https://freemarker.apache.org/: FreeMarker is a "template engine"; a generic tool to generate text output based on templates. (Apache Software Foundation) 
/*
 * 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 freemarker.core;

import freemarker.template.Template;


Exception thrown on lower (lexical) level parsing errors. Shouldn't reach normal FreeMarker users, as FreeMarker usually catches this and wraps it into a ParseException. This is a modified version of file generated by JavaCC from FTL.jj. You can modify this class to customize the error reporting mechanisms so long as the public interface remains compatible with the original. 
See Also:
/**
 * Exception thrown on lower (lexical) level parsing errors. Shouldn't reach normal FreeMarker users, as FreeMarker
 * usually catches this and wraps it into a {@link ParseException}.
 * 
 * This is a modified version of file generated by JavaCC from FTL.jj.
 * You can modify this class to customize the error reporting mechanisms so long as the public interface
 * remains compatible with the original.
 * 
 * @see ParseException
 */
public class TokenMgrError extends Error {
   /*
    * Ordinals for various reasons why an Error of this type can be thrown.
    */

   
Lexical error occurred.

/**
    * Lexical error occurred.
    */
   static final int LEXICAL_ERROR = 0;

   
An attempt was made to create a second instance of a static token manager.

/**
    * An attempt was made to create a second instance of a static token manager.
    */
   static final int STATIC_LEXER_ERROR = 1;

   
Tried to change to an invalid lexical state.

/**
    * Tried to change to an invalid lexical state.
    */
   static final int INVALID_LEXICAL_STATE = 2;

   
Detected (and bailed out of) an infinite loop in the token manager.

/**
    * Detected (and bailed out of) an infinite loop in the token manager.
    */
   static final int LOOP_DETECTED = 3;

   
Indicates the reason why the exception is thrown. It will have
one of the above 4 values.

/**
    * Indicates the reason why the exception is thrown. It will have
    * one of the above 4 values.
    */
   int errorCode;

   private String detail;
   private Integer lineNumber, columnNumber;
   private Integer endLineNumber, endColumnNumber;

   
Replaces unprintable characters by their espaced (or unicode escaped)
equivalents in the given string

/**
    * Replaces unprintable characters by their espaced (or unicode escaped)
    * equivalents in the given string
    */
   protected static final String addEscapes(String str) {
      StringBuilder retval = new StringBuilder();
      char ch;
      for (int i = 0; i < str.length(); i++) {
        switch (str.charAt(i))
        {
           case 0 :
              continue;
           case '\b':
              retval.append("\\b");
              continue;
           case '\t':
              retval.append("\\t");
              continue;
           case '\n':
              retval.append("\\n");
              continue;
           case '\f':
              retval.append("\\f");
              continue;
           case '\r':
              retval.append("\\r");
              continue;
           case '\"':
              retval.append("\\\"");
              continue;
           case '\'':
              retval.append("\\\'");
              continue;
           case '\\':
              retval.append("\\\\");
              continue;
           default:
              if ((ch = str.charAt(i)) < 0x20 || ch > 0x7e) {
                 String s = "0000" + Integer.toString(ch, 16);
                 retval.append("\\u" + s.substring(s.length() - 4, s.length()));
              } else {
                 retval.append(ch);
              }
              continue;
        }
      }
      return retval.toString();
   }

   
Returns a detailed message for the Error when it's thrown by the
token manager to indicate a lexical error.
Parameters : 
   EOFSeen     : indicates if EOF caused the lexicl error
   curLexState : lexical state in which this error occurred
   errorLine   : line number when the error occurred
   errorColumn : column number when the error occurred
   errorAfter  : prefix that was seen before this error occurred
   curchar     : the offending character
Note: You can customize the lexical error message by modifying this method.

/**
    * Returns a detailed message for the Error when it's thrown by the
    * token manager to indicate a lexical error.
    * Parameters : 
    *    EOFSeen     : indicates if EOF caused the lexicl error
    *    curLexState : lexical state in which this error occurred
    *    errorLine   : line number when the error occurred
    *    errorColumn : column number when the error occurred
    *    errorAfter  : prefix that was seen before this error occurred
    *    curchar     : the offending character
    * Note: You can customize the lexical error message by modifying this method.
    */
   protected static String LexicalError(boolean EOFSeen, int lexState, int errorLine, int errorColumn, String errorAfter, char curChar) {
      return("Lexical error: encountered " +
           (EOFSeen ? "<EOF> " : ("\"" + addEscapes(String.valueOf(curChar)) + "\"") + " (" + (int) curChar + "), ") +
           "after \"" + addEscapes(errorAfter) + "\".");
   }

   
You can also modify the body of this method to customize your error messages.
For example, cases like LOOP_DETECTED and INVALID_LEXICAL_STATE are not
of end-users concern, so you can return something like : 
    "Internal Error : Please file a bug report .... "
from this method for such cases in the release version of your parser.

/**
    * You can also modify the body of this method to customize your error messages.
    * For example, cases like LOOP_DETECTED and INVALID_LEXICAL_STATE are not
    * of end-users concern, so you can return something like : 
    *
    *     "Internal Error : Please file a bug report .... "
    *
    * from this method for such cases in the release version of your parser.
    */
   @Override
public String getMessage() {
      return super.getMessage();
   }

   /*
    * Constructors of various flavors follow.
    */

   public TokenMgrError() {
   }

   public TokenMgrError(String detail, int reason) {
      super(detail);  // the "detail" must not contain location information, the "message" might does
      this.detail = detail;
      errorCode = reason;
   }

   
Since:2.3.20
Deprecated:If you know the end position, use TokenMgrError(String, int, int, int, int, int) instead.
/**
    * @since 2.3.20
    * 
    * @deprecated If you know the end position, use {@link #TokenMgrError(String, int, int, int, int, int)} instead.
    */
   @Deprecated
public TokenMgrError(String detail, int reason, int errorLine, int errorColumn) {
       this(detail, reason, errorLine, errorColumn, 0, 0);
       this.endLineNumber = null; 
       this.endColumnNumber = null; 
    }
   
   
Since:2.3.21
/**
    * @since 2.3.21
    */
   public TokenMgrError(String detail, int reason,
           int errorLine, int errorColumn,
           int endLineNumber, int endColumnNumber) {
       super(detail);  // the "detail" must not contain location information, the "message" might does
       this.detail = detail;
       errorCode = reason;
       
       this.lineNumber = Integer.valueOf(errorLine);  // In J2SE there was no Integer.valueOf(int)
       this.columnNumber = Integer.valueOf(errorColumn);
       this.endLineNumber = Integer.valueOf(endLineNumber); 
       this.endColumnNumber = Integer.valueOf(endColumnNumber); 
    }

   
Overload for JavaCC 6 compatibility.

Since:2.3.24
/**
    * Overload for JavaCC 6 compatibility.
    * 
    * @since 2.3.24
    */
   TokenMgrError(boolean EOFSeen, int lexState, int errorLine, int errorColumn, String errorAfter, int curChar, int reason) {
       this(EOFSeen, lexState, errorLine, errorColumn, errorAfter, (char) curChar, reason);
   }
   
   public TokenMgrError(boolean EOFSeen, int lexState, int errorLine, int errorColumn, String errorAfter, char curChar, int reason) {
      this(LexicalError(EOFSeen, lexState, errorLine, errorColumn, errorAfter, curChar), reason);
      
      this.lineNumber = Integer.valueOf(errorLine);  // In J2SE there was no Integer.valueOf(int)
      this.columnNumber = Integer.valueOf(errorColumn);
      // We blame the single character that can't be the start of a legal token: 
      this.endLineNumber = this.lineNumber; 
      this.endColumnNumber = this.columnNumber; 
   }

   
1-based line number of the unexpected character(s).

Since:2.3.20
/**
    * 1-based line number of the unexpected character(s).
    * 
    * @since 2.3.20
    */
   public Integer getLineNumber() {
      return lineNumber;
   }
    
   
1-based column number of the unexpected character(s).

Since:2.3.20
/**
    * 1-based column number of the unexpected character(s).
    * 
    * @since 2.3.20
    */
   public Integer getColumnNumber() {
      return columnNumber;
   }
   
   
Returns the 1-based line at which the last character of the wrong section is. This will be usually (but not always) the same as getLineNumber() because the lexer can only point to the single character that doesn't match any patterns. 
Since:2.3.21
/**
    * Returns the 1-based line at which the last character of the wrong section is. This will be usually (but not
    * always) the same as {@link #getLineNumber()} because the lexer can only point to the single character that
    * doesn't match any patterns.
    * 
    * @since 2.3.21
    */
   public Integer getEndLineNumber() {
      return endLineNumber;
   }

   
Returns the 1-based column at which the last character of the wrong section is. This will be usually (but not always) the same as getColumnNumber() because the lexer can only point to the single character that doesn't match any patterns. 
Since:2.3.21
/**
    * Returns the 1-based column at which the last character of the wrong section is. This will be usually (but not
    * always) the same as {@link #getColumnNumber()} because the lexer can only point to the single character that
    * doesn't match any patterns.
    * 
    * @since 2.3.21
    */
   public Integer getEndColumnNumber() {
      return endColumnNumber;
   }

   public String getDetail() {
       return detail;
   }

   public ParseException toParseException(Template template) {
       return new ParseException(getDetail(),
               template,
               getLineNumber() != null ? getLineNumber().intValue() : 0,
               getColumnNumber() != null ? getColumnNumber().intValue() : 0,
               getEndLineNumber() != null ? getEndLineNumber().intValue() : 0,
               getEndColumnNumber() != null ? getEndColumnNumber().intValue() : 0);
   }
   
}