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package org.jvnet.hk2.config;
/**
* {@link Translator} that does variable resolution in the Ant style.
*
*
* This implementation looks for variables in the string like
* "${xyz}" or "${abc.DEF.ghi}". The {@link #getVariableValue(String)} method
* is then used to obtain the actual value for the variable.
*
*
* "$$" works as the escape of "$", so for example "$${abc}" expands to "${abc}"
* where "${abc}" would have expanded to "value-of-abc".
* A lone "$" is left as-is, so "$abc" expands to "$abc".
*
* @author Kohsuke Kawaguchi
*/
public abstract class VariableResolver implements Translator {
public String translate(String str) throws TranslationException {
if(str.indexOf('$')==-1)
return str; // fast path for the common case
int idx = 0;
StringBuilder buf = new StringBuilder();
while(true) {
int s = str.indexOf('$',idx);
if(s==-1) {
buf.append(str,idx,str.length());
return buf.toString();
}
// copy until this '$'
buf.append(str,idx,s);
if(s+1==str.length()) {
buf.append('$'); // '$' was the last char
idx=s+1;
continue;
}
char second = str.charAt(s + 1);
switch(second) {
case '{': // variable
int e = str.indexOf('}',s+2);
if(e ==-1)
throw new TranslationException("Missing '}' at the end of \""+str+"\"");
String varName = str.substring(s+2, e);
String value;
try {
value = getVariableValue(varName);
} catch (TranslationException x) {
throw new TranslationException("Failed to expand variable ${"+varName+'}',x);
}
if (value == null)
throw new TranslationException(String.format("Undefined variable ${%s} in \"%s\"",
varName, str));
buf.append(value);
idx = e+1;
break;
case '$': // $ escape
buf.append('$');
idx=s+2;
break;
default:
buf.append('$');
idx=s+1;
break;
}
}
}
/**
* Returns the value of the variable.
*
* This class will not try to further expand variables in the returned value.
* If the implementation wants to do so, that is the implementation's responsibility.
*
* @return
* null if the variable is not found. The caller will report an error.
* When the variable is not found, it's also legal to throw {@link TranslationException},
* which is an useful technique if the implementation would like to report
* additional errors.
*/
protected abstract String getVariableValue(String varName) throws TranslationException;
}