भले ही स्वीकृत उत्तर कुछ अच्छे उदाहरण देता है, लेकिन इनजेक्ट के साथ-साथ हैक के कुछ उदाहरण बचने से नहीं बचते हैं। कई लोग Regex (धीमे), या DataBinder.Eval पर भी बहुत भरोसा करते हैं जो .NET कोर और कुछ अन्य वातावरणों में उपलब्ध नहीं है।
इसे ध्यान में रखते हुए, मैंने एक साधारण स्टेट मशीन आधारित पार्सर लिखा है जो पात्रों के माध्यम से प्रवाहित होता है, एक StringBuilderआउटपुट पर लिखता है , चरित्र द्वारा चरित्र। इसे Stringविस्तार विधि (एस) के रूप में लागू किया जाता है और इनपुट के रूप में Dictionary<string, object>या objectपरावर्तन (प्रतिबिंब का उपयोग करके) दोनों को लिया जा सकता है ।
जब इनपुट में असंतुलित ब्रेसिज़ और / या अन्य त्रुटियां होती हैं तो यह असीमित स्तर को {{{escaping}}}और फेंकता है FormatException।
public static class StringExtension {
/// <summary>
/// Extension method that replaces keys in a string with the values of matching object properties.
/// </summary>
/// <param name="formatString">The format string, containing keys like {foo} and {foo:SomeFormat}.</param>
/// <param name="injectionObject">The object whose properties should be injected in the string</param>
/// <returns>A version of the formatString string with keys replaced by (formatted) key values.</returns>
public static string FormatWith(this string formatString, object injectionObject) {
return formatString.FormatWith(GetPropertiesDictionary(injectionObject));
}
/// <summary>
/// Extension method that replaces keys in a string with the values of matching dictionary entries.
/// </summary>
/// <param name="formatString">The format string, containing keys like {foo} and {foo:SomeFormat}.</param>
/// <param name="dictionary">An <see cref="IDictionary"/> with keys and values to inject into the string</param>
/// <returns>A version of the formatString string with dictionary keys replaced by (formatted) key values.</returns>
public static string FormatWith(this string formatString, IDictionary<string, object> dictionary) {
char openBraceChar = '{';
char closeBraceChar = '}';
return FormatWith(formatString, dictionary, openBraceChar, closeBraceChar);
}
/// <summary>
/// Extension method that replaces keys in a string with the values of matching dictionary entries.
/// </summary>
/// <param name="formatString">The format string, containing keys like {foo} and {foo:SomeFormat}.</param>
/// <param name="dictionary">An <see cref="IDictionary"/> with keys and values to inject into the string</param>
/// <returns>A version of the formatString string with dictionary keys replaced by (formatted) key values.</returns>
public static string FormatWith(this string formatString, IDictionary<string, object> dictionary, char openBraceChar, char closeBraceChar) {
string result = formatString;
if (dictionary == null || formatString == null)
return result;
// start the state machine!
// ballpark output string as two times the length of the input string for performance (avoids reallocating the buffer as often).
StringBuilder outputString = new StringBuilder(formatString.Length * 2);
StringBuilder currentKey = new StringBuilder();
bool insideBraces = false;
int index = 0;
while (index < formatString.Length) {
if (!insideBraces) {
// currently not inside a pair of braces in the format string
if (formatString[index] == openBraceChar) {
// check if the brace is escaped
if (index < formatString.Length - 1 && formatString[index + 1] == openBraceChar) {
// add a brace to the output string
outputString.Append(openBraceChar);
// skip over braces
index += 2;
continue;
}
else {
// not an escaped brace, set state to inside brace
insideBraces = true;
index++;
continue;
}
}
else if (formatString[index] == closeBraceChar) {
// handle case where closing brace is encountered outside braces
if (index < formatString.Length - 1 && formatString[index + 1] == closeBraceChar) {
// this is an escaped closing brace, this is okay
// add a closing brace to the output string
outputString.Append(closeBraceChar);
// skip over braces
index += 2;
continue;
}
else {
// this is an unescaped closing brace outside of braces.
// throw a format exception
throw new FormatException($"Unmatched closing brace at position {index}");
}
}
else {
// the character has no special meaning, add it to the output string
outputString.Append(formatString[index]);
// move onto next character
index++;
continue;
}
}
else {
// currently inside a pair of braces in the format string
// found an opening brace
if (formatString[index] == openBraceChar) {
// check if the brace is escaped
if (index < formatString.Length - 1 && formatString[index + 1] == openBraceChar) {
// there are escaped braces within the key
// this is illegal, throw a format exception
throw new FormatException($"Illegal escaped opening braces within a parameter - index: {index}");
}
else {
// not an escaped brace, we have an unexpected opening brace within a pair of braces
throw new FormatException($"Unexpected opening brace inside a parameter - index: {index}");
}
}
else if (formatString[index] == closeBraceChar) {
// handle case where closing brace is encountered inside braces
// don't attempt to check for escaped braces here - always assume the first brace closes the braces
// since we cannot have escaped braces within parameters.
// set the state to be outside of any braces
insideBraces = false;
// jump over brace
index++;
// at this stage, a key is stored in current key that represents the text between the two braces
// do a lookup on this key
string key = currentKey.ToString();
// clear the stringbuilder for the key
currentKey.Clear();
object outObject;
if (!dictionary.TryGetValue(key, out outObject)) {
// the key was not found as a possible replacement, throw exception
throw new FormatException($"The parameter \"{key}\" was not present in the lookup dictionary");
}
// we now have the replacement value, add the value to the output string
outputString.Append(outObject);
// jump to next state
continue;
} // if }
else {
// character has no special meaning, add it to the current key
currentKey.Append(formatString[index]);
// move onto next character
index++;
continue;
} // else
} // if inside brace
} // while
// after the loop, if all braces were balanced, we should be outside all braces
// if we're not, the input string was misformatted.
if (insideBraces) {
throw new FormatException("The format string ended before the parameter was closed.");
}
return outputString.ToString();
}
/// <summary>
/// Creates a Dictionary from an objects properties, with the Key being the property's
/// name and the Value being the properties value (of type object)
/// </summary>
/// <param name="properties">An object who's properties will be used</param>
/// <returns>A <see cref="Dictionary"/> of property values </returns>
private static Dictionary<string, object> GetPropertiesDictionary(object properties) {
Dictionary<string, object> values = null;
if (properties != null) {
values = new Dictionary<string, object>();
PropertyDescriptorCollection props = TypeDescriptor.GetProperties(properties);
foreach (PropertyDescriptor prop in props) {
values.Add(prop.Name, prop.GetValue(properties));
}
}
return values;
}
}
अंततः, सभी तर्क 10 मुख्य राज्यों में उबलते हैं - क्योंकि जब राज्य मशीन एक ब्रैकेट के बाहर होती है और इसी तरह एक ब्रैकेट के अंदर, तो अगला वर्ण या तो एक खुला ब्रेस होता है, एक बचा हुआ ब्रेस, एक बंद ब्रेस, एक बची हुई ब्रेस, या एक साधारण चरित्र। इन स्थितियों में से प्रत्येक को लूप की प्रगति के रूप में व्यक्तिगत रूप से नियंत्रित किया जाता है, वर्णों को आउटपुट StringBufferया कुंजी में जोड़ता है StringBuffer। जब कोई पैरामीटर बंद किया जाता है, तो कुंजी के मान का StringBufferउपयोग डिक्शनरी में पैरामर के मान को देखने के लिए किया जाता है, जो तब आउटपुट में धकेल दिया जाता है StringBuffer। अंत में, आउटपुट StringBufferका मूल्य वापस आ जाता है।