JavaScript有Array.join()
js>["Bill","Bob","Steve"].join(" and ")
Bill and Bob and Steve
Java有这样的东西吗?我知道我可以用StringBuilder自己拼凑一些东西:
static public String join(List<String> list, String conjunction)
{
StringBuilder sb = new StringBuilder();
boolean first = true;
for (String item : list)
{
if (first)
first = false;
else
sb.append(conjunction);
sb.append(item);
}
return sb.toString();
}
. .但是如果像这样的东西已经是JDK的一部分，那么这样做就没有意义了。
当前回答
另一个解，它是另一个答案的变体
public static String concatStringsWSep(Iterable<String> strings, String separator) {
Iterator<String> it = strings.iterator();
if( !it.hasNext() ) return "";
StringBuilder sb = new StringBuilder(it.next());
while( it.hasNext()) {
sb.append(separator).append(it.next());
}
return sb.toString();
}
其他回答
Java 8中有三种可能性:
List<String> list = Arrays.asList("Alice", "Bob", "Charlie")
String result = String.join(" and ", list);
result = list.stream().collect(Collectors.joining(" and "));
result = list.stream().reduce((t, u) -> t + " and " + u).orElse("");
谷歌的Guava API也有.join()，尽管(从其他回复中应该很明显)，Apache Commons在这里几乎是标准的。
使用Java .util. stringjoiner的Java 8解决方案
Java 8有一个StringJoiner类。但您仍然需要编写一些样板文件，因为它是Java。
StringJoiner sj = new StringJoiner(" and ", "" , "");
String[] names = {"Bill", "Bob", "Steve"};
for (String name : names) {
sj.add(name);
}
System.out.println(sj);
你可以从Spring框架的StringUtils中使用它。我知道它已经被提到过，但是实际上您可以只使用这段代码，它就可以立即工作，而不需要Spring。
// from https://github.com/spring-projects/spring-framework/blob/master/spring-core/src/main/java/org/springframework/util/StringUtils.java
/*
* Copyright 2002-2017 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
public class StringUtils {
public static String collectionToDelimitedString(Collection<?> coll, String delim, String prefix, String suffix) {
if(coll == null || coll.isEmpty()) {
return "";
}
StringBuilder sb = new StringBuilder();
Iterator<?> it = coll.iterator();
while (it.hasNext()) {
sb.append(prefix).append(it.next()).append(suffix);
if (it.hasNext()) {
sb.append(delim);
}
}
return sb.toString();
}
}
所有对Apache Commons的引用都很好(这是大多数人使用的)，但我认为与Guava相当的Joiner具有更好的API。
你可以使用简单的连接
Joiner.on(" and ").join(names)
但也很容易处理空值:
Joiner.on(" and ").skipNulls().join(names);
or
Joiner.on(" and ").useForNull("[unknown]").join(names);
和(就我而言，它比common -lang更有用)，处理map的能力:
Map<String, Integer> ages = .....;
String foo = Joiner.on(", ").withKeyValueSeparator(" is ").join(ages);
// Outputs:
// Bill is 25, Joe is 30, Betty is 35
这对于调试等非常有用。
