如何使用方法参考/java归纳实用程序功能8 [英] How to generalize utility function using method references/java 8

问题描述

我遇到了一种常见情况，我有一个对象列表，需要生成一个具有单个属性的逗号分隔的字符串，然后每个字符串都用单引号引起来.

I've run into a common situation where i have a list of objects and need to generate a comma separated string with a single property, which are then each surrounded by single quotes.

2个示例

public String partIDsToString(List<Part> parts){
    StringBuilder sb = new StringBuilder();
    for(Part part : parts)
        sb.append("'"+part.getPartNumber() + "',");
    return sb.substring(0,sb.length()-1);
}

public String companyIDsToString(List<Company> parts){
    StringBuilder sb = new StringBuilder();
    for(Company c : parts)
        sb.append("'"+c.getId() + "',");
    return sb.substring(0,sb.length()-1);
}

将来我将需要创建更多这样的方法，并且想知道是否有一种方法可以推广这种功能，我正在寻找这样的东西.

I'll need to create more methods like this in the future, and was wondering if there was a way to generalize this functionality, im looking for something like this.

public String objectPropertyToString(List<Object> list, Method getProperty){
    StringBuilder sb = new StringBuilder();
    for(Object obj: list)
        sb.append("'"+obj.getProperty() + "',");
    return sb.substring(0,sb.length()-1);
}

List<Company> companies = getCompaniesList();//not important
String result = objectPropertyToString(companies , Company::getId);

List<Part> parts= getPartsList();//not important
String result = objectPropertyToString(parts, Part::getPartNumber);

可以使用方法引用/lambdas或任何其他方式来完成此操作吗?

Can this be done using method references/lambdas, or any other way?

推荐答案

Stream.map() and Collectors.joining() are your friends here.

companies.stream()
         .map(Company::getId)
         .map(s -> "'" + s + "'")
         .collect(joining(","));

您可以创建一个辅助方法，但是根据我的判断，以上内容很简洁，不值得:

You can create a helper method, but in my judgement the above is succinct enough that it isn't worthwhile:

static <T> String mapAndJoin(Collection<T> c, Function<T,String> f){
    return c.stream()
            .map(f)
            .map(s -> "'" + s + "'")
            .collect(joining(","));
}

mapAndJoin(companies, Company::getId);

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