在Java中自动椭圆化字符串 [英] Automatically ellipsize a string in Java

问题描述

Java中有一种自动椭圆化字符串的方法吗？只是在Java中，而不是其他库。

Is there a method in Java to automatically ellipsize a string? Just in Java, not other libraries.

谢谢。

推荐答案

根据您的使用情况，将省略号放在字母之间（即在末尾添加字母以提供一些上下文）可能很有用：

Depending on your use case, it might be useful to put the ellipsis between letters (i.e. add letters at the end to provide some context):

/**
 * Puts ellipses in input strings that are longer than than maxCharacters. Shorter strings or
 * null is returned unchanged.
 * @param input the input string that may be subjected to shortening
 * @param maxCharacters the maximum characters that are acceptable for the unshortended string. Must be at least 3, otherwise a string with ellipses is too long already.
 * @param charactersAfterEllipsis the number of characters that should appear after the ellipsis (0 or larger) 
 * @return the truncated string with trailing ellipses
 */
public static String ellipsize(String input, int maxCharacters, int charactersAfterEllipsis) {
  if(maxCharacters < 3) {
    throw new IllegalArgumentException("maxCharacters must be at least 3 because the ellipsis already take up 3 characters");
  }
  if(maxCharacters - 3 > charactersAfterEllipsis) {
    throw new IllegalArgumentException("charactersAfterEllipsis must be less than maxCharacters");
  }
  if (input == null || input.length() < maxCharacters) {
    return input;
  }
  return input.substring(0, maxCharacters - 3 - charactersAfterEllipsis) + "..." + input.substring(input.length() - charactersAfterEllipsis);
}

您还可以从省略号算法中获得更复杂的功能：如果您需要将文本放入图形元素并使用比例字体，然后必须测量字符串的长度。

There are also more sophisticated features you might want from you ellipsis algorithm: If you need to place the text into a graphical element and you are using a proportional font, then you must measure the length of the String.

对于Swing / AWT将是 java.awt.Font.getStringBounds 。在这种情况下，一个简单的algrithm会一次一个字母地剪切字符串并添加省略号，直到字符串符合给定的限制。如果经常使用，则在 http：//www.codeproject中详细阐述了二分法。 .com / KB / cs / AutoEllipsis.aspx？msg = 3278640 （C＃，但应该很容易转换为Java）可以节省一些处理器周期。

For Swing/AWT that would be java.awt.Font.getStringBounds. In such a case, a simple algrithm would cut the string one letter at a time and add the ellipsis, until the string fits into the limit given. If used often, the bisection method elaborated in http://www.codeproject.com/KB/cs/AutoEllipsis.aspx?msg=3278640 (C#, but should be easy enough to translate to Java) may save some processor cycles.

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