一、背景

在用java8开发的时候，存在一些场景，如查询时，根据入参中的某个字段，如果不为空，则根据该字段进行过滤。
原代码类似：

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@Data
@AllArgsConstructor
class People
{
    private String name;

    private String city;

    private int age;
}

@Data
@AllArgsConstructor
class SearchRequest
{
    private String namePrefix;

    private String city;
}

// 某个过滤方法
private static List<People> filterDemo1(SearchRequest request)
{
    if (request == null)
    {
        return Lists.newArrayList();
    }
    List<People> peopleList = Lists.newArrayList();
    peopleList.add(new People("张三", "北京", 20));
    peopleList.add(new People("张四", "上海", 30));
    peopleList.add(new People("王五", "广州", 40));
    peopleList.add(new People("小明", "深圳", 50));

    List<People> filterByNameList = Lists.newArrayList();
    if (StringUtils.isNotEmpty(request.getNamePrefix()))
    {
        filterByNameList = peopleList.stream()
            .filter(p -> StringUtils.startsWith(p.getName(), request.getNamePrefix()))
            .collect(Collectors.toList());
    }
    else
    {
        filterByNameList = peopleList;
    }
    List<People> filterByCityList = Lists.newArrayList();
    if (StringUtils.isNotEmpty(request.getCity()))
    {
        filterByCityList = filterByNameList.stream()
            .filter(p -> StringUtils.equalsIgnoreCase(p.getName(), request.getCity()))
            .collect(Collectors.toList());
    }
    else
    {
        filterByCityList = filterByNameList;
    }
    return filterByCityList;
}

二、优雅实现

利用或运算短路运算符实现

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private static List<People> filterDemo2(SearchRequest request)
{
    if (request == null)
    {
        return Lists.newArrayList();
    }
    List<People> peopleList = Lists.newArrayList();
    peopleList.add(new People("张三", "北京", 20));
    peopleList.add(new People("张四", "上海", 30));
    peopleList.add(new People("王五", "广州", 40));
    peopleList.add(new People("小明", "深圳", 50));

    boolean needFilterByName = StringUtils.isNotEmpty(request.getNamePrefix());
    boolean needFilterByCity = StringUtils.isNotEmpty(request.getCity());
    return peopleList.stream()
        .filter(p -> !needFilterByName || StringUtils.startsWith(p.getName(), request.getNamePrefix()))
        .filter(p -> !needFilterByCity || StringUtils.equalsIgnoreCase(p.getName(), request.getCity()))
        .collect(Collectors.toList());
}