新增基础组件

ktg-common/src/main/java/com/ktg/common/core/domain/BaseEntity.java

@@ -4,11 +4,13 @@ import java.io.Serializable;
 import java.util.Date;
 import java.util.HashMap;
 import java.util.Map;
+
+import com.baomidou.mybatisplus.annotation.TableField;
 import com.fasterxml.jackson.annotation.JsonFormat;
 
 /**
  * Entity基类
- * 
+ *
  * @author ruoyi
  */
 public class BaseEntity implements Serializable
@@ -16,6 +18,7 @@ public class BaseEntity implements Serializable
     private static final long serialVersionUID = 1L;
 
     /** 搜索值 */
+    @TableField(exist = false)
     private String searchValue;
 
     /** 创建者 */
@@ -36,6 +39,7 @@ public class BaseEntity implements Serializable
     private String remark;
 
     /** 请求参数 */
+    @TableField(exist = false)
     private Map<String, Object> params;
 
     public String getSearchValue()

ktg-common/src/main/java/com/ktg/common/exception/ErrorCode.java

@@ -0,0 +1,30 @@
+package com.ktg.common.exception;
+
+import lombok.Data;
+
+/**
+ * 错误码对象
+ *
+ * 全局错误码，占用 [0, 999], 参见 {@link GlobalErrorCodeConstants}
+ * 业务异常错误码，占用 [1 000 000 000, +∞)，参见 {@link ServiceErrorCodeRange}
+ *
+ * TODO 错误码设计成对象的原因，为未来的 i18 国际化做准备
+ */
+@Data
+public class ErrorCode {
+
+    /**
+     * 错误码
+     */
+    private final Integer code;
+    /**
+     * 错误提示
+     */
+    private final String msg;
+
+    public ErrorCode(Integer code, String message) {
+        this.code = code;
+        this.msg = message;
+    }
+
+}

ktg-common/src/main/java/com/ktg/common/exception/ServiceException.java

@@ -1,8 +1,10 @@
 package com.ktg.common.exception;
 
+import com.ktg.common.pojo.CommonResult;
+
 /**
  * 业务异常
- * 
+ *
  * @author ruoyi
  */
 public final class ServiceException extends RuntimeException
@@ -44,6 +46,11 @@ public final class ServiceException extends RuntimeException
         this.code = code;
     }
 
+    public ServiceException(Integer code, String message) {
+        this.code = code;
+        this.message = message;
+    }
+
     public String getDetailMessage()
     {
         return detailMessage;
@@ -70,4 +77,4 @@ public final class ServiceException extends RuntimeException
         this.detailMessage = detailMessage;
         return this;
     }
-}
+}

ktg-common/src/main/java/com/ktg/common/exception/enums/GlobalErrorCodeConstants.java

@@ -0,0 +1,44 @@
+package com.ktg.common.exception.enums;
+
+
+import com.ktg.common.exception.ErrorCode;
+
+/**
+ * 全局错误码枚举
+ * 0-999 系统异常编码保留
+ *
+ * 一般情况下，使用 HTTP 响应状态码 https://developer.mozilla.org/zh-CN/docs/Web/HTTP/Status
+ * 虽然说，HTTP 响应状态码作为业务使用表达能力偏弱，但是使用在系统层面还是非常不错的
+ * 比较特殊的是，因为之前一直使用 0 作为成功，就不使用 200 啦。
+ *
+ * @author 智工委源码
+ */
+public interface GlobalErrorCodeConstants {
+
+    ErrorCode SUCCESS = new ErrorCode(0, "成功");
+
+    // ========== 客户端错误段 ==========
+
+    ErrorCode BAD_REQUEST = new ErrorCode(400, "请求参数不正确");
+    ErrorCode UNAUTHORIZED = new ErrorCode(401, "账号未登录");
+    ErrorCode FORBIDDEN = new ErrorCode(403, "没有该操作权限");
+    ErrorCode NOT_FOUND = new ErrorCode(404, "请求未找到");
+    ErrorCode METHOD_NOT_ALLOWED = new ErrorCode(405, "请求方法不正确");
+    ErrorCode LOCKED = new ErrorCode(423, "请求失败，请稍后重试"); // 并发请求，不允许
+    ErrorCode TOO_MANY_REQUESTS = new ErrorCode(429, "请求过于频繁，请稍后重试");
+
+    // ========== 服务端错误段 ==========
+
+    ErrorCode INTERNAL_SERVER_ERROR = new ErrorCode(500, "系统异常");
+    ErrorCode NOT_IMPLEMENTED = new ErrorCode(501, "功能未实现/未开启");
+    ErrorCode ERROR_CONFIGURATION = new ErrorCode(502, "错误的配置项");
+
+    // ========== 自定义错误段 ==========
+    ErrorCode REPEATED_REQUESTS = new ErrorCode(900, "重复请求，请稍后重试"); // 重复请求
+    ErrorCode DEMO_DENY = new ErrorCode(901, "演示模式，禁止写操作");
+
+    ErrorCode ASSERT_ERROR = new ErrorCode(902, "断言异常");
+
+    ErrorCode UNKNOWN = new ErrorCode(999, "未知错误");
+
+}

ktg-common/src/main/java/com/ktg/common/pojo/CommonResult.java

@@ -0,0 +1,112 @@
+package com.ktg.common.pojo;
+
+import com.fasterxml.jackson.annotation.JsonIgnore;
+import com.ktg.common.exception.ErrorCode;
+import com.ktg.common.exception.ServiceException;
+import com.ktg.common.exception.enums.GlobalErrorCodeConstants;
+import lombok.Data;
+import org.springframework.util.Assert;
+
+import java.io.Serializable;
+import java.util.Objects;
+
+/**
+ * 通用返回
+ *
+ * @param <T> 数据泛型
+ */
+@Data
+public class CommonResult<T> implements Serializable {
+
+    /**
+     * 错误码
+     *
+     * @see ErrorCode#getCode()
+     */
+    private Integer code;
+    /**
+     * 返回数据
+     */
+    private T data;
+    /**
+     * 错误提示，用户可阅读
+     *
+     * @see ErrorCode#getMsg() ()
+     */
+    private String msg;
+
+    /**
+     * 将传入的 result 对象，转换成另外一个泛型结果的对象
+     *
+     * 因为 A 方法返回的 CommonResult 对象，不满足调用其的 B 方法的返回，所以需要进行转换。
+     *
+     * @param result 传入的 result 对象
+     * @param <T>    返回的泛型
+     * @return 新的 CommonResult 对象
+     */
+    public static <T> CommonResult<T> error(CommonResult<?> result) {
+        return error(result.getCode(), result.getMsg());
+    }
+
+    public static <T> CommonResult<T> error(Integer code, String message) {
+        Assert.isTrue(!GlobalErrorCodeConstants.SUCCESS.getCode().equals(code), "code 必须是错误的！");
+        CommonResult<T> result = new CommonResult<>();
+        result.code = code;
+        result.msg = message;
+        return result;
+    }
+
+    public static <T> CommonResult<T> error(ErrorCode errorCode) {
+        return error(errorCode.getCode(), errorCode.getMsg());
+    }
+
+    public static <T> CommonResult<T> success(T data) {
+        CommonResult<T> result = new CommonResult<>();
+        result.code = GlobalErrorCodeConstants.SUCCESS.getCode();
+        result.data = data;
+        result.msg = "";
+        return result;
+    }
+
+    public static boolean isSuccess(Integer code) {
+        return Objects.equals(code, GlobalErrorCodeConstants.SUCCESS.getCode());
+    }
+
+    @JsonIgnore // 避免 jackson 序列化
+    public boolean isSuccess() {
+        return isSuccess(code);
+    }
+
+    @JsonIgnore // 避免 jackson 序列化
+    public boolean isError() {
+        return !isSuccess();
+    }
+
+    // ========= 和 Exception 异常体系集成 =========
+
+    /**
+     * 判断是否有异常。如果有，则抛出 {@link ServiceException} 异常
+     */
+    public void checkError() throws ServiceException {
+        if (isSuccess()) {
+            return;
+        }
+        // 业务异常
+        throw new ServiceException(code, msg);
+    }
+
+    /**
+     * 判断是否有异常。如果有，则抛出 {@link ServiceException} 异常
+     * 如果没有，则返回 {@link #data} 数据
+     */
+    @JsonIgnore // 避免 jackson 序列化
+    public T getCheckedData() {
+        checkError();
+        return data;
+    }
+
+    public static <T> CommonResult<T> error(ServiceException serviceException) {
+        return error(serviceException.getCode(), serviceException.getMessage());
+    }
+
+}

ktg-common/src/main/java/com/ktg/common/utils/bean/BeanUtils.java

@@ -1,14 +1,18 @@
 package com.ktg.common.utils.bean;
 
+import cn.hutool.core.bean.BeanUtil;
+import com.ktg.common.pojo.PageResult;
+
 import java.lang.reflect.Method;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.Consumer;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 
 /**
  * Bean 工具类
- * 
+ *
  * @author ruoyi
  */
 public class BeanUtils extends org.springframework.beans.BeanUtils
@@ -24,7 +28,7 @@ public class BeanUtils extends org.springframework.beans.BeanUtils
 
     /**
      * Bean属性复制工具方法。
-     * 
+     *
      * @param dest 目标对象
      * @param src 源对象
      */
@@ -42,7 +46,7 @@ public class BeanUtils extends org.springframework.beans.BeanUtils
 
     /**
      * 获取对象的setter方法。
-     * 
+     *
      * @param obj 对象
      * @return 对象的setter方法列表
      */
@@ -70,7 +74,7 @@ public class BeanUtils extends org.springframework.beans.BeanUtils
 
     /**
      * 获取对象的getter方法。
-     * 
+     *
      * @param obj 对象
      * @return 对象的getter方法列表
      */
@@ -97,7 +101,7 @@ public class BeanUtils extends org.springframework.beans.BeanUtils
     /**
      * 检查Bean方法名中的属性名是否相等。<br>
      * 如getName()和setName()属性名一样，getName()和setAge()属性名不一样。
-     * 
+     *
      * @param m1 方法名1
      * @param m2 方法名2
      * @return 属性名一样返回true，否则返回false
@@ -107,4 +111,49 @@ public class BeanUtils extends org.springframework.beans.BeanUtils
     {
         return m1.substring(BEAN_METHOD_PROP_INDEX).equals(m2.substring(BEAN_METHOD_PROP_INDEX));
     }
+
+
+    public static <T> T toBean(Object source, Class<T> targetClass) {
+        return BeanUtil.toBean(source, targetClass);
+    }
+
+    public static <T> T toBean(Object source, Class<T> targetClass, Consumer<T> peek) {
+        T target = toBean(source, targetClass);
+        if (target != null) {
+            peek.accept(target);
+        }
+        return target;
+    }
+
+    public static <S, T> List<T> toBean(List<S> source, Class<T> targetType) {
+        if (source == null) {
+            return null;
+        }
+        return CollectionUtils.convertList(source, s -> toBean(s, targetType));
+    }
+
+    public static <S, T> List<T> toBean(List<S> source, Class<T> targetType, Consumer<T> peek) {
+        List<T> list = toBean(source, targetType);
+        if (list != null) {
+            list.forEach(peek);
+        }
+        return list;
+    }
+
+    public static <S, T> PageResult<T> toBean(PageResult<S> source, Class<T> targetType) {
+        return toBean(source, targetType, null);
+    }
+
+    public static <S, T> PageResult<T> toBean(PageResult<S> source, Class<T> targetType, Consumer<T> peek) {
+        if (source == null) {
+            return null;
+        }
+        List<T> list = toBean(source.getList(), targetType);
+        if (peek != null) {
+            list.forEach(peek);
+        }
+        return new PageResult<>(list, source.getTotal());
+    }
+
+
 }

ktg-common/src/main/java/com/ktg/common/utils/bean/CollectionUtils.java

@@ -0,0 +1,318 @@
+package com.ktg.common.utils.bean;
+
+import cn.hutool.core.collection.CollUtil;
+import cn.hutool.core.collection.CollectionUtil;
+import cn.hutool.core.util.ArrayUtil;
+import com.google.common.collect.ImmutableMap;
+
+import java.util.*;
+import java.util.function.*;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import static java.util.Arrays.asList;
+
+/**
+ * Collection 工具类
+ *
+ * @author cc
+ */
+public class CollectionUtils {
+
+    public static boolean containsAny(Object source, Object... targets) {
+        return asList(targets).contains(source);
+    }
+
+    public static boolean isAnyEmpty(Collection<?>... collections) {
+        return Arrays.stream(collections).anyMatch(CollectionUtil::isEmpty);
+    }
+
+    public static <T> boolean anyMatch(Collection<T> from, Predicate<T> predicate) {
+        return from.stream().anyMatch(predicate);
+    }
+
+    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, R> List<T> distinct(Collection<T> from, Function<T, R> keyMapper) {
+        if (CollUtil.isEmpty(from)) {
+            return new ArrayList<>();
+        }
+        return distinct(from, keyMapper, (t1, t2) -> t1);
+    }
+
+    public static <T, R> List<T> distinct(Collection<T> from, Function<T, R> keyMapper, BinaryOperator<T> cover) {
+        if (CollUtil.isEmpty(from)) {
+            return new ArrayList<>();
+        }
+        return new ArrayList<>(convertMap(from, keyMapper, Function.identity(), cover).values());
+    }
+
+    public static <T, U> List<U> convertList(T[] from, Function<T, U> func) {
+        if (ArrayUtil.isEmpty(from)) {
+            return new ArrayList<>();
+        }
+        return convertList(Arrays.asList(from), func);
+    }
+
+    public static <T, U> List<U> convertList(Collection<T> from, Function<T, U> func) {
+        if (CollUtil.isEmpty(from)) {
+            return new ArrayList<>();
+        }
+        return from.stream().map(func).filter(Objects::nonNull).collect(Collectors.toList());
+    }
+
+    public static <T, U> List<U> convertList(Collection<T> from, Function<T, U> func, Predicate<T> filter) {
+        if (CollUtil.isEmpty(from)) {
+            return new ArrayList<>();
+        }
+        return from.stream().filter(filter).map(func).filter(Objects::nonNull).collect(Collectors.toList());
+    }
+
+    public static <T, U> List<U> convertListByFlatMap(Collection<T> from,
+                                                      Function<T, ? extends Stream<? extends U>> func) {
+        if (CollUtil.isEmpty(from)) {
+            return new ArrayList<>();
+        }
+        return from.stream().flatMap(func).filter(Objects::nonNull).collect(Collectors.toList());
+    }
+
+    public static <T, U, R> List<R> convertListByFlatMap(Collection<T> from,
+                                                         Function<? super T, ? extends U> mapper,
+                                                         Function<U, ? extends Stream<? extends R>> func) {
+        if (CollUtil.isEmpty(from)) {
+            return new ArrayList<>();
+        }
+        return from.stream().map(mapper).flatMap(func).filter(Objects::nonNull).collect(Collectors.toList());
+    }
+
+    public static <K, V> List<V> mergeValuesFromMap(Map<K, List<V>> map) {
+        return map.values()
+                .stream()
+                .flatMap(List::stream)
+                .collect(Collectors.toList());
+    }
+
+    public static <T, U> Set<U> convertSet(Collection<T> from, Function<T, U> func) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashSet<>();
+        }
+        return from.stream().map(func).filter(Objects::nonNull).collect(Collectors.toSet());
+    }
+
+    public static <T, U> Set<U> convertSet(Collection<T> from, Function<T, U> func, Predicate<T> filter) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashSet<>();
+        }
+        return from.stream().filter(filter).map(func).filter(Objects::nonNull).collect(Collectors.toSet());
+    }
+
+    public static <T, K> Map<K, T> convertMapByFilter(Collection<T> from, Predicate<T> filter, Function<T, K> keyFunc) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashMap<>();
+        }
+        return from.stream().filter(filter).collect(Collectors.toMap(keyFunc, v -> v));
+    }
+
+    public static <T, U> Set<U> convertSetByFlatMap(Collection<T> from,
+                                                    Function<T, ? extends Stream<? extends U>> func) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashSet<>();
+        }
+        return from.stream().flatMap(func).filter(Objects::nonNull).collect(Collectors.toSet());
+    }
+
+    public static <T, U, R> Set<R> convertSetByFlatMap(Collection<T> from,
+                                                       Function<? super T, ? extends U> mapper,
+                                                       Function<U, ? extends Stream<? extends R>> func) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashSet<>();
+        }
+        return from.stream().map(mapper).flatMap(func).filter(Objects::nonNull).collect(Collectors.toSet());
+    }
+
+    public static <T, K> Map<K, T> convertMap(Collection<T> from, Function<T, K> keyFunc) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashMap<>();
+        }
+        return convertMap(from, keyFunc, Function.identity());
+    }
+
+    public static <T, K> Map<K, T> convertMap(Collection<T> from, Function<T, K> keyFunc, Supplier<? extends Map<K, T>> supplier) {
+        if (CollUtil.isEmpty(from)) {
+            return supplier.get();
+        }
+        return convertMap(from, keyFunc, Function.identity(), supplier);
+    }
+
+    public static <T, K, V> Map<K, V> convertMap(Collection<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashMap<>();
+        }
+        return convertMap(from, keyFunc, valueFunc, (v1, v2) -> v1);
+    }
+
+    public static <T, K, V> Map<K, V> convertMap(Collection<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc, BinaryOperator<V> mergeFunction) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashMap<>();
+        }
+        return convertMap(from, keyFunc, valueFunc, mergeFunction, HashMap::new);
+    }
+
+    public static <T, K, V> Map<K, V> convertMap(Collection<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc, Supplier<? extends Map<K, V>> supplier) {
+        if (CollUtil.isEmpty(from)) {
+            return supplier.get();
+        }
+        return convertMap(from, keyFunc, valueFunc, (v1, v2) -> v1, supplier);
+    }
+
+    public static <T, K, V> Map<K, V> convertMap(Collection<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc, BinaryOperator<V> mergeFunction, Supplier<? extends Map<K, V>> supplier) {
+        if (CollUtil.isEmpty(from)) {
+            return new HashMap<>();
+        }
+        return from.stream().collect(Collectors.toMap(keyFunc, valueFunc, mergeFunction, supplier));
+    }
+
+    public static <T, K> Map<K, List<T>> convertMultiMap(Collection<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(Collection<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(Collection<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())));
+    }
+
+    public static <T, K> Map<K, T> convertImmutableMap(Collection<T> from, Function<T, K> keyFunc) {
+        if (CollUtil.isEmpty(from)) {
+            return Collections.emptyMap();
+        }
+        ImmutableMap.Builder<K, T> builder = ImmutableMap.builder();
+        from.forEach(item -> builder.put(keyFunc.apply(item), item));
+        return builder.build();
+    }
+
+    /**
+     * 对比老、新两个列表，找出新增、修改、删除的数据
+     *
+     * @param oldList  老列表
+     * @param newList  新列表
+     * @param sameFunc 对比函数，返回 true 表示相同，返回 false 表示不同
+     *                 注意，same 是通过每个元素的“标识”，判断它们是不是同一个数据
+     * @return [新增列表、修改列表、删除列表]
+     */
+    public static <T> List<List<T>> diffList(Collection<T> oldList, Collection<T> newList,
+                                             BiFunction<T, T, Boolean> sameFunc) {
+        List<T> createList = new LinkedList<>(newList); // 默认都认为是新增的，后续会进行移除
+        List<T> updateList = new ArrayList<>();
+        List<T> deleteList = new ArrayList<>();
+
+        // 通过以 oldList 为主遍历，找出 updateList 和 deleteList
+        for (T oldObj : oldList) {
+            // 1. 寻找是否有匹配的
+            T foundObj = null;
+            for (Iterator<T> iterator = createList.iterator(); iterator.hasNext(); ) {
+                T newObj = iterator.next();
+                // 1.1 不匹配，则直接跳过
+                if (!sameFunc.apply(oldObj, newObj)) {
+                    continue;
+                }
+                // 1.2 匹配，则移除，并结束寻找
+                iterator.remove();
+                foundObj = newObj;
+                break;
+            }
+            // 2. 匹配添加到 updateList；不匹配则添加到 deleteList 中
+            if (foundObj != null) {
+                updateList.add(foundObj);
+            } else {
+                deleteList.add(oldObj);
+            }
+        }
+        return asList(createList, updateList, deleteList);
+    }
+
+    public static boolean containsAny(Collection<?> source, Collection<?> candidates) {
+        return org.springframework.util.CollectionUtils.containsAny(source, candidates);
+    }
+
+    public static <T> T getFirst(List<T> from) {
+        return !CollectionUtil.isEmpty(from) ? from.get(0) : null;
+    }
+
+    public static <T> T findFirst(Collection<T> from, Predicate<T> predicate) {
+        return findFirst(from, predicate, Function.identity());
+    }
+
+    public static <T, U> U findFirst(Collection<T> from, Predicate<T> predicate, Function<T, U> func) {
+        if (CollUtil.isEmpty(from)) {
+            return null;
+        }
+        return from.stream().filter(predicate).findFirst().map(func).orElse(null);
+    }
+
+    public static <T, V extends Comparable<? super V>> V getMaxValue(Collection<T> from, Function<T, V> valueFunc) {
+        if (CollUtil.isEmpty(from)) {
+            return null;
+        }
+        assert !from.isEmpty(); // 断言，避免告警
+        T t = from.stream().max(Comparator.comparing(valueFunc)).get();
+        return valueFunc.apply(t);
+    }
+
+    public static <T, V extends Comparable<? super V>> V getMinValue(List<T> from, Function<T, V> valueFunc) {
+        if (CollUtil.isEmpty(from)) {
+            return null;
+        }
+        assert from.size() > 0; // 断言，避免告警
+        T t = from.stream().min(Comparator.comparing(valueFunc)).get();
+        return valueFunc.apply(t);
+    }
+
+    public static <T, V extends Comparable<? super V>> V getSumValue(List<T> from, Function<T, V> valueFunc,
+                                                                     BinaryOperator<V> accumulator) {
+        return getSumValue(from, valueFunc, accumulator, null);
+    }
+
+    public static <T, V extends Comparable<? super V>> V getSumValue(Collection<T> from, Function<T, V> valueFunc,
+                                                                     BinaryOperator<V> accumulator, V defaultValue) {
+        if (CollUtil.isEmpty(from)) {
+            return defaultValue;
+        }
+        assert !from.isEmpty(); // 断言，避免告警
+        return from.stream().map(valueFunc).filter(Objects::nonNull).reduce(accumulator).orElse(defaultValue);
+    }
+
+    public static <T> void addIfNotNull(Collection<T> coll, T item) {
+        if (item == null) {
+            return;
+        }
+        coll.add(item);
+    }
+
+    public static <T> Collection<T> singleton(T obj) {
+        return obj == null ? Collections.emptyList() : Collections.singleton(obj);
+    }
+
+    public static <T> List<T> newArrayList(List<List<T>> list) {
+        return list.stream().flatMap(Collection::stream).collect(Collectors.toList());
+    }
+
+}