使用 Java 将 JSON 文件转换为 RDF 格式

Question

Here I want to convert the JSON file into RDF. Here is the JSON

{
"glossary": {
    "title": "example glossary",
    "GlossDiv": {
        "title": "S",
        "GlossList": {
            "GlossEntry": {
                "ID": "SGML",
                "SortAs": "SGML",
                "GlossTerm": "Standard Generalized Markup Language",
                "Acronym": "SGML",
                "Abbrev": "ISO 8879:1986",
                "GlossDef": {
                    "para": "A meta-markup language, used to create markup languages such as DocBook.",
                    "GlossSeeAlso": ["GML", "XML"]
                },
                "GlossSee": "markup"
            }
        }
    }
}
}

I could not find a proper way to convert it into RDF.

Answer 1

There is no standard way to interpret JSON as RDF. There are several ways you can generate RDF from a JSON file though (in Java or otherwise). You could simply use a JSON parser implemented in Java, then extract the relevant parts and build an RDF graph using a Java library for RDF such as Apache Jena or RDF4J (formerly known as Sesame ). However, there are other ways that could make the task much easier:

• Transform the JSON file into a JSON-LD file by adding a @context to it. This works well for simple cases but is not sufficient to cover many relevant cases.
• Use RML , a language for expressing mappings from various data formats (including JSON) to RDF. It has a reference implementation in Java. RML is an extension of R2RML, so it can also map relational data to RDF, and if you are familiar with R2RML , it is relatively easy to understand how RML works. There is also a graphical editor , but it seems it is not available for download.
• Use SPARQL-Generate , a language for expressing mappings from non-RDF data sources (including JSON) to RDF. It has a reference implementation based on Jena. It extends SPARQL, so if you are familiar with SPARQL, it should be quite easy to use it. It can be tested online .

Disclaimer: I contributed to SPARQL-Generate.

Answer 2

If your aim is to simply get valid RDF without making any decisions about structure, you could trivially add a @context object and turn the existing JSON into JSON-LD, eg

{
  "@context": {"@vocab": "http://example.org/ontology#"},
  "glossary": {
    "title": "example glossary",
    "GlossDiv": {
        "title": "S",
        "GlossList": {
            "GlossEntry": {
                "ID": "SGML",
                "SortAs": "SGML",
                "GlossTerm": "Standard Generalized Markup Language",
                "Acronym": "SGML",
                "Abbrev": "ISO 8879:1986",
                "GlossDef": {
                    "para": "A meta-markup language, used to create markup languages such as DocBook.",
                    "GlossSeeAlso": ["GML", "XML"]
                },
                "GlossSee": "markup"
            }
        }
    }
  }
}

This can then be interpreted as RDF using an appropriate RDF/JSON-LD library, the RDF structure would be:

@prefix ns0: <http://example.org/ontology#> .

[] ns0:glossary [
    ns0:GlossDiv [
      ns0:GlossList [ ns0:GlossEntry [
          ns0:Abbrev "ISO 8879:1986" ;
          ns0:Acronym "SGML" ;
          ns0:GlossDef [
            ns0:GlossSeeAlso "GML", "XML" ;
            ns0:para "A meta-markup language, used to create markup languages such as DocBook."
          ] ;
          ns0:GlossSee "markup" ;
          ns0:GlossTerm "Standard Generalized Markup Language" ;
          ns0:ID "SGML" ;
          ns0:SortAs "SGML"
        ] ] ;
      ns0:title "S"
    ] ;
    ns0:title "example glossary"
  ] .

This is perhaps strange RDF, but it can be loaded and manipulated using RDF tools.

You can play with the example in the json-ld playground

Answer 3

You can convert the JSON file into RDF using RML . To achieve that, you need to create some mapping rules first. These mapping rules are used by an RML processor to transform your input data into RDF. An example of an RML processor is the RML mapper .

1. Create an RML LogicalSource . This describes how and where the RML processor should access the input data:

<#LogicalSource>
    a rml:logicalSource;
    rml:source "data.json";
    rml:referenceFormulation ql:JSONPath;
    rml:iterator "$.glossary".

This RDF snippet tells an RML processor that he has to retrieve data.json and iterate over the data with a JSONPath expression ( ql:JSONPath ) which is specified by rml:iterator .

2. Create a TriplesMap . This provides an RML processor information about how the input data should be transformed into RDF. An example is given for the provided data:

<#GlossaryMapping>
    a rr:TriplesMap;
    rml:logicalSource <#LogicalSource>;

    rr:subjectMap [
        rr:template "http://example.org/glossary/{title}";
    ];

    rr:predicateObjectMap [
        rr:predicate ex:title;
        rr:objectMap [
            rml:reference "title";
        ];
    ].

The TriplesMap uses the created LogicalSource to access the data. The TriplesMap will make sure that an RML processor creates triples with http://example.org/glossary/{title} as subject, ex:title as predicate and the value of the JSON property title as object

3. TriplesMaps can also be linked with each other. If you have an entry of a list ( GlossEntry ) to a higher element glossary for example, you can write the following mapping rules:

<#GlossaryMapping>
    a rr:TriplesMap;
    rml:logicalSource <#LogicalSource>;

    rr:subjectMap [
        rr:template "http://example.org/glossary/{title}";
    ];

rr:predicateObjectMap [
        rr:predicate ex:glossDiv;
        rr:objectMap [
            rr:parentTriplesMap <#GlossListEntryMapping>;
            rr:child "GlossDiv.title";
            rr:parent "GlossDiv.title";
        ];
    ].

<#GlossListEntryMapping>
    a rr:TriplesMap;
    rml:logicalSource <#LogicalSource>;

    rr:subjectMap [
        rr:template "http://example.org/entry/{GlossDiv.title}";
    ];

Both TriplesMaps will be joined with each other taking into account the provided rr:joinCondition . If no join condition is provided, every subject of the child will be joined with every subject of the parent.

Mapping rules

I left out some JSON properties in this full example to keep it concise.

@base <http://example.org> .
@prefix rr: <http://www.w3.org/ns/r2rml#> .
@prefix rml: <http://semweb.mmlab.be/ns/rml#> .
@prefix ql: <http://semweb.mmlab.be/ns/ql#> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
@prefix ex: <http://example.org/ns#> .

<#LogicalSource>
    a rml:logicalSource;
    rml:source "data.json";
    rml:referenceFormulation ql:JSONPath;
    rml:iterator "$.glossary".

<#GlossaryMapping>
    a rr:TriplesMap;
    rml:logicalSource <#LogicalSource>;

    rr:subjectMap [
        rr:template "http://example.org/glossary/{title}";
    ];

    rr:predicateObjectMap [
        rr:predicate ex:title;
        rr:objectMap [
            rml:reference "title";
        ];
    ];

    rr:predicateObjectMap [
        rr:predicate ex:glossDiv;
        rr:objectMap [
            rr:parentTriplesMap <#GlossListEntryMapping>;
            rr:child "GlossDiv.title";
            rr:parent "GlossDiv.title";
        ];
    ].

<#GlossListEntryMapping>
    a rr:TriplesMap;
    rml:logicalSource <#LogicalSource>;

    rr:subjectMap [
        rr:template "http://example.org/entry/{GlossDiv.title}";
    ];

    rr:predicateObjectMap [
        rr:predicate ex:ID;
        rr:objectMap [
            rml:reference "GlossDiv.GlossList.GlossEntry.ID" 
        ];
    ];

    rr:predicateObjectMap [
        rr:predicate ex:Abbrev;
        rr:objectMap [
            rml:reference "GlossDiv.GlossList.GlossEntry.Abbrev" 
        ];
    ];

    # Other properties can be mapped too if needed

    rr:predicateObjectMap [
        rr:predicate ex:glossSeeAlso;
        rr:objectMap [ # Mapping arrays can also be done
            rml:reference "GlossDiv.GlossList.GlossEntry.GlossDef.GlossSeeAlso.[*]";
        ];
    ].

Output

<http://example.org/entry/S> <http://example.org/ns#glossSeeAlso> "GML".
<http://example.org/entry/S> <http://example.org/ns#glossSeeAlso> "XML".
<http://example.org/entry/S> <http://example.org/ns#ID> "SGML".
<http://example.org/entry/S> <http://example.org/ns#Abbrev> "ISO 8879:1986".
<http://example.org/glossary/example%20glossary> <http://example.org/ns#title> "example glossary".
<http://example.org/glossary/example%20glossary> <http://example.org/ns#glossDiv> <http://example.org/entry/S>.

Note : I contribute to RML and its technologies.

Answer 4

If I understand your question correctly, I recommend using Apache Jena , Apache's open source semantic web library.

Here is an RDF creation tutorial .

I've also found JSON2RDF , a project that claims to utilize Jena in creating a declerative language for converting JSONs into RDFs, but I have not tested it myself and the docs are vague. Please share your experience if you do end up looking into it.

Answer 5

We have released open-source JSON2RDF converter (not to be confused with the JSON2RDF mentioned by vaiden) that allows you to do exactly that: https://github.com/AtomGraph/JSON2RDF

JSON2RDF + SPARQL can be used as a more flexible alternative to JSON-LD + @context .

Answer 6

We're providing a JSON to JSONLD converting service: https://json2ld.mapper.tokyo/

First, you paste or upload your JSON data, then it instantly generates their JSONLD version.

It automatically maps some existing vocabularies such as schema.org if there's a matching term in the JSON data such as "name", which is mapped to https://schema.org/name .

You can edit which vocabularies or terms are mapped and publish your context from your GitHub repo.

Answer 7

I spent some time recently to paste some older java code together to create a command line tool named 'oi'.

https://github.com/jschnasse/oi

Call

oi stack44753298.json -t turtle

Prints

_:b0 <info:oi/glossary> _:b1 .

_:b1 <info:oi/GlossDiv> _:b2 .

_:b2 <info:oi/GlossList> _:b3 .

_:b3 <info:oi/GlossEntry> _:b4 .

_:b4 <info:oi/Abbrev> "ISO 8879:1986";
  <info:oi/Acronym> "SGML";
  <info:oi/GlossDef> _:b5 .

_:b5 <info:oi/GlossSeeAlso> "GML", "XML";
  <info:oi/para> "A meta-markup language, used to create markup languages such as DocBook." .

_:b4 <info:oi/GlossSee> "markup";
  <info:oi/GlossTerm> "Standard Generalized Markup Language";
  <info:oi/ID> "SGML";
  <info:oi/SortAs> "SGML" .

_:b2 <info:oi/title> "S" .

_:b1 <info:oi/title> "example glossary" .

The tool uses a very rough approach to transform rdf to json and vice versa. For the json to rdf case it creates an adhoc context just by putting all json keys into an info:namespace . After that it uses the context to read in the json as jsonld. Exactly like already described in this thread by brinxmat .

It follows roughly the ideas I wrote up in recent stackoverflow threads:

• How do I add a start and end time to a RDF triple?
• How to convert RDF to pretty nested JSON using java rdf4j

Answer 8

Read JSON with this JSON parser to Java objects and create rdf with Java objects which is previously read.

package your_package;

import java.io.ByteArrayInputStream;  

import java.io.ByteArrayOutputStream; 
import java.io.IOException; 
import java.io.InputStream; 
import java.io.OutputStream;  
import java.io.PrintStream;
import java.nio.charset.Charset; 
import java.util.AbstractList;  
import java.util.ArrayList;  
import java.util.Collection;
import java.util.HashMap; 
import java.util.Iterator;  
import java.util.List; 
import java.util.Map;

<html>


 /**
     * JSON is an open standard format that uses human-readable text to transmit
     * Data objects consisting of attribute–value pairs. It is used primarily to
     * Transmit data between a server and web application, as an alternative to XML.
     *  
     * JSON's basic types are:
     * <ul>
     * <li><b>Number</b>: a signed decimal number that may contain a fractional part
     * And may use exponential E notation. JSON does not allow non-numbers like NaN,
     * Nor does it make any distinction between integer and floating-point. (Even
     * Though JavaScript uses a double-precision floating-point format for all its
     * Numeric values, other languages implementing JSON may encode numbers
     * differently) </li>
     * <li><b>String</b>: a sequence of zero or more Unicode characters. Strings are
     * Delimited with double-quotation marks and support a backslash escaping
     * syntax.</li>
     * <li><b>Boolean</b>: either of the values {@code true} or {@code false}</li>
     * <li><b>Array</b>: an ordered list of zero or more values, each of which may
     * Be of any type. Arrays use square bracket notation with elements being
     * comma-separated.</li>
     * <li><b>Object</b>: an unordered collection of name/value pairs where the
     * Names (also called keys) are strings. Since objects are intended to represent
     * Associative arrays, it is recommended, though not required, that each key is
     * Unique within an object. Objects are delimited with curly brackets and use
     * Commas to separate each pair, while within each pair the colon {@code ':'}
     * Character separates the key or name from its value.</li>
     * <li><b>null</b>: An empty value, using the word null</li>
     * </ul>
     * Conversion table:
     * <table border='1'>
     * <tr><td>java.util.Map</td><td>JSON Object {"key":[0,2,3]}</td></tr>
     * <tr><td>java.util.Collection</td><td>JSON Array [0,1,2,"string"]</td></tr>
     * <tr><td>java.lang.String</td><td>JSON String "example"</td></tr>
     * <tr><td>java.lang.Boolean</td><td>JSON Boolean (true/false) </td></tr>
     * <tr><td>java.lang.Number</td><td>JSON Number (-2.5E2) </td></tr>
     * <tr><td>null</td><td>JSON Null (null) </td></tr>
     * </table>
     * Any other object will be write with the next formula:  
     * <u>{@code obj.toString()}</u>. For example:
     * {@Code write (out, new java.lang.object())}. The output stream will be
     * Contains the hashcode of newly created object because the default object
     * toString() method returns the object hashcode. This class supported the
     * Duplicated keys in the object map.
     *  
     * The JavaScript Object Notation (JSON) Data Interchange Format:
     * <A href='http://tools.ietf.org/html/rfc7159'>RFC-7159</a>
     *
     * @See DuplicatedKeyList
     */
public class Json {
    /**
     * This field represents when the json object is finished, no more available
     * data to processing.
     */
    private static final Object close = new Object();
    /**
     * The step offsets in the rows.
     */
    private static final int writeSpaceCount = 1;
    /**
     * 'n' 'u' 'l' 'l'
     */
    public static final byte[] NULL = new byte[]{'n', 'u', 'l', 'l'};
    /**
     * The null identifer, also called: the first character of null.
     */
    public static final int NULL_LOWER = 'n';
    /**
     * The null identifer, also called: the first character of null (uppercase).
     */
    public static final int NULL_UPPER = 'N';
    /**
     * The first character of {@code true}.
     */
    public static final int TRUE = 't';
    /**
     * The first character of {@code true} (uppercase).
     */
    public static final int TRUE_UPPER = 'T';
    /**
     * The first character of {@code false}.
     */
    public static final int FALSE = 'f';
    /**
     * The first character of {@code false} (uppercase).
     */
    public static final int FALSE_UPPER = 'F';
    /**
     * Colon ascii value
     */
    public static final int COLON = ':';
    /**
     * Comma ascii value
     */
    public static final int COMMA = ',';
    /**
     * left bracket (the list identifier, first character)
     */
    public static final int LEFT_BRACKET = '[';
    /**
     * left brace (the map identifier, first character)
     */
    public static final int LEFT_BRACE = '{';
    /**
     * right bracket (the list identifier, last character)
     */
    public static final int RIGHT_BRACKET = ']';
    /**
     * right bracket (the map identifier, last character)
     */
    public static final int RIGHT_BRACE = '}';
    /**
     * the string identifier: {@code "}
     */
    public static final int STRING = '"';
    /**
     * the space ascii value
     */
    public static final int SP = ' ';
    /**
     * the backslash ascii value
     */
    public static final int BS = '\\';
    /**
     * the CR (carriage return) ascii value
     */
    public static final int CR = 13;
    /**
     * the line feed ascii value
     */
    public static final int LF = 10;
    /**
     * the end of file identifier
     */
    public static final int EOF = -1;
    /**
     * end of line identifier (CR + LF)
     */
    public static final byte[] EOL = new byte[]{CR, LF};

    /**
     * the byte array buffer to read
     */
    private final ByteArrayOutputStream buf = new ByteArrayOutputStream();

    /**
     * Creates a new JSON which can read and write json objects.
     */
    public Json() {
    }

    /**
     * Creates a new empty map.
     *
     * @return a new empty map.
     */
    private Map createEmptyMap() {
        return new HashMap();
    }

    /**
     * Writes a specified object {@code obj} to a specified output stream
     * {@code out}, also called: creates a json document from the specified
     * object. Duplicated keys are supported. Conversion table: see JSON class
     * javadoc.
     *
     * @param out the specified output stream
     * @param obj the specified object
     * @throws IOException If IO Error Occurs.
     * @see Json
     */
    public void write(PrintStream out, Object obj) throws IOException {
        write(out, obj, false);
    }

    /**
     * Writes a specified object {@code obj} to a specified print stream
     * {@code out}, also called: creates a json document from the specified
     * object. Duplicated keys are supported. Conversion table: see JSON class
     * javadoc.
     *
     * @param out the specified print stream
     * @param obj the specified object
     * @param format {@code true} if the output is formatted, otherwise
     * {@code false}.
     * @throws IOException If IO Error Occurs.
     * @see Json
     * @see DuplicatedKeyList
     */
    public void write(PrintStream out, Object obj, boolean format) throws IOException {
        write(out, obj, format, 0);
    }

    /**
     * Writes a specified object {@code obj} to a specified print stream
     * {@code out}, also called: creates a json document from the specified
     * object. Duplicated keys are supported. Conversion table: see JSON class
     * javadoc.
     *
     * @param out the specified print stream
     * @param obj the specified object
     * @param format {@code true} if the output is formatted, otherwise
     * {@code false}.
     * @param charset the charset which represents the json document encodings
     * @param depth the current depth from the root element
     * @throws IOException If IO Error Occurs.
     * @see Json
     * @see DuplicatedKeyList
     */
    private synchronized void write(PrintStream out, Object obj, boolean format, int depth) throws IOException {
        if (obj == null) {
            out.write(NULL);
            out.flush();
            return;
        }
        if (obj instanceof String) {
            out.write(STRING);
            out.print(escape((String) obj));
            out.write(STRING);
            out.flush();
            return;
        } else if (obj instanceof Map) {
            out.write(LEFT_BRACE);
            Map map = (Map) obj;
            Iterator<Map.Entry> it = map.entrySet().iterator();
            Map.Entry entry;
            while (it.hasNext()) {
                entry = it.next();
                String key = escape(entry.getKey().toString());
                Object val = entry.getValue();
                if (val instanceof DuplicatedKeyList) {
                    writeMulti(out, key, (List) val, format, depth);
                } else {
                    if (format) {
                        writeBreak(out, depth + writeSpaceCount);
                    }
                    write(out, key, format, depth + writeSpaceCount);
                    out.write(COLON);
                    if (format) {
                        writeSpace(out, writeSpaceCount);
                    }
                    write(out, val, format, depth + writeSpaceCount);
                }
                if (it.hasNext()) {
                    out.write(COMMA);
                }
            }
            if (format) {
                writeBreak(out, depth);
            }
            out.write(RIGHT_BRACE);
            out.flush();
            return;
        } else if (obj instanceof Collection) {
            out.write(LEFT_BRACKET);
            Iterator it = ((Collection) obj).iterator();
            while (it.hasNext()) {
                if (format) {
                    writeBreak(out, depth + writeSpaceCount);
                }
                write(out, it.next(), format, depth + writeSpaceCount);
                if (it.hasNext()) {
                    out.write(COMMA);
                }
            }
            if (format) {
                writeBreak(out, depth);
            }
            out.write(RIGHT_BRACKET);
            out.flush();
            return;
        }
        if (obj instanceof Number || obj instanceof Boolean) {
            out.print(obj);
        } else {
            out.write(STRING);
            out.print(escape(obj.toString()));
            out.write(STRING);
        }
        out.flush();
    }

    /**
     * Reads a specified input stream {@code in} which contains json elements
     * and returns the java object representation of json elements. Conversion
     * table: see JSON class javadoc.
     *
     * @param in the specified input stream
     * @return the java object representation of json elements.
     * @throws IOException If IO Error Occurs.
     * @see Json
     * @see DuplicatedKeyList
     */
    public Object read(InputStream in) throws IOException {
        return read(in, Charset.forName("UTF-8"));
    }

    /**
     * Reads a specified input stream {@code in} which contains json elements
     * and returns the java object representation of json elements. Conversion
     * table: see JSON class javadoc.
     *
     * @param in the specified input stream
     * @param charset the json document encodings
     * @return the java object representation of json elements.
     * @throws IOException If IO Error Occurs.
     * @see Json
     * @see DuplicatedKeyList
     */
    public synchronized Object read(InputStream in, Charset charset) throws IOException {
        int b;
        while ((b = in.read()) != EOF) {
            if (b > 32 && b != COMMA) {
                switch (b) {
                    //list
                    case LEFT_BRACKET: {
                        List list = new ArrayList();
                        Object obj;
                        while ((obj = read(in, charset)) != close) {
                            if (obj instanceof Finish) {
                                list.add(((Finish) obj).val);
                                break;
                            } else {
                                list.add(obj);
                            }
                        }
                        return list;
                    }
                    //map
                    case LEFT_BRACE: {
                        Map map = createEmptyMap();
                        Object key;
                        Object val;
                        while ((key = read(in, charset)) != close) {
                            while ((b = in.read()) != COLON) {
                                if (b == EOF) {
                                    throw new IOException("EOF");
                                }
                            }
                            val = read(in, charset);
                            if (map.containsKey(key)) {
                                Object prev = map.get(key);
                                DuplicatedKeyList list;
                                if (prev instanceof DuplicatedKeyList) {
                                    list = (DuplicatedKeyList) prev;
                                    //((DuplicatedKeyList) prev).add(val);
                                } else {
                                    list = new DuplicatedKeyList(new ArrayList());
                                    list.add(prev);
                                }
                                list.add(val);
                                map.put(key, list);
                                //}
                                System.err.println("WARNING: duplicated key: " + key);
                            } else {
                                if (val instanceof Finish) {
                                    val = ((Finish) val).val;
                                    map.put(key, val);
                                    break;
                                } else {
                                    map.put(key, val);
                                }
                            }
                        }
                        return map;
                    }
                    //string
                    case STRING: {
                        buf.reset();
                        int a = 0;
                        while ((b = in.read()) != STRING || a == BS) {
                            buf.write(b);
                            a = b;
                        }
                        return unescape(buf.toString(charset.name()));
                    }
                    case TRUE_UPPER: {
                    }
                    //true
                    case TRUE: {
                        in.skip(4);
                        return true;
                    }
                    //false
                    case FALSE_UPPER: {
                    }
                    case FALSE: {
                        in.skip(5);
                        return false;
                    }
                    //null
                    case NULL_UPPER: {
                    }
                    case NULL_LOWER: {
                        in.skip(4);
                        return null;
                    }
                    //map right brackets
                    case RIGHT_BRACE: {
                    }
                    case RIGHT_BRACKET: {
                        return close;
                    }
                    //number
                    default: {
                        buf.reset();
                        buf.write(b);
                        while ((b = in.read()) != EOF) {
                            if (isRegular(b)) {
                                buf.write(b);
                            } else {
                                break;
                            }
                        }
                        String str = buf.toString(charset.name());
                        Number num;
                        if (str.indexOf('.') != -1) {
                            num = Double.valueOf(str);
                        } else {
                            num = Long.valueOf(str);
                        }
                        if (b == RIGHT_BRACKET || b == RIGHT_BRACE) {
                            return new Finish(num);
                        }
                        return num;
                    }
                }
            }

        }
        return close;
    }

    private void writeMulti(PrintStream out, Object key, Collection value, boolean format, int depth) throws IOException {
        Iterator it = value.iterator();
        while (it.hasNext()) {
            if (format) {
                writeBreak(out, depth + writeSpaceCount);
            }
            write(out, key, format, depth + writeSpaceCount);
            out.write(COLON);
            if (format) {
                writeSpace(out, writeSpaceCount);
            }
            write(out, it.next(), format, depth + writeSpaceCount);
            if (it.hasNext()) {
                out.write(COMMA);
            }
        }

    }

    /**
     * Returns {@code true} if the specified {@code b} byte is regular
     * character, otherwise {@code false}.
     *
     * @param b the specified byte
     * @return {@code true} if the specified {@code b} byte is regular
     * character, otherwise {@code false}.
     */
    private boolean isRegular(int b) {
        return b > 32
                && b != LEFT_BRACKET
                && b != LEFT_BRACE
                && b != COMMA
                && b != RIGHT_BRACKET
                && b != RIGHT_BRACE;
    }

    /**
     * Returns the unescaped string.
     *
     * @param str the input source
     * @return the unescaped string.
     */
    private String unescape(String str) {
        str = str.replace("\\b", "\b");
        str = str.replace("\\f", "\f");
        str = str.replace("\\n", "\n");
        str = str.replace("\\r", "\r");
        str = str.replace("\\t", "\t");
        str = str.replace("\\\"", "\"");
        return str;
    }

    /**
     * Returns the escaped string.
     *
     * @param str the input source
     * @return the escaped string.
     */
    public static String escape(String str) {
        str = str.replace("\b", "\\b");
        str = str.replace("\f", "\\f");
        str = str.replace("\n", "\\n");
        str = str.replace("\r", "\\r");
        str = str.replace("\t", "\\t");
        str = str.replace("\"", "\\\"");
        return str;
    }

    /**
     * Writes spaces to a specified output {@code out}.
     *
     * @param out the specified output
     * @param spaceCount the spaces count
     * @throws IOException if IO Error Occurs.
     */
    private void writeSpace(OutputStream out, int spaceCount) throws IOException {
        byte[] b = new byte[spaceCount];
        for (int i = 0; i < b.length; i++) {
            b[i] = SP;
        }
        out.write(b);
    }

    /**
     * Writes break line and spaces to a specified output {@code out}.
     *
     * @param out the specified output
     * @param spaceCount the spaces count
     * @throws IOException if IO Error Occurs.
     */
    private void writeBreak(OutputStream out, int spaceCount) throws IOException {
        out.write(EOL);
        writeSpace(out, spaceCount);
    }

    /**
     * Creates a new instance of JSON.
     *
     * @return a new instance of JSON.
     */
    public static Json getInstance() {
        return new Json();
    }

    public Object read(byte[] b) throws IOException {
        return read(new ByteArrayInputStream(b));
    }

    /**
     * This class can contains json elements to one key. json objects (map) can
     * contains duplicate values to one key.
     */
    public static class DuplicatedKeyList extends AbstractList {

        private List list;

        public DuplicatedKeyList(List list) {
            if (list == null) {
                throw new NullPointerException("list is null");
            }
            this.list = list;
        }

        @Override
        public void add(int index, Object element) {
            list.add(index, element);
        }

        @Override
        public Object set(int index, Object element) {
            return list.set(index, element);
        }

        @Override
        public Object remove(int index) {
            return list.remove(index);
        }

        @Override
        public Object get(int index) {
            return list.get(index);
        }

        @Override
        public int size() {
            return list.size();
        }

        @Override
        public String toString() {
            Iterator it = iterator();
            if (!it.hasNext()) {
                return "[]";
            }
            StringBuilder sb = new StringBuilder();
            sb.append('[');
            for (;;) {
                sb.append('@').append('=');
                Object e = it.next();
                sb.append(e == this ? "(this Collection)" : e);
                if (!it.hasNext()) {
                    return sb.append(']').toString();
                }
                sb.append(',').append(' ');
            }
        }
    }

    /**
     * This class is a marker class which must use if the json collection (map
     * or list) will be finished.
     */
    class Finish {

        /**
         * the last object
         */
        private Object val;

        /**
         * Creates a new instance with the specified {@code val} value.
         *
         * @param val the specified value
         */
        public Finish(Object val) {
            this.val = val;
        }

    }

}