in log4j-core/src/main/java/org/apache/logging/log4j/core/lookup/StrSubstitutor.java [1015:1174]
private int substitute(
final LogEvent event,
final StringBuilder buf,
final int offset,
final int length,
List<String> priorVariables) {
final StrMatcher prefixMatcher = getVariablePrefixMatcher();
final StrMatcher suffixMatcher = getVariableSuffixMatcher();
final char escape = getEscapeChar();
final StrMatcher valueDelimiterMatcher = getValueDelimiterMatcher();
final boolean substitutionInVariablesEnabled = isEnableSubstitutionInVariables();
final boolean top = priorVariables == null;
boolean altered = false;
int lengthChange = 0;
char[] chars = getChars(buf);
int bufEnd = offset + length;
int pos = offset;
while (pos < bufEnd) {
final 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 = getChars(buf);
lengthChange--;
altered = true;
bufEnd--;
} else {
// find suffix
final int startPos = pos;
pos += startMatchLen;
int endMatchLen = 0;
int nestedVarCount = 0;
while (pos < bufEnd) {
if (substitutionInVariablesEnabled
&& (endMatchLen = prefixMatcher.isMatch(chars, pos, offset, bufEnd)) != 0) {
// found a nested variable start
nestedVarCount++;
pos += endMatchLen;
continue;
}
endMatchLen = suffixMatcher.isMatch(chars, pos, offset, bufEnd);
if (endMatchLen == 0) {
pos++;
} else {
// found variable end marker
if (nestedVarCount == 0) {
String varNameExpr =
new String(chars, startPos + startMatchLen, pos - startPos - startMatchLen);
if (substitutionInVariablesEnabled) {
// initialize priorVariables if they're not already set
if (priorVariables == null) {
priorVariables = new ArrayList<>();
}
final StringBuilder bufName = new StringBuilder(varNameExpr);
substitute(event, bufName, 0, bufName.length(), priorVariables);
varNameExpr = bufName.toString();
}
pos += endMatchLen;
final int endPos = pos;
String varName = varNameExpr;
String varDefaultValue = null;
if (valueDelimiterMatcher != null) {
final char[] varNameExprChars = varNameExpr.toCharArray();
int valueDelimiterMatchLen = 0;
for (int i = 0; i < varNameExprChars.length; i++) {
// if there's any nested variable when nested variable substitution disabled, then
// stop resolving name and default value.
if (!substitutionInVariablesEnabled
&& prefixMatcher.isMatch(varNameExprChars, i, i, varNameExprChars.length)
!= 0) {
break;
}
if (valueEscapeDelimiterMatcher != null) {
final int matchLen = valueEscapeDelimiterMatcher.isMatch(varNameExprChars, i);
if (matchLen != 0) {
final String varNamePrefix =
varNameExpr.substring(0, i) + Interpolator.PREFIX_SEPARATOR;
varName = varNamePrefix + varNameExpr.substring(i + matchLen - 1);
for (int j = i + matchLen; j < varNameExprChars.length; ++j) {
if ((valueDelimiterMatchLen =
valueDelimiterMatcher.isMatch(varNameExprChars, j))
!= 0) {
varName = varNamePrefix + varNameExpr.substring(i + matchLen, j);
varDefaultValue = varNameExpr.substring(j + valueDelimiterMatchLen);
break;
}
}
break;
} else if ((valueDelimiterMatchLen =
valueDelimiterMatcher.isMatch(varNameExprChars, i))
!= 0) {
varName = varNameExpr.substring(0, i);
varDefaultValue = varNameExpr.substring(i + valueDelimiterMatchLen);
break;
}
} else if ((valueDelimiterMatchLen =
valueDelimiterMatcher.isMatch(varNameExprChars, i))
!= 0) {
varName = varNameExpr.substring(0, i);
varDefaultValue = varNameExpr.substring(i + valueDelimiterMatchLen);
break;
}
}
}
// on the first call initialize priorVariables
if (priorVariables == null) {
priorVariables = new ArrayList<>();
priorVariables.add(new String(chars, offset, length + lengthChange));
}
// handle cyclic substitution
final boolean isCyclic = isCyclicSubstitution(varName, priorVariables);
// resolve the variable
final LookupResult resolvedResult =
isCyclic ? null : resolveVariable(event, varName, buf, startPos, endPos);
String varValue = resolvedResult == null ? null : resolvedResult.value();
if (varValue == null) {
varValue = varDefaultValue;
}
if (varValue != null) {
// recursive replace
final int varLen = varValue.length();
buf.replace(startPos, endPos, varValue);
altered = true;
int change = resolvedResult != null && resolvedResult.isLookupEvaluationAllowedInValue()
? substitute(event, buf, startPos, varLen, priorVariables)
: 0;
change = change + (varLen - (endPos - startPos));
pos += change;
bufEnd += change;
lengthChange += change;
chars = getChars(buf); // in case buffer was altered
}
// remove variable from the cyclic stack
if (!isCyclic) {
priorVariables.remove(priorVariables.size() - 1);
}
break;
}
nestedVarCount--;
pos += endMatchLen;
}
}
}
}
if (top) {
return altered ? 1 : 0;
}
return lengthChange;
}