json.JSONTree.g Maven / Gradle / Ivy

Go to download
Show more of this group Show more artifacts with this name
Show all versions of xpresso Show documentation
The most pythonic way to code in Java
The newest version!
grammar JSONTree;

options { 
tokenVocab=JSON; // reuse token types 
} 

@header {
package com.wantedtech.common.xpresso.json;

import com.wantedtech.common.xpresso.types.list;
import com.wantedtech.common.xpresso.types.tuple;
import com.wantedtech.common.xpresso.types.dict;
import com.wantedtech.common.xpresso.x;
import java.io.ByteArrayOutputStream;
import java.io.OutputStreamWriter;

}

@members {
    private Object extractNumber(String rawNumber, String rawExponent) {
        String numberBody = rawNumber;
        String exponent = (rawExponent == null) ? null : rawExponent.substring(1); // remove the 'e' prefix if there
        boolean isReal = numberBody.indexOf('.') >= 0 || exponent != null;
        if (!isReal) {
            return new Integer(numberBody);
        } else {
            double result = Double.parseDouble(numberBody);
            if (exponent != null) {
                result = result * Math.pow(10.0f, Double.parseDouble(exponent));
            }
            return new Double(result);
        }
    }
    
    private String extractString(String rawString) {
        // StringBuffers are an efficient way to modify strings
        StringBuffer sb = new StringBuffer(rawString);
        // Process character escapes
        int startPoint = 1; // skip initial quotation mark
        for (;;) {
            int slashIndex = sb.indexOf("\\", startPoint); // search for a single backslash
            if (slashIndex == -1) break;
            // Else, we have a backslash
            char escapeType = sb.charAt(slashIndex + 1);
            switch (escapeType) {
                case'u':
                    // Unicode escape.
                    String unicode = extractUnicode(sb, slashIndex);
                    sb.replace(slashIndex, slashIndex + 6, unicode); // backspace
                    break; // back to the loop

                    // note: Java's character escapes match JSON's, which is why it looks like we're replacing
                // "\b" with "\b". We're actually replacing 2 characters (slash-b) with one (backspace).
                case 'b':
                    sb.replace(slashIndex, slashIndex + 2, "\b"); // backspace
                    break;

                case 't':
                    sb.replace(slashIndex, slashIndex + 2, "\t"); // tab
                    break;

                case 'n':
                    sb.replace(slashIndex, slashIndex + 2, "\n"); // newline
                    break;

                case 'f':
                    sb.replace(slashIndex, slashIndex + 2, "\f"); // form feed
                    break;

                case 'r':
                    sb.replace(slashIndex, slashIndex + 2, "\r"); // return
                    break;

                case '\'':
                    sb.replace(slashIndex, slashIndex + 2, "\'"); // single quote
                    break;

                case '\"':
                    sb.replace(slashIndex, slashIndex + 2, "\""); // double quote
                    break;

                case '\\':
                    sb.replace(slashIndex, slashIndex + 2, "\\"); // backslash
                    break;
                    
                case '/':
                    sb.replace(slashIndex, slashIndex + 2, "/"); // solidus
                    break;

            }
            startPoint = slashIndex+1;

        }

        // remove surrounding quotes
        sb.deleteCharAt(0);
        sb.deleteCharAt(sb.length() - 1);

        return sb.toString();
    }

    private String extractUnicode(StringBuffer sb, int slashIndex) {
        // Gather the 4 hex digits, convert to an integer, translate the number to a unicode char, replace
        String result;
        String code = sb.substring(slashIndex + 2, slashIndex + 6);
        int charNum = Integer.parseInt(code, 16); // hex to integer
        // There's no simple way to go from an int to a unicode character.
        // We'll have to pass this through an output stream writer to do
        // the conversion.
        try {
            ByteArrayOutputStream baos = new ByteArrayOutputStream();
            OutputStreamWriter osw = new OutputStreamWriter(baos, "UTF-8");
            osw.write(charNum);
            osw.flush();
            result = baos.toString("UTF-8"); // Thanks to Silvester Pozarnik for the tip about adding "UTF-8" here
        } catch (Exception e) {
            e.printStackTrace();
            result = null;
        }
        return result;
    }

}

value returns [Object result]
	: s=string { $result = $s.result; } 
	| n=number { $result = $n.result; }
	| o=object { $result = $o.result; }
	| a=array { $result = $a.lst; }
	| TRUE { $result=Boolean.TRUE; }
	| FALSE { $result = Boolean.FALSE; }
	| NULL { $result = null; }
	;

string returns [String result]
	: st=String { $result = extractString($st.text); }
	;
	
object returns [dict