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package org.apache.jasper.compiler;
/**
* This class implements a parser for EL expressions.
*
* It takes strings of the form xxx${..}yyy${..}zzz etc, and turn it into
* a ELNode.Nodes.
*
* Currently, it only handles text outside ${..} and functions in ${ ..}.
*
* @author Kin-man Chung
*/
public class ELParser {
private Token curToken; // current token
private ELNode.Nodes expr;
private ELNode.Nodes ELexpr;
private int index; // Current index of the expression
private String expression; // The EL expression
private boolean escapeBS; // is '\' an escape char in text outside EL?
private boolean isDollarExpr;
private static final String reservedWords[] = {
"and", "div", "empty", "eq", "false",
"ge", "gt", "instanceof", "le", "lt", "mod",
"ne", "not", "null", "or", "true"};
public ELParser(String expression) {
index = 0;
this.expression = expression;
expr = new ELNode.Nodes();
}
/**
* Parse an EL expression
* @param expression The input expression string of the form
* ( (Char* | (('${' | '#{') Char* '}') )+
* @return Parsed EL expression in ELNode.Nodes
*/
public static ELNode.Nodes parse(String expression) {
ELParser parser = new ELParser(expression);
while (parser.hasNextChar()) {
String text = parser.skipUntilEL();
if (text.length() > 0) {
parser.expr.add(new ELNode.Text(text));
}
ELNode.Nodes elexpr = parser.parseEL();
if (! elexpr.isEmpty()) {
parser.expr.add(new ELNode.Root(elexpr, parser.isDollarExpr));
}
}
return parser.expr;
}
/**
* Parse an EL expression string '${...} or #{...}'
*@return An ELNode.Nodes representing the EL expression
* TODO: Currently only parsed into functions and text strings. This
* should be rewritten for a full parser.
*/
private ELNode.Nodes parseEL() {
StringBuffer buf = new StringBuffer();
ELexpr = new ELNode.Nodes();
while (hasNext()) {
curToken = nextToken();
if (curToken instanceof Char) {
if (curToken.toChar() == '}') {
break;
}
buf.append(curToken.toChar());
} else {
// Output whatever is in buffer
if (buf.length() > 0) {
ELexpr.add(new ELNode.ELText(buf.toString()));
}
if (!parseFunction()) {
ELexpr.add(new ELNode.ELText(curToken.toString()));
}
}
}
if (buf.length() > 0) {
ELexpr.add(new ELNode.ELText(buf.toString()));
}
return ELexpr;
}
/**
* Parse for a function
* FunctionInvokation ::= (identifier ':')? identifier '('
* (Expression (,Expression)*)? ')'
* Note: currently we don't parse arguments
*/
private boolean parseFunction() {
if (! (curToken instanceof Id) || isELReserved(curToken.toString())) {
return false;
}
String s1 = null; // Function prefix
String s2 = curToken.toString(); // Function name
int mark = getIndex();
if (hasNext()) {
Token t = nextToken();
if (t.toChar() == ':') {
if (hasNext()) {
Token t2 = nextToken();
if (t2 instanceof Id) {
s1 = s2;
s2 = t2.toString();
if (hasNext()) {
t = nextToken();
}
}
}
}
if (t.toChar() == '(') {
ELexpr.add(new ELNode.Function(s1, s2));
return true;
}
}
setIndex(mark);
return false;
}
/**
* Test if an id is a reserved word in EL
*/
private boolean isELReserved(String id) {
int i = 0;
int j = reservedWords.length;
while (i < j) {
int k = (i+j)/2;
int result = reservedWords[k].compareTo(id);
if (result == 0) {
return true;
}
if (result < 0) {
i = k+1;
} else {
j = k;
}
}
return false;
}
/**
* Skip until an EL expression ('${' or '#{') is reached, allowing escape
* sequences '\\', '\$', and '\#'.
* @return The text string up to the EL expression
*/
private String skipUntilEL() {
char prev = 0;
StringBuffer buf = new StringBuffer();
while (hasNextChar()) {
char ch = nextChar();
if (prev == '\\') {
prev = 0;
if (ch == '\\') {
buf.append('\\');
if (!escapeBS)
prev = '\\';
} else if (ch == '$' || ch == '#') {
buf.append(ch);
}
// else error!
} else if (prev == '$' || prev == '#') {
if (ch == '{') {
this.isDollarExpr = (prev == '$');
prev = 0;
break;
}
buf.append(prev);
if (ch == '\\' || ch == '$' || ch == '#') {
prev = ch;
} else {
buf.append(ch);
}
} else if (ch == '\\' || ch == '$' || ch == '#') {
prev = ch;
} else {
buf.append(ch);
}
}
if (prev != 0) {
buf.append(prev);
}
return buf.toString();
}
/*
* @return true if there is something left in EL expression buffer other
* than white spaces.
*/
private boolean hasNext() {
skipSpaces();
return hasNextChar();
}
/*
* @return The next token in the EL expression buffer.
*/
private Token nextToken() {
skipSpaces();
if (hasNextChar()) {
char ch = nextChar();
if (Character.isJavaIdentifierStart(ch)) {
StringBuffer buf = new StringBuffer();
buf.append(ch);
while ((ch = peekChar()) != -1 &&
Character.isJavaIdentifierPart(ch)) {
buf.append(ch);
nextChar();
}
return new Id(buf.toString());
}
if (ch == '\'' || ch == '"') {
return parseQuotedChars(ch);
} else {
// For now...
return new Char(ch);
}
}
return null;
}
/*
* Parse a string in single or double quotes, allowing for escape sequences
* '\\', and ('\"', or "\'")
*/
private Token parseQuotedChars(char quote) {
StringBuffer buf = new StringBuffer();
buf.append(quote);
while (hasNextChar()) {
char ch = nextChar();
if (ch == '\\') {
ch = nextChar();
if (ch == '\\' || ch == quote) {
buf.append(ch);
}
// else error!
} else if (ch == quote) {
buf.append(ch);
break;
} else {
buf.append(ch);
}
}
return new QuotedString(buf.toString());
}
/*
* A collection of low level parse methods dealing with character in
* the EL expression buffer.
*/
private void skipSpaces() {
while (hasNextChar()) {
if (expression.charAt(index) > ' ')
break;
index++;
}
}
private boolean hasNextChar() {
return index < expression.length();
}
private char nextChar() {
if (index >= expression.length()) {
return (char)-1;
}
return expression.charAt(index++);
}
private char peekChar() {
if (index >= expression.length()) {
return (char)-1;
}
return expression.charAt(index);
}
private int getIndex() {
return index;
}
private void setIndex(int i) {
index = i;
}
/*
* Represents a token in EL expression string
*/
private static class Token {
char toChar() {
return 0;
}
public String toString() {
return "";
}
}
/*
* Represents an ID token in EL
*/
private static class Id extends Token {
String id;
Id(String id) {
this.id = id;
}
public String toString() {
return id;
}
}
/*
* Represents a character token in EL
*/
private static class Char extends Token {
private char ch;
Char(char ch) {
this.ch = ch;
}
char toChar() {
return ch;
}
public String toString() {
return (Character.valueOf(ch)).toString();
}
}
/*
* Represents a quoted (single or double) string token in EL
*/
private static class QuotedString extends Token {
private String value;
QuotedString(String v) {
this.value = v;
}
public String toString() {
return value;
}
}
}
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