1. 完成用户导出的功能

2. 完成前后端的导出的封装

src/main/java/cn/iocoder/dashboard/util/collection/CollectionUtils.java

@@ -1,5 +1,6 @@
 package cn.iocoder.dashboard.util.collection;
 
+import cn.hutool.core.collection.CollUtil;
 import cn.hutool.core.collection.CollectionUtil;
 
 import java.util.*;
@@ -19,37 +20,61 @@ public class CollectionUtils {
     }
 
     public static <T> List<T> filterList(Collection<T> from, Predicate<T> predicate) {
+        if (CollUtil.isEmpty(from)) {
+            return new ArrayList<>();
+        }
         return from.stream().filter(predicate).collect(Collectors.toList());
     }
 
     public static <T, U> List<U> convertList(List<T> from, Function<T, U> func) {
+        if (CollUtil.isEmpty(from)) {
+            return new ArrayList<>();
+        }
         return from.stream().map(func).collect(Collectors.toList());
     }
 
     public static <T, U> Set<U> convertSet(List<T> from, Function<T, U> func) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashSet<>();
+        }
         return from.stream().map(func).collect(Collectors.toSet());
     }
 
     public static <T, K> Map<K, T> convertMap(List<T> from, Function<T, K> keyFunc) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashMap<>();
+        }
         return from.stream().collect(Collectors.toMap(keyFunc, item -> item));
     }
 
     public static <T, K, V> Map<K, V> convertMap(List<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashMap<>();
+        }
         return from.stream().collect(Collectors.toMap(keyFunc, valueFunc));
     }
 
     public static <T, K> Map<K, List<T>> convertMultiMap(List<T> from, Function<T, K> keyFunc) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashMap<>();
+        }
         return from.stream().collect(Collectors.groupingBy(keyFunc,
                 Collectors.mapping(t -> t, Collectors.toList())));
     }
 
     public static <T, K, V> Map<K, List<V>> convertMultiMap(List<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashMap<>();
+        }
         return from.stream().collect(Collectors.groupingBy(keyFunc,
                 Collectors.mapping(valueFunc, Collectors.toList())));
     }
 
     // 暂时没想好名字，先以 2 结尾噶
     public static <T, K, V> Map<K, Set<V>> convertMultiMap2(List<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashMap<>();
+        }
         return from.stream().collect(Collectors.groupingBy(keyFunc, Collectors.mapping(valueFunc, Collectors.toSet())));
     }