如何简化 java 中的 String concat?

How to simplify String concat in java?

给定以下代码:

private static final String DELIMITER = " ";

  @AfterMapping
  protected void createCompactInfo(@MappingTarget User user) {
    String vorname = Optional.ofNullable(user.getVorname()).orElse(Strings.EMPTY);
    String nachname = Optional.ofNullable(user.getNachname()).orElse(Strings.EMPTY);
    String email = Optional.ofNullable(user.getEmail()).orElse(Strings.EMPTY);
    String compactInfo =
        (vorname
                + DELIMITER
                + nachname
                + DELIMITER
                + (email.isEmpty() ? Strings.EMPTY : "(" + email + ")"))
            .trim();
    if (compactInfo.isEmpty()) {
      user.setCompakt(
          Optional.ofNullable(user.getId()).orElse(Strings.EMPTY));
    } else {
      user.setCompakt(compactInfo);
    }

我正在团队中尝试和讨论最简单的代码看起来如何,同时也可以使用如下结构:

一个可能的测试可能是这样的(预期结果也在这里可见):

private static Stream<Arguments> arguments() {
    return Stream.of(
        Arguments.of("Peter", "Silie", "peter@silie.org", "BOND", "Peter Silie (peter@silie.org)"),
        Arguments.of(null, "Silie", "peter@silie.org", "BOND", "Silie (peter@silie.org)"),
        Arguments.of("Peter", null, "peter@silie.org", "BOND", "Peter (peter@silie.org)"),
        Arguments.of("Peter", "Silie", null, "BOND", "Peter Silie"),
        Arguments.of(null, "Silie", null, "BOND", "Silie"),
        Arguments.of(null, null, "peter@silie.org", "BOND", "(peter@silie.org)"),
        Arguments.of("Peter", null, null, "BOND", "Peter"),
        Arguments.of(null, null, null, "BOND", "BOND"));
  }

  @ParameterizedTest(
      name = "{index}" + ". Test: vorname={0}, nachname={1}, email={2}; expected: {3}")
  @MethodSource(value = "arguments")
  void verifyUserKompakt(
      String vorname, String nachname, String email, String kuerzel, String expectedResult) {

    // arrange
    Base base =
        Base.builder()
            .vorname(vorname)
            .nachname(nachname)
            .email(email)
            .kuerzel(kuerzel)
            .build();

    // act
    User userResult =
        userMapperImpl.doIt(base);

    // assert
    assertThat(userResult.getUserKompakt()).isEqualTo(expectedResult);
  }

欢迎提出任何想法...我可以尝试什么?

顺便说一句:java 17 是允许的:-)

以下代码似乎非常接近,但不处理电子邮件的大括号(如果存在):

String compactInfo =
        (Stream.of(
                    user.getVorname(),
                    user.getNachname(),
                    user.getEmail())
                .map(s -> s != null ? s : "")
                .collect(Collectors.joining(" ")))
            .trim();

    user.setUserKompakt(
        compactInfo.isEmpty()
            ? Optional.ofNullable(user.getKuerzel()).orElse("")
            : compactInfo);

由于您有重复的代码来转换 vornamenachnameuserId,您可能希望将逻辑提取到 Function or an UnaryOperator,因为它是一个字符串到字符串转换和电子邮件的附加转换。例子

import java.util.function.UnaryOperator;

....

private static final String EMPTY = "";
private static final String DELIMITER = " ";

UnaryOperator<String> nameOp = o -> Optional.ofNullable(o).orElse(EMPTY);
UnaryOperator<String> mailOp = o -> Optional.ofNullable(o).map(s -> String.format("(%s)", s)).orElse(EMPTY);

@AfterMapping
protected void createCompactInfo(@MappingTarget User user) {
   String compactInfo = Stream.of(nameOp.apply(user.getVorname()),
                                  nameOp.apply(user.getNachname()),
                                  mailOp.apply(user.getEmail()))
                               .filter(Predicate.not(String::isEmpty))
                               .collect(Collectors.joining(DELIMITER));

   user.setCompakt(compactInfo.isEmpty() ? nameOp.apply(user.getId()) : compactInfo);
}

Java 普通连接和 StringBuilder/StringBuffer 之间存在巨大的性能差异。

在进行字符串连接时观察您的方法 createCompactInfo: compactInfo = ... 将导致性能不佳。

我建议您尝试使用 StringBuilder 或 StringBuffer。

字符串是不可变对象,这意味着值无法更改,因此每次执行串联 strA + strB 都会产生一个新对象。

比较普通连接与 StringBuilder 的性能结果:

public class ConcatenateString {
    public static void main (String[] args){
          String strFinal = "";
          long tStart = System.currentTimeMillis();
          for(int i = 0; i < 100000; i ++){
                 strFinal += "a";
          }
          long tEnd = System.currentTimeMillis();
          long tResult = tEnd - tStart;
          System.out.println("Runtime with operator + = "+tResult+" ms");

     
          StringBuilder strBuilder = new StringBuilder();
          tStart = System.currentTimeMillis();
          for(int i = 0; i < 100000; i ++){
                 strBuilder.append("a");
          }
          tEnd = System.currentTimeMillis();
          tResult = tEnd - tStart;
          System.out.println("Runtime with StringBuilder= "+tResult+" ms");
    }
}

结果(位于:Darwin Macs-iMac Darwin 内核版本 20.6.0:8 月 30 日星期一 06:12:21 PDT 2021;RELEASE_X86_64 x86_64 - Intel I5 处理器 2.5ghz):

Runtime with operator + = 1469 ms
Runtime with StringBuilder= 2 ms