在 Java 8 中将 Map 连接到 String 的最优雅方式
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Most elegant way to join a Map to a String in Java 8
提问by tomaj
I love Guava, and I'll continue to use Guava a lot. But, where it makes sense, I try to use the "new stuff" in Java 8instead.
我喜欢Guava，我会继续大量使用 Guava 。但是，在有意义的地方，我尝试使用Java 8 中的“新东西” 。
"Problem"
“问题”
Lets say I want to join url attributes in a String. In GuavaI would do it like this:
假设我想将 url 属性加入String. 在番石榴中，我会这样做：
Map<String, String> attributes = new HashMap<>();
attributes.put("a", "1");
attributes.put("b", "2");
attributes.put("c", "3");
// Guava way
String result = Joiner.on("&").withKeyValueSeparator("=").join(attributes);
Where the resultis a=1&b=2&c=3.
凡result为a=1&b=2&c=3。
Question
问题
What is the most elegant way to do this in Java 8(without any 3rd party libraries)?
在Java 8 中执行此操作的最优雅方法是什么（没有任何 3rd 方库）？
回答by Alexis C.
You can grab the stream of the map's entry set, then map each entry to the string representation you want, joining them in a single string using Collectors.joining(CharSequence delimiter).
您可以获取地图条目集的流，然后将每个条目映射到您想要的字符串表示形式，并使用Collectors.joining(CharSequence delimiter).
import static java.util.stream.Collectors.joining;
String s = attributes.entrySet()
.stream()
.map(e -> e.getKey()+"="+e.getValue())
.collect(joining("&"));
But since the entry's toString()already output its content in the format key=value, you can call its toStringmethod directly:
但是由于条目toString()已经以 format 格式输出其内容key=value，您可以toString直接调用其方法：
String s = attributes.entrySet()
.stream()
.map(Object::toString)
.collect(joining("&"));
回答by Arpan Saini
public static void main(String[] args) {
HashMap<String,Integer> newPhoneBook = new HashMap(){{
putIfAbsent("Arpan",80186787);
putIfAbsent("Sanjay",80186788);
putIfAbsent("Kiran",80186789);
putIfAbsent("Pranjay",80186790);
putIfAbsent("Jaiparkash",80186791);
putIfAbsent("Maya",80186792);
putIfAbsent("Rythem",80186793);
putIfAbsent("Preeti",80186794);
}};
/**Compining Key and Value pairs and then separate each pair by some delimiter and the add prefix and Suffix*/
String keyValueCombinedString = newPhoneBook.entrySet().stream().
map(entrySet -> entrySet.getKey() + ":"+ entrySet.getValue()).
collect(Collectors.joining("," , "[","]"));
System.out.println(keyValueCombinedString);
/**
* OUTPUT : [Kiran:80186789,Arpan:80186787,Pranjay:80186790,Jaiparkash:80186791,Maya:80186792,Sanjay:80186788,Preeti:80186794,Rythem:80186793]
*
* */
String keyValueCombinedString1 = newPhoneBook.entrySet().stream().
map(Objects::toString).
collect(Collectors.joining("," , "[","]"));
System.out.println(keyValueCombinedString1);
/**
* Objects::toString method concate key and value pairs by =
* OUTPUT : [Kiran=80186789,Arpan=80186787,Pranjay=80186790,Jaiparkash=80186791,Maya=80186792,Sanjay=80186788,Preeti=80186794,Rythem=80186793]
* */
}
> Blockquote
