Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.lang.text; import java.util.ArrayList; import java.util.List; import java.util.Map; /** * Substitutes variables within a string by values. * <p> * This class takes a piece of text and substitutes all the variables within it. * The default definition of a variable is <code>${variableName}</code>. * The prefix and suffix can be changed via constructors and set methods. * <p> * Variable values are typically resolved from a map, but could also be resolved * from system properties, or by supplying a custom variable resolver. * <p> * The simplest example is to use this class to replace Java System properties. For example: * <pre> * StrSubstitutor.replaceSystemProperties( * "You are running with java.version = ${java.version} and os.name = ${os.name}."); * </pre> * <p> * 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 <code>replace()</code> * 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: * <pre> * 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); * </pre> * yielding: * <pre> * The quick brown fox jumped over the lazy dog. * </pre> * <p> * 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. * <p> * 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. * <p> * Sometimes the interpolation's result must contain a variable prefix. As an example * take the following source text: * <pre> * The variable ${${name}} must be used. * </pre> * Here only the variable's name refered to in the text should be replaced resulting * in the text (assuming that the value of the <code>name</code> variable is <code>x</code>): * <pre> * The variable ${x} must be used. * </pre> * To achieve this effect there are two possibilities: Either set a different prefix * and suffix for variables which do not conflict with the result text you want to * produce. The other possibility is to use the escape character, by default '$'. * If this character is placed before a variable reference, this reference is ignored * and won't be replaced. For example: * <pre> * The variable $${${name}} must be used. * </pre> * * @author Oliver Heger * @author Stephen Colebourne * @version $Id: StrSubstitutor.java 437554 2006-08-28 06:21:41Z bayard $ * @since 2.2 */ public class StrSubstitutor { /** * Constant for the default escape character. */ public static final char DEFAULT_ESCAPE = '$'; /** * Constant for the default variable prefix. */ public static final StrMatcher DEFAULT_PREFIX = StrMatcher.stringMatcher("${"); /** * Constant for the default variable suffix. */ public static final StrMatcher DEFAULT_SUFFIX = StrMatcher.stringMatcher("}"); /** * Stores the escape character. */ private char escapeChar; /** * Stores the variable prefix. */ private StrMatcher prefixMatcher; /** * Stores the variable suffix. */ private StrMatcher suffixMatcher; /** * Variable resolution is delegated to an implementor of VariableResolver. */ private StrLookup variableResolver; //----------------------------------------------------------------------- /** * Replaces all the occurrences of variables in the given source object with * their matching values from the map. * * @param source the source text containing the variables to substitute, null returns null * @param valueMap the map with the values, may be null * @return the result of the replace operation */ public static String replace(Object source, Map valueMap) { return new StrSubstitutor(valueMap).replace(source); } /** * 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 * * @param source the source text containing the variables to substitute, null returns null * @param valueMap the map with the values, may be null * @param prefix the prefix of variables, not null * @param suffix the suffix of variables, not null * @return the result of the replace operation * @throws IllegalArgumentException if the prefix or suffix is null */ public static String replace(Object source, Map valueMap, String prefix, String suffix) { return new StrSubstitutor(valueMap, prefix, suffix).replace(source); } /** * Replaces all the occurrences of variables in the given source object with * their matching values from the system properties. * * @param source the source text containing the variables to substitute, null returns null * @return the result of the replace operation */ public static String replaceSystemProperties(Object source) { return new StrSubstitutor(StrLookup.systemPropertiesLookup()).replace(source); } //----------------------------------------------------------------------- /** * Creates a new instance with defaults for variable prefix and suffix * and the escaping character. */ public StrSubstitutor() { this((StrLookup) null, DEFAULT_PREFIX, DEFAULT_SUFFIX, DEFAULT_ESCAPE); } /** * Creates a new instance and initializes it. Uses defaults for variable * prefix and suffix and the escaping character. * * @param valueMap the map with the variables' values, may be null */ public StrSubstitutor(Map valueMap) { this(StrLookup.mapLookup(valueMap), DEFAULT_PREFIX, DEFAULT_SUFFIX, DEFAULT_ESCAPE); } /** * Creates a new instance and initializes it. Uses a default escaping character. * * @param valueMap the map with the variables' values, may be null * @param prefix the prefix for variables, not null * @param suffix the suffix for variables, not null * @throws IllegalArgumentException if the prefix or suffix is null */ public StrSubstitutor(Map valueMap, String prefix, String suffix) { this(StrLookup.mapLookup(valueMap), prefix, suffix, DEFAULT_ESCAPE); } /** * Creates a new instance and initializes it. * * @param valueMap the map with the variables' values, may be null * @param prefix the prefix for variables, not null * @param suffix the suffix for variables, not null * @param escape the escape character * @throws IllegalArgumentException if the prefix or suffix is null */ public StrSubstitutor(Map valueMap, String prefix, String suffix, char escape) { this(StrLookup.mapLookup(valueMap), prefix, suffix, escape); } /** * Creates a new instance and initializes it. * * @param variableResolver the variable resolver, may be null */ public StrSubstitutor(StrLookup variableResolver) { this(variableResolver, DEFAULT_PREFIX, DEFAULT_SUFFIX, DEFAULT_ESCAPE); } /** * Creates a new instance and initializes it. * * @param variableResolver the variable resolver, may be null * @param prefix the prefix for variables, not null * @param suffix the suffix for variables, not null * @param escape the escape character * @throws IllegalArgumentException if the prefix or suffix is null */ public StrSubstitutor(StrLookup variableResolver, String prefix, String suffix, char escape) { this.setVariableResolver(variableResolver); this.setVariablePrefix(prefix); this.setVariableSuffix(suffix); this.setEscapeChar(escape); } /** * Creates a new instance and initializes it. * * @param variableResolver the variable resolver, may be null * @param prefixMatcher the prefix for variables, not null * @param suffixMatcher the suffix for variables, not null * @param escape the escape character * @throws IllegalArgumentException if the prefix or suffix is null */ public StrSubstitutor(StrLookup variableResolver, StrMatcher prefixMatcher, StrMatcher suffixMatcher, char escape) { this.setVariableResolver(variableResolver); this.setVariablePrefixMatcher(prefixMatcher); this.setVariableSuffixMatcher(suffixMatcher); this.setEscapeChar(escape); } //----------------------------------------------------------------------- /** * Replaces all the occurrences of variables with their matching values * from the resolver using the given source string as a template. * * @param source the string to replace in, null returns null * @return the result of the replace operation */ public String replace(String source) { if (source == null) { return null; } StrBuilder buf = new StrBuilder(source); if (substitute(buf, 0, source.length()) == false) { return source; } return buf.toString(); } /** * Replaces all the occurrences of variables with their matching values * from the resolver using the given source string as a template. * <p> * Only the specified portion of the string will be processed. * The rest of the string is not processed, and is not returned. * * @param source the string to replace in, null returns null * @param offset the start offset within the array, must be valid * @param length the length within the array to be processed, must be valid * @return the result of the replace operation */ public String replace(String source, int offset, int length) { if (source == null) { return null; } StrBuilder buf = new StrBuilder(length).append(source, offset, length); if (substitute(buf, 0, length) == false) { return source.substring(offset, offset + length); } return buf.toString(); } //----------------------------------------------------------------------- /** * 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. * * @param source the character array to replace in, not altered, null returns null * @return the result of the replace operation */ public String replace(char[] source) { if (source == null) { return null; } StrBuilder buf = new StrBuilder(source.length).append(source); substitute(buf, 0, source.length); return buf.toString(); } /** * 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. * <p> * Only the specified portion of the array will be processed. * The rest of the array is not processed, and is not returned. * * @param source the character array to replace in, not altered, null returns null * @param offset the start offset within the array, must be valid * @param length the length within the array to be processed, must be valid * @return the result of the replace operation */ public String replace(char[] source, int offset, int length) { if (source == null) { return null; } StrBuilder buf = new StrBuilder(length).append(source, offset, length); substitute(buf, 0, length); return buf.toString(); } //----------------------------------------------------------------------- /** * 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. * * @param source the buffer to use as a template, not changed, null returns null * @return the result of the replace operation */ public String replace(StringBuffer source) { if (source == null) { return null; } StrBuilder buf = new StrBuilder(source.length()).append(source); substitute(buf, 0, buf.length()); return buf.toString(); } /** * 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. * <p> * Only the specified portion of the buffer will be processed. * The rest of the buffer is not processed, and is not returned. * * @param source the buffer to use as a template, not changed, null returns null * @param offset the start offset within the array, must be valid * @param length the length within the array to be processed, must be valid * @return the result of the replace operation */ public String replace(StringBuffer source, int offset, int length) { if (source == null) { return null; } StrBuilder buf = new StrBuilder(length).append(source, offset, length); substitute(buf, 0, length); return buf.toString(); } //----------------------------------------------------------------------- /** * 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. * * @param source the builder to use as a template, not changed, null returns null * @return the result of the replace operation */ public String replace(StrBuilder source) { if (source == null) { return null; } StrBuilder buf = new StrBuilder(source.length()).append(source); substitute(buf, 0, buf.length()); return buf.toString(); } /** * 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. * <p> * Only the specified portion of the builder will be processed. * The rest of the builder is not processed, and is not returned. * * @param source the builder to use as a template, not changed, null returns null * @param offset the start offset within the array, must be valid * @param length the length within the array to be processed, must be valid * @return the result of the replace operation */ public String replace(StrBuilder source, int offset, int length) { if (source == null) { return null; } StrBuilder buf = new StrBuilder(length).append(source, offset, length); substitute(buf, 0, length); return buf.toString(); } //----------------------------------------------------------------------- /** * 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 <code>toString</code> and is not altered. * * @param source the source to replace in, null returns null * @return the result of the replace operation */ public String replace(Object source) { if (source == null) { return null; } StrBuilder buf = new StrBuilder().append(source); substitute(buf, 0, buf.length()); return buf.toString(); } //----------------------------------------------------------------------- /** * 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. * * @param source the buffer to replace in, updated, null returns zero * @return true if altered */ public boolean replaceIn(StringBuffer source) { if (source == null) { return false; } return replaceIn(source, 0, source.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. * <p> * Only the specified portion of the buffer will be processed. * The rest of the buffer is not processed, but it is not deleted. * * @param source the buffer to replace in, updated, null returns zero * @param offset the start offset within the array, must be valid * @param length the length within the buffer to be processed, must be valid * @return true if altered */ public boolean replaceIn(StringBuffer source, int offset, int length) { if (source == null) { return false; } StrBuilder buf = new StrBuilder(length).append(source, offset, length); if (substitute(buf, 0, length) == false) { return false; } source.replace(offset, offset + length, buf.toString()); return true; } //----------------------------------------------------------------------- /** * Replaces all the occurrences of variables within the given source * builder with their matching values from the resolver. * * @param source the builder to replace in, updated, null returns zero * @return true if altered */ public boolean replaceIn(StrBuilder source) { if (source == null) { return false; } return substitute(source, 0, source.length()); } /** * Replaces all the occurrences of variables within the given source * builder with their matching values from the resolver. * <p> * Only the specified portion of the builder will be processed. * The rest of the builder is not processed, but it is not deleted. * * @param source the builder to replace in, null returns zero * @param offset the start offset within the array, must be valid * @param length the length within the builder to be processed, must be valid * @return true if altered */ public boolean replaceIn(StrBuilder source, int offset, int length) { if (source == null) { return false; } return substitute(source, offset, length); } //----------------------------------------------------------------------- /** * Internal method that substitutes the variables. * <p> * Most users of this class do not need to call this method. This method will * be called automatically by another (public) method. * <p> * Writers of subclasses can override this method if they need access to * the substitution process at the start or end. * * @param buf the string builder to substitute into, not null * @param offset the start offset within the builder, must be valid * @param length the length within the builder to be processed, must be valid * @return true if altered */ protected boolean substitute(StrBuilder buf, int offset, int length) { return substitute(buf, offset, length, null) > 0; } /** * Recursive handler for multiple levels of interpolation. This is the main * interpolation method, which resolves the values of all variable references * contained in the passed in text. * * @param buf the string builder to substitute into, not null * @param offset the start offset within the builder, must be valid * @param length the length within the builder to be processed, must be valid * @param priorVariables the stack keeping track of the replaced variables, may be null * @return the length change that occurs, unless priorVariables is null when the int * represents a boolean flag as to whether any change occurred. */ private int substitute(StrBuilder buf, int offset, int length, List priorVariables) { StrMatcher prefixMatcher = getVariablePrefixMatcher(); StrMatcher suffixMatcher = getVariableSuffixMatcher(); char escape = getEscapeChar(); boolean top = (priorVariables == null); boolean altered = false; int lengthChange = 0; char[] chars = buf.buffer; int bufEnd = offset + length; int pos = offset; while (pos < bufEnd) { int startMatchLen = prefixMatcher.isMatch(chars, pos, offset, bufEnd); if (startMatchLen == 0) { pos++; } else { // found variable start marker if (pos > offset && chars[pos - 1] == escape) { // escaped buf.deleteCharAt(pos - 1); chars = buf.buffer; // in case buffer was altered lengthChange--; altered = true; bufEnd--; } else { // find suffix int startPos = pos; pos += startMatchLen; int endMatchLen = 0; while (pos < bufEnd) { endMatchLen = suffixMatcher.isMatch(chars, pos, offset, bufEnd); if (endMatchLen == 0) { pos++; } else { // found variable end marker String varName = new String(chars, startPos + startMatchLen, pos - startPos - startMatchLen); pos += endMatchLen; int endPos = pos; // on the first call initialize priorVariables if (priorVariables == null) { priorVariables = new ArrayList(); priorVariables.add(new String(chars, offset, length)); } // handle cyclic substitution checkCyclicSubstitution(varName, priorVariables); priorVariables.add(varName); // resolve the variable String varValue = resolveVariable(varName, buf, startPos, endPos); if (varValue != null) { // recursive replace int varLen = varValue.length(); buf.replace(startPos, endPos, varValue); altered = true; int change = substitute(buf, startPos, varLen, priorVariables); change = change + (varLen - (endPos - startPos)); pos += change; bufEnd += change; lengthChange += change; chars = buf.buffer; // in case buffer was altered } // remove variable from the cyclic stack priorVariables.remove(priorVariables.size() - 1); break; } } } } } if (top) { return (altered ? 1 : 0); } return lengthChange; } /** * Checks if the specified variable is already in the stack (list) of variables. * * @param varName the variable name to check * @param priorVariables the list of prior variables */ private void checkCyclicSubstitution(String varName, List priorVariables) { if (priorVariables.contains(varName) == false) { return; } StrBuilder buf = new StrBuilder(256); buf.append("Infinite loop in property interpolation of "); buf.append(priorVariables.remove(0)); buf.append(": "); buf.appendWithSeparators(priorVariables, "->"); throw new IllegalStateException(buf.toString()); } /** * Internal method that resolves the value of a variable. * <p> * Most users of this class do not need to call this method. This method is * called automatically by the substitution process. * <p> * 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 * {@link #getVariableResolver()} with the variable's name as the key. * * @param variableName the name of the variable, not null * @param buf the buffer where the substitution is occurring, not null * @param startPos the start position of the variable including the prefix, valid * @param endPos the end position of the variable including the suffix, valid * @return the variable's value or <b>null</b> if the variable is unknown */ protected String resolveVariable(String variableName, StrBuilder buf, int startPos, int endPos) { StrLookup resolver = getVariableResolver(); if (resolver == null) { return null; } return resolver.lookup(variableName); } // Escape //----------------------------------------------------------------------- /** * Returns the escape character. * * @return the character used for escaping variable references */ public char getEscapeChar() { return this.escapeChar; } /** * Sets the escape character. * If this character is placed before a variable reference in the source * text, this variable will be ignored. * * @param escapeCharacter the escape character (0 for disabling escaping) */ public void setEscapeChar(char escapeCharacter) { this.escapeChar = escapeCharacter; } // Prefix //----------------------------------------------------------------------- /** * Gets the variable prefix matcher currently in use. * <p> * 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. * * @return the prefix matcher in use */ public StrMatcher getVariablePrefixMatcher() { return prefixMatcher; } /** * Sets the variable prefix matcher currently in use. * <p> * 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. * * @param prefixMatcher the prefix matcher to use, null ignored * @return this, to enable chaining * @throws IllegalArgumentException if the prefix matcher is null */ public StrSubstitutor setVariablePrefixMatcher(StrMatcher prefixMatcher) { if (prefixMatcher == null) { throw new IllegalArgumentException("Variable prefix matcher must not be null!"); } this.prefixMatcher = prefixMatcher; return this; } /** * Sets the variable prefix to use. * <p> * The variable prefix is the characer or characters that identify the * start of a variable. This method allows a single character prefix to * be easily set. * * @param prefix the prefix character to use * @return this, to enable chaining */ public StrSubstitutor setVariablePrefix(char prefix) { return setVariablePrefixMatcher(StrMatcher.charMatcher(prefix)); } /** * Sets the variable prefix to use. * <p> * 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. * * @param prefix the prefix for variables, not null * @return this, to enable chaining * @throws IllegalArgumentException if the prefix is null */ public StrSubstitutor setVariablePrefix(String prefix) { if (prefix == null) { throw new IllegalArgumentException("Variable prefix must not be null!"); } return setVariablePrefixMatcher(StrMatcher.stringMatcher(prefix)); } // Suffix //----------------------------------------------------------------------- /** * Gets the variable suffix matcher currently in use. * <p> * 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. * * @return the suffix matcher in use */ public StrMatcher getVariableSuffixMatcher() { return suffixMatcher; } /** * Sets the variable suffix matcher currently in use. * <p> * 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. * * @param suffixMatcher the suffix matcher to use, null ignored * @return this, to enable chaining * @throws IllegalArgumentException if the suffix matcher is null */ public StrSubstitutor setVariableSuffixMatcher(StrMatcher suffixMatcher) { if (suffixMatcher == null) { throw new IllegalArgumentException("Variable suffix matcher must not be null!"); } this.suffixMatcher = suffixMatcher; return this; } /** * Sets the variable suffix to use. * <p> * 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. * * @param suffix the suffix character to use * @return this, to enable chaining */ public StrSubstitutor setVariableSuffix(char suffix) { return setVariableSuffixMatcher(StrMatcher.charMatcher(suffix)); } /** * Sets the variable suffix to use. * <p> * The variable suffix is the characer or characters that identify the * end of a variable. This method allows a string suffix to be easily set. * * @param suffix the suffix for variables, not null * @return this, to enable chaining * @throws IllegalArgumentException if the suffix is null */ public StrSubstitutor setVariableSuffix(String suffix) { if (suffix == null) { throw new IllegalArgumentException("Variable suffix must not be null!"); } return setVariableSuffixMatcher(StrMatcher.stringMatcher(suffix)); } // Resolver //----------------------------------------------------------------------- /** * Gets the VariableResolver that is used to lookup variables. * * @return the VariableResolver */ public StrLookup getVariableResolver() { return this.variableResolver; } /** * Sets the VariableResolver that is used to lookup variables. * * @param variableResolver the VariableResolver */ public void setVariableResolver(StrLookup variableResolver) { this.variableResolver = variableResolver; } }