JAVA 集合 List 分组的两种方法
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JAVA 集合 List 分组的两种方法
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<span class="link_postdate">2016-05-25 19:25</span>
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从网上找了两种方法,效率差不多,这里贴出代码供大家参考
实体类Data
- public class Data {
- private Long id ;
- private Long courseId ;
- private String content ;
- public Long getId() {
- return id;
- }
- public Data setId(Long id) {
- this.id = id;
- return this ;
- }
- public Long getCourseId() {
- return courseId;
- }
- public Data setCourseId(Long courseId) {
- this.courseId = courseId;
- return this ;
- }
- public String getContent() {
- return content;
- }
- public Data setContent(String content) {
- this.content = content;
- return this ;
- }
- }

public class Data {
private Long id ;
private Long courseId ;
private String content ;
public Long getId() {
return id;
}
public Data setId(Long id) {
this.id = id;
return this ;
}
public Long getCourseId() {
return courseId;
}
public Data setCourseId(Long courseId) {
this.courseId = courseId;
return this ;
}
public String getContent() {
return content;
}
public Data setContent(String content) {
this.content = content;
return this ;
}
}
排序类
- <pre name="code" class="java">import java.lang.reflect.Method;
- import java.util.ArrayList;
- import java.util.Collection;
- import java.util.HashMap;
- import java.util.Iterator;
- import java.util.List;
- import java.util.Map;
- import com.framework.util.ParamUtils;
- public class CommonUtils {
- /**
- * 分組依據接口,用于集合分組時,獲取分組依據
- *
- * @author ZhangLiKun
- * @title GroupBy
- * @date 2013-4-23
- */
- public interface GroupBy<T> {
- T groupby(Object obj);
- }
- /**
- *
- * @param colls
- * @param gb
- * @return
- */
- public static final <T extends Comparable<T>, D> Map<T, List<D>> group(Collection<D> colls, GroupBy<T> gb) {
- if (colls == null || colls.isEmpty()) {
- System.out.println("分組集合不能為空!");
- return null;
- }
- if (gb == null) {
- System.out.println("分組依據接口不能為Null!");
- return null;
- }
- Iterator<D> iter = colls.iterator();
- Map<T, List<D>> map = new HashMap<T, List<D>>();
- while (iter.hasNext()) {
- D d = iter.next();
- T t = gb.groupby(d);
- if (map.containsKey(t)) {
- map.get(t).add(d);
- } else {
- List<D> list = new ArrayList<D>();
- list.add(d);
- map.put(t, list);
- }
- }
- return map;
- }
- /**
- * 将List<V>按照V的methodName方法返回值(返回值必须为K类型)分组,合入到Map<K, List<V>>中<br>
- * 要保证入参的method必须为V的某一个有返回值的方法,并且该返回值必须为K类型
- *
- * @param list
- * 待分组的列表
- * @param map
- * 存放分组后的map
- * @param clazz
- * 泛型V的类型
- * @param methodName
- * 方法名
- */
- public static <K, V> void listGroup2Map(List<V> list, Map<K, List<V>> map, Class<V> clazz, String methodName) {
- // 入参非法行校验
- if (null == list || null == map || null == clazz || !ParamUtils.chkString(methodName)) {
- System.out.print("CommonUtils.listGroup2Map 入参错误,list:" + list + " ;map:" + map + " ;clazz:" + clazz + " ;methodName:" + methodName);
- return;
- }
- // 获取方法
- Method method = getMethodByName(clazz, methodName);
- // 非空判断
- if (null == method) {
- return;
- }
- // 正式分组
- listGroup2Map(list, map, method);
- }
- /**
- * 根据类和方法名,获取方法对象
- *
- * @param clazz
- * @param methodName
- * @return
- */
- public static Method getMethodByName(Class<?> clazz, String methodName) {
- Method method = null;
- // 入参不能为空
- if (null == clazz || !ParamUtils.chkString(methodName)) {
- System.out.print("CommonUtils.getMethodByName 入参错误,clazz:" + clazz + " ;methodName:" + methodName);
- return method;
- }
- try {
- method = clazz.getDeclaredMethod(methodName);
- } catch (Exception e) {
- System.out.print("类获取方法失败!");
- }
- return method;
- }
- /**
- * 将List<V>按照V的某个方法返回值(返回值必须为K类型)分组,合入到Map<K, List<V>>中<br>
- * 要保证入参的method必须为V的某一个有返回值的方法,并且该返回值必须为K类型
- *
- * @param list
- * 待分组的列表
- * @param map
- * 存放分组后的map
- * @param method
- * 方法
- */
- @SuppressWarnings("unchecked")
- public static <K, V> void listGroup2Map(List<V> list, Map<K, List<V>> map, Method method) {
- // 入参非法行校验
- if (null == list || null == map || null == method) {
- System.out.print("CommonUtils.listGroup2Map 入参错误,list:" + list + " ;map:" + map + " ;method:" + method);
- return;
- }
- try {
- // 开始分组
- Object key;
- List<V> listTmp;
- for (V val : list) {
- key = method.invoke(val);
- listTmp = map.get(key);
- if (null == listTmp) {
- listTmp = new ArrayList<V>();
- map.put((K) key, listTmp);
- }
- listTmp.add(val);
- }
- } catch (Exception e) {
- System.out.print("分组失败!");
- }
- }
- }

<pre name="code" class="java">import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map; import com.framework.util.ParamUtils; public class CommonUtils {/**
* 分組依據接口,用于集合分組時,獲取分組依據
*
* @author ZhangLiKun
* @title GroupBy
* @date 2013-4-23
*/
public interface GroupBy<T> {
T groupby(Object obj);
} /**
*
* @param colls
* @param gb
* @return
*/
public static final <T extends Comparable<T>, D> Map<T, List<D>> group(Collection<D> colls, GroupBy<T> gb) {
if (colls == null || colls.isEmpty()) {
System.out.println("分組集合不能為空!");
return null;
}
if (gb == null) {
System.out.println("分組依據接口不能為Null!");
return null;
}
Iterator<D> iter = colls.iterator();
Map<T, List<D>> map = new HashMap<T, List<D>>();
while (iter.hasNext()) {
D d = iter.next();
T t = gb.groupby(d);
if (map.containsKey(t)) {
map.get(t).add(d);
} else {
List<D> list = new ArrayList<D>();
list.add(d);
map.put(t, list);
}
}
return map;
}
/**
* 将List<V>按照V的methodName方法返回值(返回值必须为K类型)分组,合入到Map<K, List<V>>中<br>
* 要保证入参的method必须为V的某一个有返回值的方法,并且该返回值必须为K类型
*
* @param list
* 待分组的列表
* @param map
* 存放分组后的map
* @param clazz
* 泛型V的类型
* @param methodName
* 方法名
*/
public static <K, V> void listGroup2Map(List<V> list, Map<K, List<V>> map, Class<V> clazz, String methodName) {
// 入参非法行校验
if (null == list || null == map || null == clazz || !ParamUtils.chkString(methodName)) {
System.out.print("CommonUtils.listGroup2Map 入参错误,list:" + list + " ;map:" + map + " ;clazz:" + clazz + " ;methodName:" + methodName);
return;
} // 获取方法
Method method = getMethodByName(clazz, methodName);
// 非空判断
if (null == method) {
return;
} // 正式分组
listGroup2Map(list, map, method);
}
/**
* 根据类和方法名,获取方法对象
*
* @param clazz
* @param methodName
* @return
*/
public static Method getMethodByName(Class<?> clazz, String methodName) {
Method method = null;
// 入参不能为空
if (null == clazz || !ParamUtils.chkString(methodName)) {
System.out.print("CommonUtils.getMethodByName 入参错误,clazz:" + clazz + " ;methodName:" + methodName);
return method;
} try {
method = clazz.getDeclaredMethod(methodName);
} catch (Exception e) {
System.out.print("类获取方法失败!");
} return method;
}
/**
* 将List<V>按照V的某个方法返回值(返回值必须为K类型)分组,合入到Map<K, List<V>>中<br>
* 要保证入参的method必须为V的某一个有返回值的方法,并且该返回值必须为K类型
*
* @param list
* 待分组的列表
* @param map
* 存放分组后的map
* @param method
* 方法
*/
@SuppressWarnings("unchecked")
public static <K, V> void listGroup2Map(List<V> list, Map<K, List<V>> map, Method method) {
// 入参非法行校验
if (null == list || null == map || null == method) {
System.out.print("CommonUtils.listGroup2Map 入参错误,list:" + list + " ;map:" + map + " ;method:" + method);
return;
} try {
// 开始分组
Object key;
List<V> listTmp;
for (V val : list) {
key = method.invoke(val);
listTmp = map.get(key);
if (null == listTmp) {
listTmp = new ArrayList<V>();
map.put((K) key, listTmp);
}
listTmp.add(val);
}
} catch (Exception e) {
System.out.print("分组失败!");
}
}
}
测试类
- import java.util.ArrayList;
- import java.util.LinkedHashMap;
- import java.util.List;
- import java.util.Map;
- import com.framework.common.CommonUtils.GroupBy;
- public class Test {
- /**
- * @param args
- */
- public static void main(String[] args) {
- // 准备一个集合
- final int loop = 1000 * 1000;
- List<Data> list = new ArrayList<Data>(); // size=8 * loop
- for (int i = 0; i < loop; i++) {
- list.add(new Data().setId(1L).setCourseId(200010L).setContent("AAA"));
- list.add(new Data().setId(2L).setCourseId(200010L).setContent("BBB"));
- list.add(new Data().setId(3L).setCourseId(200011L).setContent("CCC"));
- list.add(new Data().setId(4L).setCourseId(200011L).setContent("DDD"));
- list.add(new Data().setId(5L).setCourseId(200010L).setContent("EEE"));
- list.add(new Data().setId(6L).setCourseId(200011L).setContent("FFF"));
- list.add(new Data().setId(7L).setCourseId(200010L).setContent("GGG"));
- list.add(new Data().setId(8L).setCourseId(200012L).setContent("HHH"));
- }
- // 进行分组 1
- long time = System.currentTimeMillis();
- Map<Long, List<Data>> map2 = new LinkedHashMap<Long, List<Data>>();
- CommonUtils.listGroup2Map(list, map2, Data.class, "getId");// 输入方法名
- long duration = System.currentTimeMillis() - time;
- System.out.println("分组一执行:" + duration + "毫秒!");
- // 分组二
- time = System.currentTimeMillis();
- Map<Long, List<Data>> map = CommonUtils.group(list, new GroupBy<Long>() {
- @Override
- public Long groupby(Object obj) {
- Data d = (Data) obj;
- return d.getCourseId(); // 分组依据为课程ID
- }
- });
- duration = System.currentTimeMillis() - time;
- System.out.println("分组二执行:" + duration + "毫秒!");
- }
- }

import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map; import com.framework.common.CommonUtils.GroupBy; public class Test {/**
* @param args
*/
public static void main(String[] args) {
// 准备一个集合 final int loop = 1000 * 1000;
List<Data> list = new ArrayList<Data>(); // size=8 * loop
for (int i = 0; i < loop; i++) {
list.add(new Data().setId(1L).setCourseId(200010L).setContent("AAA"));
list.add(new Data().setId(2L).setCourseId(200010L).setContent("BBB"));
list.add(new Data().setId(3L).setCourseId(200011L).setContent("CCC"));
list.add(new Data().setId(4L).setCourseId(200011L).setContent("DDD"));
list.add(new Data().setId(5L).setCourseId(200010L).setContent("EEE"));
list.add(new Data().setId(6L).setCourseId(200011L).setContent("FFF"));
list.add(new Data().setId(7L).setCourseId(200010L).setContent("GGG"));
list.add(new Data().setId(8L).setCourseId(200012L).setContent("HHH"));
}
// 进行分组 1
long time = System.currentTimeMillis();
Map<Long, List<Data>> map2 = new LinkedHashMap<Long, List<Data>>();
CommonUtils.listGroup2Map(list, map2, Data.class, "getId");// 输入方法名 long duration = System.currentTimeMillis() - time; System.out.println("分组一执行:" + duration + "毫秒!"); // 分组二
time = System.currentTimeMillis();
Map<Long, List<Data>> map = CommonUtils.group(list, new GroupBy<Long>() {
@Override
public Long groupby(Object obj) {
Data d = (Data) obj;
return d.getCourseId(); // 分组依据为课程ID
}
}); duration = System.currentTimeMillis() - time; System.out.println("分组二执行:" + duration + "毫秒!"); }
}
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