@throws NoSuchMethodException
@author Ken_xu
*/
private void addFieldMethod(String fieldName, Direction direction) throws NoSuchMethodException {
 Method method = propertyMethodMap.get(fieldName);
 if (method == null) {

 throw new NoSuchMethodException(fieldName);

} else {

 sortField.put(method, direction);

}
}
public List<T> sortList(List<T> list) {
 if (sortField.isEmpty() == false) {

 Comparator<T> comparator = new Comparator<T>() {
     public int compare(T o1, T o2) {
         int flag = 0;
         for (Map.Entry<Method, Direction> entry : sortField.entrySet()) {
             Method method = entry.getKey();
             Direction direction = entry.getValue();
             if (direction == Direction.ASC) {
                 // DESC:降序
                 flag = this.compareByFlag(method, o1, o2);
             } else {
                 // ASC:升序
                 flag = this.compareByFlag(method, o2, o1);
             }
             if (flag != 0) {
                 break;
             }
         }
         if (flag > 0) {
             flag = 1;
         } else if (flag < 0) {
             flag = -1;
         }
         return flag;
     }

     /**
      * 如果t1大于t2:1<br>
      * t1等于t2:0<br>
      * t1小于t2:-1
      * 
      * @param flag
      * @param t1
      * @param t2
      * @return
      * @author Ken_xu
      */
     private int compareByFlag(Method method, T t1, T t2) {
         int flag = 0;
         try {
             String methodReturn1 = method.invoke(t1).toString();
             String methodReturn2 = method.invoke(t2).toString();
             flag = methodReturn1.compareTo(methodReturn2);
         } catch (IllegalArgumentException e) {
             e.printStackTrace();
         } catch (IllegalAccessException e) {
             e.printStackTrace();
         } catch (InvocationTargetException e) {
             e.printStackTrace();
         }
         return flag;
     }

 };
 Collections.sort(list, comparator);

}
 return list;
}
/**

排序方式：
<p>
ASC:升序<br/> DESC:降序
*/
enum Direction {
 ASC, DESC
};
}</pre>測試用例也給大家提供一個package xzknet.net.csdn.blog.utils;



import java.util.ArrayList;
import java.util.List;
import junit.framework.TestCase;
public class ListSortUtilTest extends TestCase {

private List<TestUser> list = null;

/**
 * 打印清單
 * 
 * @author Ken_xu
 */
private void printListEg() {
    List<TestUser> TestUserList = new ArrayList<TestUser>();
    for (int i = 0, maxIdx = list.size(); i < maxIdx; i++) {
        TestUser tm = list.get(i);
        String showTxt = String.format("%d)\t modelName=%s;\t\t extendsModel=%s;", i, tm.getModelName(), tm.getExtendsModels());
        System.out.println(showTxt);
        if (i == (maxIdx - 1)) {
            showTxt = String.format("...................總共：%d條", list.size());
            System.out.println(showTxt);
        }
        TestUserList.add(tm);
    }
    list = TestUserList;
}

/**
 * 初始化測試用例
 */
protected void setUp() throws Exception {
    super.setUp();

    List<TestUser> TestUserList = new ArrayList<TestUser>();
    long rowNum = 0l;
    for (int i = 0; i < 10; i++) {
        TestUser tm = new TestUser();
        if (i % 2 == 0) {
            // 每兩個對象的modelName相同
            rowNum = Math.round(Math.random() * 100);
        }
        tm.setModelName("AAA_TEST_" + rowNum);
        tm.setExtendsModels("BBBBBBB" + i);
        TestUserList.add(tm);
    }
    list = TestUserList;
}

/**
 * 測試排序
 * 
 * @author Ken_xu
 */
public void testSort() {
    ListSortUtil<TestUser> sortUtil = new ListSortUtil(TestUser.class);
    try {
        sortUtil.addDesc("modelName");
        sortUtil.addAsc("extendsModels");
    } catch (NoSuchMethodException e) {
        e.printStackTrace();
    }
    System.out.println("打印排序前結果");
    printListEg();
    sortUtil.sortList(list);
    System.out.println("打印排序后結果");
    printListEg();
}

class TestUser {
    String modelName, extendsModels;

    public String getModelName() {
        return modelName;
    }

    public void setModelName(String modelName) {
        this.modelName = modelName;
    }

    public String getExtendsModels() {
        return extendsModels;
    }

    public void setExtendsModels(String extendsModels) {
        this.extendsModels = extendsModels;
    }
}

}</pre>測試結果如下：
打印排序前結果
0)   modelName=AAA_TEST_48;      extendsModel=BBBBBBB0;
1)   modelName=AAA_TEST_48;      extendsModel=BBBBBBB1;
2)   modelName=AAA_TEST_29;      extendsModel=BBBBBBB2;
3)   modelName=AAA_TEST_29;      extendsModel=BBBBBBB3;
4)   modelName=AAA_TEST_1;       extendsModel=BBBBBBB4;
5)   modelName=AAA_TEST_1;       extendsModel=BBBBBBB5;
6)   modelName=AAA_TEST_63;      extendsModel=BBBBBBB6;
7)   modelName=AAA_TEST_63;      extendsModel=BBBBBBB7;
8)   modelName=AAA_TEST_73;      extendsModel=BBBBBBB8;
9)   modelName=AAA_TEST_73;      extendsModel=BBBBBBB9;
...................總共：10條
打印排序后結果
0)   modelName=AAA_TEST_73;      extendsModel=BBBBBBB8;
1)   modelName=AAA_TEST_73;      extendsModel=BBBBBBB9;
2)   modelName=AAA_TEST_63;      extendsModel=BBBBBBB6;
3)   modelName=AAA_TEST_63;      extendsModel=BBBBBBB7;
4)   modelName=AAA_TEST_48;      extendsModel=BBBBBBB0;
5)   modelName=AAA_TEST_48;      extendsModel=BBBBBBB1;
6)   modelName=AAA_TEST_29;      extendsModel=BBBBBBB2;
7)   modelName=AAA_TEST_29;      extendsModel=BBBBBBB3;
8)   modelName=AAA_TEST_1;       extendsModel=BBBBBBB4;
9)   modelName=AAA_TEST_1;       extendsModel=BBBBBBB5;
...................總共：10條
來自：http://blog.csdn.net/xzknet/article/details/7992403

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