List转为Map

List转为Map

1、业务需求，需要将List<SysSetting>转为Map

SysSetting是一个对象

@Data
@TableName("t_sys_setting")
@ApiModel(value = "SysSetting对象", description = "系统设置表")
public class SysSetting implements Serializable {

    private static final long serialVersionUID = 1L;

    @TableId(value = "id", type = IdType.AUTO)
    private Long id;

    @ApiModelProperty("类型 10：交易设置 20：提现设置 30：签到设置")
    private String type;

    @ApiModelProperty(value = "键")
    @TableField("`key`")
    private String key;

    @ApiModelProperty(value = "值")
    private String value;

    @ApiModelProperty(value = "描述")
    private String description;

}

2、我们需要用到一个CollectionUtils，具体操作如下：

List<SysSetting> sysSettings = iSysSettingService.listSettingByCondition(SysSettingConstants.TYPE_SIGN);
Map<String, SysSetting> settingMap = CollectionUtils.convertMap(sysSettings, SysSetting::getKey);

convertMap方法如下。传参时param1：List<Entity>对象，param2：Entity的属性

    /**
     * List转Map（Map的值为List）
     *
     * @param from    List对象
     * @param keyFunc Map的键
     * @param <T>     List对象类型
     * @param <K>     键类型
     * @return map
     */
    public static <T, K> Map<K, T> convertMap(List<T> from, Function<T, K> keyFunc) {
        return from.stream().collect(Collectors.toMap(keyFunc, Function.identity()));
    }

得到的：Map<Entity::属性，Entity>

3、这样就完成了转换，下面我们看一下具体的效果。

转换之前List<SysSetting>

syssettings[
SysSetting(id=13, type=sign, key=sign_cycle, 	     value=7, description=签到周期), 
SysSetting(id=14, type=sign, key=sign_reward_points, value=10, description=每日签到奖励-积分), 
SysSetting(id=15, type=sign, key=sign_reward_exp,    value=10, description=每日签到奖励-成长值), 
SysSetting(id=16, type=sign, key=sign_cont_json,     value=[
      {
        "signCycle": 2,
        "rewardPoints": 20,
        "rewardExp": 20
      },
      {
        "signCycle": 3,
        "rewardPoints": 40,
        "rewardExp": 40
      },
      {
        "signCycle": 6,
        "rewardPoints": 60,
        "rewardExp": 60
      }
    ], description=连续签到Json)]

转换之后Map<Entity::属性，Entity>

settingmap{
sign_reward_points = SysSetting(id=14, type=sign, key=sign_reward_points, value=10, description=每日签到奖励-积分), 
sign_cont_json     = SysSetting(id=16, type=sign, key=sign_cont_json, value=[
      {
        "signCycle": 2,
        "rewardPoints": 20,
        "rewardExp": 20
      },
      {
        "signCycle": 3,
        "rewardPoints": 40,
        "rewardExp": 40
      },
      {
        "signCycle": 6,
        "rewardPoints": 60,
        "rewardExp": 60
      }
    ], description=连续签到Json), 
sign_reward_exp     =  SysSetting(id=15, type=sign, key=sign_reward_exp, value=10, description=每日签到奖励-成长值),
sign_cycle			=  SysSetting(id=13, type=sign, key=sign_cycle, value=7, description=签到周期)}

4、CollectionUtils扩展

 /**
     * List转Map（Map的值为List对象的某个属性）
     *
     * @param from      List对象
     * @param keyFunc   Map的键
     * @param valueFunc Map的值
     * @param <T>       List对象类型
     * @param <K>       键类型
     * @param <V>       值类型
     * @return map
     */
    public static <T, K, V> Map<K, V> convertMap(List<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc) {
        return from.stream().collect(Collectors.toMap(keyFunc, valueFunc));
    }

    public static <T, K, V> Map<K, List<V>> convertMultiMap(List<T> from, Function<T, K> keyFunc, Function<T, V> valueFunc) {
        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) {
        return from.stream().collect(Collectors.groupingBy(keyFunc, Collectors.mapping(valueFunc, Collectors.toSet())));
    }

    public static boolean containsAny(Collection<?> source, Collection<?> candidates) {
        return org.springframework.util.CollectionUtils.containsAny(source, candidates);
    }