Package org.apache.commons.lang.text

Class StrSubstitutor

  • public class StrSubstitutor
extends Object
    Substitutes variables within a string by values.

    This class takes a piece of text and substitutes all the variables within it. The default definition of a variable is ${variableName}. The prefix and suffix can be changed via constructors and set methods.

    Variable values are typically resolved from a map, but could also be resolved from system properties, or by supplying a custom variable resolver.

    The simplest example is to use this class to replace Java System properties. For example: 

     StrSubstitutor.replaceSystemProperties(
      "You are running with java.version = ${java.version} and os.name = ${os.name}.");

    Typical usage of this class follows the following pattern: First an instance is created and initialized with the map that contains the values for the available variables. If a prefix and/or suffix for variables should be used other than the default ones, the appropriate settings can be performed. After that the replace() method can be called passing in the source text for interpolation. In the returned text all variable references (as long as their values are known) will be resolved. The following example demonstrates this: 

     Map valuesMap = HashMap();
 valuesMap.put("animal", "quick brown fox");
 valuesMap.put("target", "lazy dog");
 String templateString = "The ${animal} jumped over the ${target}.";
 StrSubstitutor sub = new StrSubstitutor(valuesMap);
 String resolvedString = sub.replace(templateString);
    yielding: 
          The quick brown fox jumped over the lazy dog.

    In addition to this usage pattern there are some static convenience methods that cover the most common use cases. These methods can be used without the need of manually creating an instance. However if multiple replace operations are to be performed, creating and reusing an instance of this class will be more efficient.

    Variable replacement works in a recursive way. Thus, if a variable value contains a variable then that variable will also be replaced. Cyclic replacements are detected and will cause an exception to be thrown.

    Sometimes the interpolation's result must contain a variable prefix. As an example take the following source text: 

       The variable ${${name}} must be used.
    Here only the variable's name referred to in the text should be replaced resulting in the text (assuming that the value of the name variable is x): 
       The variable ${x} must be used.
    To achieve this effect there are two possibilities: Either set a different prefix and suffix for variables which do not conflict with the result text you want to produce. The other possibility is to use the escape character, by default '$'. If this character is placed before a variable reference, this reference is ignored and won't be replaced. For example: 
       The variable $${${name}} must be used.

    In some complex scenarios you might even want to perform substitution in the names of variables, for instance 

     ${jre-${java.specification.version}}
    StrSubstitutor supports this recursive substitution in variable names, but it has to be enabled explicitly by setting the enableSubstitutionInVariables property to true.
    Since:
    2.2
    Version:
    $Id: StrSubstitutor.java 1057354 2011-01-10 20:48:47Z niallp $

    • Field Detail

      • DEFAULT_ESCAPE

        public static final char DEFAULT_ESCAPE
        Constant for the default escape character.
        See Also:
        Constant Field Values

      • DEFAULT_PREFIX

        public static final StrMatcher DEFAULT_PREFIX
        Constant for the default variable prefix.

      • DEFAULT_SUFFIX

        public static final StrMatcher DEFAULT_SUFFIX
        Constant for the default variable suffix.

    • Constructor Detail

      • StrSubstitutor

        public StrSubstitutor()
        Creates a new instance with defaults for variable prefix and suffix and the escaping character.

      • StrSubstitutor

        public StrSubstitutor​(Map valueMap)
        Creates a new instance and initializes it. Uses defaults for variable prefix and suffix and the escaping character.
        Parameters:
        valueMap - the map with the variables' values, may be null

      • StrSubstitutor

        public StrSubstitutor​(Map valueMap,
                      String prefix,
                      String suffix)
        Creates a new instance and initializes it. Uses a default escaping character.
        Parameters:
        valueMap - the map with the variables' values, may be null
        prefix - the prefix for variables, not null
        suffix - the suffix for variables, not null
        Throws:
        IllegalArgumentException - if the prefix or suffix is null

      • StrSubstitutor

        public StrSubstitutor​(Map valueMap,
                      String prefix,
                      String suffix,
                      char escape)
        Creates a new instance and initializes it.
        Parameters:
        valueMap - the map with the variables' values, may be null
        prefix - the prefix for variables, not null
        suffix - the suffix for variables, not null
        escape - the escape character
        Throws:
        IllegalArgumentException - if the prefix or suffix is null

      • StrSubstitutor

        public StrSubstitutor​(StrLookup variableResolver)
        Creates a new instance and initializes it.
        Parameters:
        variableResolver - the variable resolver, may be null

      • StrSubstitutor

        public StrSubstitutor​(StrLookup variableResolver,
                      String prefix,
                      String suffix,
                      char escape)
        Creates a new instance and initializes it.
        Parameters:
        variableResolver - the variable resolver, may be null
        prefix - the prefix for variables, not null
        suffix - the suffix for variables, not null
        escape - the escape character
        Throws:
        IllegalArgumentException - if the prefix or suffix is null

      • StrSubstitutor

        public StrSubstitutor​(StrLookup variableResolver,
                      StrMatcher prefixMatcher,
                      StrMatcher suffixMatcher,
                      char escape)
        Creates a new instance and initializes it.
        Parameters:
        variableResolver - the variable resolver, may be null
        prefixMatcher - the prefix for variables, not null
        suffixMatcher - the suffix for variables, not null
        escape - the escape character
        Throws:
        IllegalArgumentException - if the prefix or suffix is null

    • Method Detail

      • replace

        public static String replace​(Object source,
                             Map valueMap)
        Replaces all the occurrences of variables in the given source object with their matching values from the map.
        Parameters:
        source - the source text containing the variables to substitute, null returns null
        valueMap - the map with the values, may be null
        Returns:
        the result of the replace operation

      • replace

        public static String replace​(Object source,
                             Map valueMap,
                             String prefix,
                             String suffix)
        Replaces all the occurrences of variables in the given source object with their matching values from the map. This method allows to specifiy a custom variable prefix and suffix
        Parameters:
        source - the source text containing the variables to substitute, null returns null
        valueMap - the map with the values, may be null
        prefix - the prefix of variables, not null
        suffix - the suffix of variables, not null
        Returns:
        the result of the replace operation
        Throws:
        IllegalArgumentException - if the prefix or suffix is null

      • replace

        public static String replace​(Object source,
                             Properties valueProperties)
        Replaces all the occurrences of variables in the given source object with their matching values from the properties.
        Parameters:
        source - the source text containing the variables to substitute, null returns null
        valueProperties - the properties with values, may be null
        Returns:
        the result of the replace operation
        Since:
        2.6

      • replaceSystemProperties

        public static String replaceSystemProperties​(Object source)
        Replaces all the occurrences of variables in the given source object with their matching values from the system properties.
        Parameters:
        source - the source text containing the variables to substitute, null returns null
        Returns:
        the result of the replace operation

      • replace

        public String replace​(String source)
        Replaces all the occurrences of variables with their matching values from the resolver using the given source string as a template.
        Parameters:
        source - the string to replace in, null returns null
        Returns:
        the result of the replace operation

      • replace

        public String replace​(String source,
                      int offset,
                      int length)
        Replaces all the occurrences of variables with their matching values from the resolver using the given source string as a template.

        Only the specified portion of the string will be processed. The rest of the string is not processed, and is not returned.

        Parameters:
        source - the string to replace in, null returns null
        offset - the start offset within the array, must be valid
        length - the length within the array to be processed, must be valid
        Returns:
        the result of the replace operation

      • replace

        public String replace​(char[] source)
        Replaces all the occurrences of variables with their matching values from the resolver using the given source array as a template. The array is not altered by this method.
        Parameters:
        source - the character array to replace in, not altered, null returns null
        Returns:
        the result of the replace operation

      • replace

        public String replace​(char[] source,
                      int offset,
                      int length)
        Replaces all the occurrences of variables with their matching values from the resolver using the given source array as a template. The array is not altered by this method.

        Only the specified portion of the array will be processed. The rest of the array is not processed, and is not returned.

        Parameters:
        source - the character array to replace in, not altered, null returns null
        offset - the start offset within the array, must be valid
        length - the length within the array to be processed, must be valid
        Returns:
        the result of the replace operation

      • replace

        public String replace​(StringBuffer source)
        Replaces all the occurrences of variables with their matching values from the resolver using the given source buffer as a template. The buffer is not altered by this method.
        Parameters:
        source - the buffer to use as a template, not changed, null returns null
        Returns:
        the result of the replace operation

      • replace

        public String replace​(StringBuffer source,
                      int offset,
                      int length)
        Replaces all the occurrences of variables with their matching values from the resolver using the given source buffer as a template. The buffer is not altered by this method.

        Only the specified portion of the buffer will be processed. The rest of the buffer is not processed, and is not returned.

        Parameters:
        source - the buffer to use as a template, not changed, null returns null
        offset - the start offset within the array, must be valid
        length - the length within the array to be processed, must be valid
        Returns:
        the result of the replace operation

      • replace

        public String replace​(StrBuilder source)
        Replaces all the occurrences of variables with their matching values from the resolver using the given source builder as a template. The builder is not altered by this method.
        Parameters:
        source - the builder to use as a template, not changed, null returns null
        Returns:
        the result of the replace operation

      • replace

        public String replace​(StrBuilder source,
                      int offset,
                      int length)
        Replaces all the occurrences of variables with their matching values from the resolver using the given source builder as a template. The builder is not altered by this method.

        Only the specified portion of the builder will be processed. The rest of the builder is not processed, and is not returned.

        Parameters:
        source - the builder to use as a template, not changed, null returns null
        offset - the start offset within the array, must be valid
        length - the length within the array to be processed, must be valid
        Returns:
        the result of the replace operation

      • replace

        public String replace​(Object source)
        Replaces all the occurrences of variables in the given source object with their matching values from the resolver. The input source object is converted to a string using toString and is not altered.
        Parameters:
        source - the source to replace in, null returns null
        Returns:
        the result of the replace operation

      • replaceIn

        public boolean replaceIn​(StringBuffer source)
        Replaces all the occurrences of variables within the given source buffer with their matching values from the resolver. The buffer is updated with the result.
        Parameters:
        source - the buffer to replace in, updated, null returns zero
        Returns:
        true if altered

      • replaceIn

        public boolean replaceIn​(StringBuffer source,
                         int offset,
                         int length)
        Replaces all the occurrences of variables within the given source buffer with their matching values from the resolver. The buffer is updated with the result.

        Only the specified portion of the buffer will be processed. The rest of the buffer is not processed, but it is not deleted.

        Parameters:
        source - the buffer to replace in, updated, null returns zero
        offset - the start offset within the array, must be valid
        length - the length within the buffer to be processed, must be valid
        Returns:
        true if altered

      • replaceIn

        public boolean replaceIn​(StrBuilder source)
        Replaces all the occurrences of variables within the given source builder with their matching values from the resolver.
        Parameters:
        source - the builder to replace in, updated, null returns zero
        Returns:
        true if altered

      • replaceIn

        public boolean replaceIn​(StrBuilder source,
                         int offset,
                         int length)
        Replaces all the occurrences of variables within the given source builder with their matching values from the resolver.

        Only the specified portion of the builder will be processed. The rest of the builder is not processed, but it is not deleted.

        Parameters:
        source - the builder to replace in, null returns zero
        offset - the start offset within the array, must be valid
        length - the length within the builder to be processed, must be valid
        Returns:
        true if altered

      • substitute

        protected boolean substitute​(StrBuilder buf,
                             int offset,
                             int length)
        Internal method that substitutes the variables.

        Most users of this class do not need to call this method. This method will be called automatically by another (public) method.

        Writers of subclasses can override this method if they need access to the substitution process at the start or end.

        Parameters:
        buf - the string builder to substitute into, not null
        offset - the start offset within the builder, must be valid
        length - the length within the builder to be processed, must be valid
        Returns:
        true if altered

      • resolveVariable

        protected String resolveVariable​(String variableName,
                                 StrBuilder buf,
                                 int startPos,
                                 int endPos)
        Internal method that resolves the value of a variable.

        Most users of this class do not need to call this method. This method is called automatically by the substitution process.

        Writers of subclasses can override this method if they need to alter how each substitution occurs. The method is passed the variable's name and must return the corresponding value. This implementation uses the getVariableResolver() with the variable's name as the key.

        Parameters:
        variableName - the name of the variable, not null
        buf - the buffer where the substitution is occurring, not null
        startPos - the start position of the variable including the prefix, valid
        endPos - the end position of the variable including the suffix, valid
        Returns:
        the variable's value or null if the variable is unknown

      • getEscapeChar

        public char getEscapeChar()
        Returns the escape character.
        Returns:
        the character used for escaping variable references

      • setEscapeChar

        public void setEscapeChar​(char escapeCharacter)
        Sets the escape character. If this character is placed before a variable reference in the source text, this variable will be ignored.
        Parameters:
        escapeCharacter - the escape character (0 for disabling escaping)

      • getVariablePrefixMatcher

        public StrMatcher getVariablePrefixMatcher()
        Gets the variable prefix matcher currently in use.

        The variable prefix is the characer or characters that identify the start of a variable. This prefix is expressed in terms of a matcher allowing advanced prefix matches.

        Returns:
        the prefix matcher in use

      • setVariablePrefixMatcher

        public StrSubstitutor setVariablePrefixMatcher​(StrMatcher prefixMatcher)
        Sets the variable prefix matcher currently in use.

        The variable prefix is the characer or characters that identify the start of a variable. This prefix is expressed in terms of a matcher allowing advanced prefix matches.

        Parameters:
        prefixMatcher - the prefix matcher to use, null ignored
        Returns:
        this, to enable chaining
        Throws:
        IllegalArgumentException - if the prefix matcher is null

      • setVariablePrefix

        public StrSubstitutor setVariablePrefix​(char prefix)
        Sets the variable prefix to use.

        The variable prefix is the character or characters that identify the start of a variable. This method allows a single character prefix to be easily set.

        Parameters:
        prefix - the prefix character to use
        Returns:
        this, to enable chaining

      • setVariablePrefix

        public StrSubstitutor setVariablePrefix​(String prefix)
        Sets the variable prefix to use.

        The variable prefix is the characer or characters that identify the start of a variable. This method allows a string prefix to be easily set.

        Parameters:
        prefix - the prefix for variables, not null
        Returns:
        this, to enable chaining
        Throws:
        IllegalArgumentException - if the prefix is null

      • getVariableSuffixMatcher

        public StrMatcher getVariableSuffixMatcher()
        Gets the variable suffix matcher currently in use.

        The variable suffix is the characer or characters that identify the end of a variable. This suffix is expressed in terms of a matcher allowing advanced suffix matches.

        Returns:
        the suffix matcher in use

      • setVariableSuffixMatcher

        public StrSubstitutor setVariableSuffixMatcher​(StrMatcher suffixMatcher)
        Sets the variable suffix matcher currently in use.

        The variable suffix is the characer or characters that identify the end of a variable. This suffix is expressed in terms of a matcher allowing advanced suffix matches.

        Parameters:
        suffixMatcher - the suffix matcher to use, null ignored
        Returns:
        this, to enable chaining
        Throws:
        IllegalArgumentException - if the suffix matcher is null

      • setVariableSuffix

        public StrSubstitutor setVariableSuffix​(char suffix)
        Sets the variable suffix to use.

        The variable suffix is the characer or characters that identify the end of a variable. This method allows a single character suffix to be easily set.

        Parameters:
        suffix - the suffix character to use
        Returns:
        this, to enable chaining

      • setVariableSuffix

        public StrSubstitutor setVariableSuffix​(String suffix)
        Sets the variable suffix to use.

        The variable suffix is the character or characters that identify the end of a variable. This method allows a string suffix to be easily set.

        Parameters:
        suffix - the suffix for variables, not null
        Returns:
        this, to enable chaining
        Throws:
        IllegalArgumentException - if the suffix is null

      • getVariableResolver

        public StrLookup getVariableResolver()
        Gets the VariableResolver that is used to lookup variables.
        Returns:
        the VariableResolver

      • setVariableResolver

        public void setVariableResolver​(StrLookup variableResolver)
        Sets the VariableResolver that is used to lookup variables.
        Parameters:
        variableResolver - the VariableResolver

      • isEnableSubstitutionInVariables

        public boolean isEnableSubstitutionInVariables()
        Returns a flag whether substitution is done in variable names.
        Returns:
        the substitution in variable names flag
        Since:
        2.6

      • setEnableSubstitutionInVariables

        public void setEnableSubstitutionInVariables​(boolean enableSubstitutionInVariables)
        Sets a flag whether substitution is done in variable names. If set to true, the names of variables can contain other variables which are processed first before the original variable is evaluated, e.g. ${jre-${java.version}}. The default value is false.
        Parameters:
        enableSubstitutionInVariables - the new value of the flag
        Since:
        2.6