Java:将List <String>转换为String

Question

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自己解决一些问题:

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,那就没有意义了.

Answer 1

使用Java 8,您无需任何第三方库即可完成此操作.

如果要加入字符串集合,可以使用新的String.join()方法:

List<String> list = Arrays.asList("foo", "bar", "baz");
String joined = String.join(" and ", list); // "foo and bar and baz"

如果您的Collection类型与String不同,则可以将Stream API与加入的收集器一起使用:

List<Person> list = Arrays.asList(
  new Person("John", "Smith"),
  new Person("Anna", "Martinez"),
  new Person("Paul", "Watson ")
);

String joinedFirstNames = list.stream()
  .map(Person::getFirstName)
  .collect(Collectors.joining(", ")); // "John, Anna, Paul"

该StringJoiner课程也可能有用.

Answer 2

所有对Apache Commons的引用都很好(这是大多数人使用的)但我认为Guava等效的Joiner有一个更好的API.

您可以使用简单的连接案例

Joiner.on(" and ").join(names)

但也很容易处理空值:

Joiner.on(" and ").skipNulls().join(names);

要么

Joiner.on(" and ").useForNull("[unknown]").join(names);

并且(只要我关心使用它优先于commons-lang),处理地图的能力:

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.

Answer 3

没有开箱即用,但许多图书馆都有类似的:

Commons Lang:

org.apache.commons.lang.StringUtils.join(list, conjunction);

弹簧:

org.springframework.util.StringUtils.collectionToDelimitedString(list, conjunction);

Answer 4

在Android上,您可以使用TextUtils类.

TextUtils.join(" and ", names);

Answer 5

不,标准Java API中没有这样的便捷方法.

毫不奇怪,Apache Commons 在他们的StringUtils类中提供了这样的东西,以防你不想自己编写它.

Answer 6

Java 8中的三种可能性:

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("");

Answer 7

使用java 8收集器,可以使用以下代码完成:

Arrays.asList("Bill", "Bob", "Steve").stream()
.collect(Collectors.joining(" and "));

此外,Java 8中最简单的解决方案:

String.join(" and ", "Bill", "Bob", "Steve");

要么

String.join(" and ", Arrays.asList("Bill", "Bob", "Steve"));

Answer 8

我写了这个(我用它来bean和利用toString,所以不要写Collection<String>):

public static String join(Collection<?> col, String delim) {
    StringBuilder sb = new StringBuilder();
    Iterator<?> iter = col.iterator();
    if (iter.hasNext())
        sb.append(iter.next().toString());
    while (iter.hasNext()) {
        sb.append(delim);
        sb.append(iter.next().toString());
    }
    return sb.toString();
}

但是CollectionJSP不支持,所以对于TLD我写道:

public static String join(List<?> list, String delim) {
    int len = list.size();
    if (len == 0)
        return "";
    StringBuilder sb = new StringBuilder(list.get(0).toString());
    for (int i = 1; i < len; i++) {
        sb.append(delim);
        sb.append(list.get(i).toString());
    }
    return sb.toString();
}

并.tld存档:

<?xml version="1.0" encoding="UTF-8"?>
<taglib version="2.1" xmlns="http://java.sun.com/xml/ns/javaee"
    <function>
        <name>join</name>
        <function-class>com.core.util.ReportUtil</function-class>
        <function-signature>java.lang.String join(java.util.List, java.lang.String)</function-signature>
    </function>
</taglib>

并在JSP文件中使用它:

<%@taglib prefix="funnyFmt" uri="tag:com.core.util,2013:funnyFmt"%>
${funnyFmt:join(books, ", ")}

Answer 9

如果您想在没有任何外部库的情况下使用JDK,那么您拥有的代码是正确的方法.您可以在JDK中使用简单的"单行".

如果您可以使用外部库,我建议您查看Apache Commons库中的org.apache.commons.lang.StringUtils类.

用法示例:

List<String> list = Arrays.asList("Bill", "Bob", "Steve");
String joinedResult = StringUtils.join(list, " and ");

Answer 10

实现它的一种正统方法是定义一个新函数:

public static String join(String joinStr, String... strings) {
    if (strings == null || strings.length == 0) {
        return "";
    } else if (strings.length == 1) {
        return strings[0];
    } else {
        StringBuilder sb = new StringBuilder(strings.length * 1 + strings[0].length());
        sb.append(strings[0]);
        for (int i = 1; i < strings.length; i++) {
            sb.append(joinStr).append(strings[i]);
        }
        return sb.toString();
    }
}

样品:

String[] array = new String[] { "7, 7, 7", "Bill", "Bob", "Steve",
        "[Bill]", "1,2,3", "Apple ][","~,~" };

String joined;
joined = join(" and ","7, 7, 7", "Bill", "Bob", "Steve", "[Bill]", "1,2,3", "Apple ][","~,~");
joined = join(" and ", array); // same result

System.out.println(joined);

输出:

7,7,7和Bill和Bob和Steve以及[Bill]和1,2,3和Apple] [和〜,〜

Answer 11

您可以使用具有StringUtils类和join方法的apache commons库.

查看以下链接:https://commons.apache.org/proper/commons-lang/javadocs/api.2.0/org/apache/commons/lang/StringUtils.html

请注意,上面的链接可能会随着时间的推移而过时,在这种情况下,您只需在Web上搜索"apache commons StringUtils",这将允许您查找最新的引用.

(从这个线程引用) C#String.Format()和String.Join()的Java等价物

Answer 12

Java 8解决方案 java.util.StringJoiner

Java 8有一个StringJoiner类.但是你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);

Answer 13

你可以这样做:

String aToString = java.util.Arrays.toString(anArray);
// Do not need to do this if you are OK with '[' and ']'
aToString = aToString.substring(1, aToString.length() - 1);

或者单行(只有当你不想要'['和']'时)

String aToString = java.util.Arrays.toString(anArray).substring(1).replaceAll("\\]$", "");

希望这可以帮助.

Answer 14

与java 1.8流可以使用，

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

List<String> list = Arrays.asList("Bill","Bob","Steve").
String str = list.stream().collect(Collectors.joining(" and "));

Answer 15

一个有用的方法是使用纯JDK在一个职责范围内完成它:

String[] array = new String[] { "Bill", "Bob", "Steve","[Bill]","1,2,3","Apple ][" };
String join = " and ";

String joined = Arrays.toString(array).replaceAll(", ", join)
        .replaceAll("(^\\[)|(\\]$)", "");

System.out.println(joined);

输出:

比尔和鲍勃,史蒂夫和[比尔]和1,2,3和苹果] [

一个不太完美,不太有趣的方式!

String[] array = new String[] { "7, 7, 7","Bill", "Bob", "Steve", "[Bill]",
        "1,2,3", "Apple ][" };
String join = " and ";

for (int i = 0; i < array.length; i++) array[i] = array[i].replaceAll(", ", "~,~");
String joined = Arrays.toString(array).replaceAll(", ", join)
        .replaceAll("(^\\[)|(\\]$)", "").replaceAll("~,~", ", ");

System.out.println(joined);

输出:

7,7,7和Bill和Bob和Steve以及[Bill]和1,2,3和Apple] [