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平常在工作中经常用到, List 向Map转换,

或者转换成 Map<Key, Map<Key2, Val >>,

也有转换成 Map<K, List<V>>,

方便分组提取数据, 虽然在jdk 1.8后有其它方法, 但是还是觉得工具类用起来方便, 下面就是代码实现:

package test;import java.lang.reflect.InvocationTargetException;import java.lang.reflect.Method;import java.util.ArrayList;import java.util.HashMap;import java.util.List;import java.util.Map;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;import org.springframework.util.CollectionUtils;/**  * 将List转换为 Map的工具类 * @author guishuanglin 2020-04-20 */public class TestListToMap {	private static final Log logger = LogFactory.getLog(TestListToMap.class);		/**	 * 将List转换为 Map
   
    >	 * @param dataList 需要转换的数据	 * @param methodNameK  取K 值的方法名	 * @param methodNameK2   取K2 值的方法名	 * @return	 */	@SuppressWarnings({ "unchecked" })	public static 
    
      Map
     
      > ListToMapMap(List
      
        dataList, String methodNameK, String methodNameK2) {		if (CollectionUtils.isEmpty(dataList)) {			return null;		}		if (methodNameK == null || "".equals(methodNameK)) {			logger.error("param methodNameK is null");			return null;		}		if (methodNameK2 == null || "".equals(methodNameK2)) {			logger.error("param methodNameK2 is null");			return null;		}		Method m = null;		Method m2 = null;		V dataObj = dataList.get(0);		try {			m = dataObj.getClass().getDeclaredMethod(methodNameK);			m2 = dataObj.getClass().getDeclaredMethod(methodNameK2);		} catch (NoSuchMethodException e) {			logger.error("ListToMapMap error", e);		}		Map
       
        > dataMap = new HashMap
        
         >(); for (V data : dataList) { if(data != null){ try { K k = (K)m.invoke(data, new Object[]{}); K2 k2 = (K2)m2.invoke(data, new Object[]{}); Map
         
           temp = null; if (dataMap.containsKey(k)) { temp = dataMap.get(k); } else { temp = new HashMap
          
           (); dataMap.put(k, temp); } temp.put(k2, data); } catch (SecurityException e) { e.printStackTrace(); } catch (IllegalArgumentException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } catch (InvocationTargetException e) { e.printStackTrace(); } } } return dataMap; } /** * 将List转换为 Map
           
            > * @param dataList 需要转换的数据 * @param methodNameK 取K 值的方法名 * @return */ @SuppressWarnings({ "unchecked" }) public static 
            
              Map
             
              > ListToMapList(List
              
                dataList, String methodNameK) { if (CollectionUtils.isEmpty(dataList)) { return null; } if (methodNameK == null || "".equals(methodNameK)) { logger.error("param methodNameK is null"); return null; } Method method = null; V dataObj = dataList.get(0); try { method = dataObj.getClass().getDeclaredMethod(methodNameK); } catch (NoSuchMethodException e) { logger.error("ListToMapList error", e); } Map
               
                > dataMap = new HashMap
                
                 >(); for (V data : dataList) { if(data != null){ try { K k = (K)method.invoke(data, new Object[]{}); List
                 
                   temp = null; if (dataMap.containsKey(k)) { temp = dataMap.get(k); } else { temp = new ArrayList
                  
                   (); dataMap.put(k, temp); } temp.add(data); } catch (SecurityException e) { e.printStackTrace(); } catch (IllegalArgumentException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } catch (InvocationTargetException e) { e.printStackTrace(); } } } return dataMap; } /** * 将List转换为map * @param dataList 需要转换的数据 * @param methodNameK 取K 值的方法名 * @return */ @SuppressWarnings({ "unchecked" }) public static 
                   
                     Map
                    
                      ListToMap(List
                     
                       dataList, String methodNameK) { if (CollectionUtils.isEmpty(dataList)) { return null; } if (methodNameK == null || "".equals(methodNameK)) { logger.error("param methodNameKK is null"); return null; } Method method = null; V dataObj = dataList.get(0); try { method = dataObj.getClass().getDeclaredMethod(methodNameK); } catch (NoSuchMethodException e) { logger.error("ListToMapList error", e); } Map
                      
                        dataMap = new HashMap
                       
                        (); for (V data : dataList) { if(data != null){ try { K k = (K)method.invoke(data, new Object[]{}); dataMap.put(k, data); } catch (SecurityException e) { e.printStackTrace(); } catch (IllegalArgumentException e) { e.printStackTrace(); } catch (IllegalAccessException e) { e.printStackTrace(); } catch (InvocationTargetException e) { e.printStackTrace(); } } } return dataMap; } public static void main(String[] args) { //自己可以写测试代码 }}
                       
                      
                     
                    
                   
                  
                 
                
               
              
             
            
           
          
         
        
       
      
     
    
   

测试代码就不上了, 上面的类是完整的, 如果没有 springframework 包, 可以自己用代码判断是不是空List,

logging 包也不是必须的, 如果没有可以用java自己的输出.

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