Class DefaultListDelimiterHandler

All Implemented Interfaces:

The default implementation of the ListDelimiterHandler interface.

This class supports list splitting and delimiter escaping using a delimiter character that can be specified when constructing an instance. Splitting of strings works by scanning the input for the list delimiter character. The list delimiter character can be escaped by a backslash. So, provided that a comma is configured as list delimiter, in the example val1,val2,val3 three values are recognized. In 3\,1415 the list delimiter is escaped so that only a single element is detected. (Note that when writing these examples in Java code, each backslash has to be doubled. This is also true for all other examples in this documentation.)

Because the backslash has a special meaning as escaping character it is always treated in a special way. If it occurs as a normal character in a property value, it has to be escaped using another backslash (similar to the rules of the Java programming language). The following example shows the correct way to define windows network shares: \\\\Server\\path. Note that each backslash is doubled. When combining the list delimiter with backslashes the same escaping rules apply. For instance, in C:\\Temp\\,D:\\data\\ the list delimiter is recognized; it is not escaped by the preceding backslash because this backslash is itself escaped. In contrast, C:\\Temp\\\,D:\\data\\ defines a single element with a comma being part of the value; two backslashes after Temp result in a single one, the third backslash escapes the list delimiter.

As can be seen, there are some constellations which are a bit tricky and cause a larger number of backslashes in sequence. Nevertheless, the escaping rules are consistent and do not cause ambiguous results.

Implementation node: An instance of this class can safely be shared between multiple Configuration instances.

  • Constructor Details

    • DefaultListDelimiterHandler

      public DefaultListDelimiterHandler(char listDelimiter)
      Creates a new instance of DefaultListDelimiterHandler and sets the list delimiter character.
      listDelimiter - the list delimiter character
  • Method Details

    • getDelimiter

      public char getDelimiter()
      Gets the list delimiter character used by this instance.
      the list delimiter character
    • escapeList

      public Object escapeList(List<?> values, ValueTransformer transformer)
      Description copied from interface: ListDelimiterHandler
      Escapes all values in the given list and concatenates them to a single string. This operation is required by configurations that have to represent properties with multiple values in a single line in their external configuration representation. This may require an advanced escaping in some cases.
      values - the list with all the values to be converted to a single value
      transformer - a ValueTransformer for an additional encoding (must not be null)
      the resulting escaped value
    • escapeString

      protected String escapeString(String s)
      Description copied from class: AbstractListDelimiterHandler
      Escapes the specified string. This method is called by escape() if the passed in object is a string. Concrete subclasses have to implement their specific escaping logic here, so that the list delimiters they support are properly escaped.
      Specified by:
      escapeString in class AbstractListDelimiterHandler
      s - the string to be escaped (not null)
      the escaped string
    • splitString

      protected Collection<String> splitString(String s, boolean trim)
      Actually splits the passed in string which is guaranteed to be not null. This method is called by the base implementation of the split() method. Here the actual splitting logic has to be implemented. This implementation reverses the escaping done by the escape() methods of this class. However, it tries to be tolerant with unexpected escaping sequences: If after the escape character "\" no allowed character follows, both the backslash and the following character are output.
      Specified by:
      splitString in class AbstractListDelimiterHandler
      s - the string to be split (not null)
      trim - a flag whether the single components have to be trimmed
      a collection with the extracted components of the passed in string