How to convert XML to JSON in ASP.NET C#

Please read the comments for suggestions on improvements to the code.

Introduction

JSON is a lightweight data-interchange format. It is particularly useful because it can be 'decoded' easily by web page JavaScript into object form.

AJAX-based web pages use XmlHttpRequest to receive data from a server in response to a user action. While the returned data is normally in XML format, it can also be returned in JSON string format and processed more easily in JavaScript.

Many applications may store information in XML format. However they may want to send data to a client using JSON. To achieve this, they must convert their XML data into JSON format. The ASP.NET C# code below does this job.

Code Description

• The code never generates number or boolean values.
• The XML documentElement is always reported as member:object even if it could be shortened by the following rules.
• Element attributes are converted into member "attr_name":"attr_value".

  XML	JSON
  <xx yy='nn'></xx>	{ "xx": {"yy":"nn"} }
  <xx yy=''></xx>	{ "xx": {"yy":""} }

• Element children with no attributes, children or text are converted into member "child_name":null

  XML	JSON
  <xx/>	{ "xx":null }

• Element children with no attributes or children but contain text are converted into "child_name":"child_text"

  XML	JSON
  <xx>yyy</xx>	{ "xx":"yyy" }

• Other element attributes and children are converted into "child_name":object or an array "child_name":[elements] as appropriate, with element text converted into a member with name "value"

  XML	JSON
  <xx yy='nn'><mm>zzz</mm></xx>	{ "xx": {"yy":"nn", "mm":"zzz"} }
  <xx yy='nn'><mm>zzz</mm><mm>aaa</mm></xx>	{ "xx": {"yy":"nn", "mm": [ "zzz", "aaa" ] } }
  <xx><mm>zzz</mm>some text</xx>	{ "xx": {"mm":"zzz", "value":"some text"} }
  <xx value='yyy'>some text<mm>zzz</mm>more text</xx>	{ "xx": {"mm":"zzz", "value": [ "yyy", "some text", "more text" ] } }

• Characters are made safe for conversion into JSON. Note that this does not protect your JavaScript from attack if any of the source XML comes from an unsafe source, eg user input.

  XML	JSON
  <aa>/z'z"z\yyy<aa><	{"aa": "\/z\u0027z\"z\\yyy" }

In some special circumstances, such as in the example below, you may need to escape the backslash characters again, eg:

Note that there may be security implications for web pages using unchecked XML contents.

Example

XML Input:

<space name="Cake Collage">
<frame>
  <photo img="cakecollage1.jpg" />
  <text string="Browse my cake space" />
  <rule type="F" img="cakecollage9.jpg" x="150" y="0" w="300" h="250" />
  <rule type="F" img="cakecollage2.jpg" x="0" y="0" w="150" h="220" />
</frame>
<frame>
  <photo img="cakecollage2.jpg" />
  <rule type="B" img="cakecollage1.jpg" />
  <rule type="L" img="cakecollage3.jpg" />
</frame>
</space>

JSON Output (re-formatted):

{ "space":
  { "name": "Cake Collage",
    "frame": [ {"photo": { "img": "cakecollage1.jpg" },
                "rule": [ { "type": "F",
                            "img": "cakecollage9.jpg",
                            "x": "150",
                            "y": "0",
                            "w": "300",
                            "h": "250"
                          }, 
                          { "type": "F",
                            "img": "cakecollage2.jpg",
                            "x": "0",  
                            "y": "0",  
                            "w": "150",  
                            "h": "220" 
                          }
                        ],
                "text": { "string": "Browse my cake space" }
               },
               {"photo": { "img": "cakecollage2.jpg" },
                "rule": [ { "type": "B", "img": "cakecollage1.jpg" },
                          { "type": "L",  "img": "cakecollage3.jpg" }
                        ]
               }
             ]
  }
}

Once the JSON has been converted into a JavaScript object, eg called space_DOM, the following objects are available:

• space_DOM.space.name
• space_DOM.space.frame.length
• space_DOM.space.frame[0].text.string
• space_DOM.space.frame[0].rule[0].type

Your JavaScript code should be flexible to cope with members not existing, members existing as a single value, or members existing as an array. I find it useful to have a JavaScript function ObjectToArray which converts all these cases into an Array of length 0, 1 or greater.

function ObjectToArray( obj)
{
    if( !obj) return new Array();
    if( !obj.length) return new Array(obj);
    return obj;
}

space_DOM.space.frame = ObjectToArray(space_DOM.space.frame);

XmlToJSON C# code

private static string XmlToJSON(XmlDocument xmlDoc)
{
    StringBuilder sbJSON = new StringBuilder();
    sbJSON.Append("{ ");
    XmlToJSONnode(sbJSON, xmlDoc.DocumentElement, true);
    sbJSON.Append("}");
    return sbJSON.ToString();
}

//  XmlToJSONnode:  Output an XmlElement, possibly as part of a higher array
private static void XmlToJSONnode(StringBuilder sbJSON, XmlElement node, bool showNodeName)
{
    if (showNodeName)
        sbJSON.Append("\"" + SafeJSON(node.Name) + "\": ");
    sbJSON.Append("{");
    // Build a sorted list of key-value pairs
    //  where   key is case-sensitive nodeName
    //          value is an ArrayList of string or XmlElement
    //  so that we know whether the nodeName is an array or not.
    SortedList childNodeNames = new SortedList();

    //  Add in all node attributes
    if( node.Attributes!=null)
        foreach (XmlAttribute attr in node.Attributes)
            StoreChildNode(childNodeNames,attr.Name,attr.InnerText);

    //  Add in all nodes
    foreach (XmlNode cnode in node.ChildNodes)
    {
        if (cnode is XmlText)
            StoreChildNode(childNodeNames, "value", cnode.InnerText);
        else if (cnode is XmlElement)
            StoreChildNode(childNodeNames, cnode.Name, cnode);
    }

    // Now output all stored info
    foreach (string childname in childNodeNames.Keys)
    {
        ArrayList alChild = (ArrayList)childNodeNames[childname];
        if (alChild.Count == 1)
            OutputNode(childname, alChild[0], sbJSON, true);
        else
        {
            sbJSON.Append(" \"" + SafeJSON(childname) + "\": [ ");
            foreach (object Child in alChild)
                OutputNode(childname, Child, sbJSON, false);
            sbJSON.Remove(sbJSON.Length - 2, 2);
            sbJSON.Append(" ], ");
        }
    }
    sbJSON.Remove(sbJSON.Length - 2, 2);
    sbJSON.Append(" }");
}

//  StoreChildNode: Store data associated with each nodeName
//                  so that we know whether the nodeName is an array or not.
private static void StoreChildNode(SortedList childNodeNames, string nodeName, object nodeValue)
{
	// Pre-process contraction of XmlElement-s
    if (nodeValue is XmlElement)
    {
        // Convert  <aa></aa> into "aa":null
        //          <aa>xx</aa> into "aa":"xx"
        XmlNode cnode = (XmlNode)nodeValue;
        if( cnode.Attributes.Count == 0)
        {
            XmlNodeList children = cnode.ChildNodes;
            if( children.Count==0)
                nodeValue = null;
            else if (children.Count == 1 && (children[0] is XmlText))
                nodeValue = ((XmlText)(children[0])).InnerText;
        }
    }
    // Add nodeValue to ArrayList associated with each nodeName
    // If nodeName doesn't exist then add it
    object oValuesAL = childNodeNames[nodeName];
    ArrayList ValuesAL;
    if (oValuesAL == null)
    {
        ValuesAL = new ArrayList();
        childNodeNames[nodeName] = ValuesAL;
    }
    else
        ValuesAL = (ArrayList)oValuesAL;
    ValuesAL.Add(nodeValue);
}

private static void OutputNode(string childname, object alChild, StringBuilder sbJSON, bool showNodeName)
{
    if (alChild == null)
    {
        if (showNodeName)
            sbJSON.Append("\"" + SafeJSON(childname) + "\": ");
        sbJSON.Append("null");
    }
    else if (alChild is string)
    {
        if (showNodeName)
            sbJSON.Append("\"" + SafeJSON(childname) + "\": ");
        string sChild = (string)alChild;
        sChild = sChild.Trim();
        sbJSON.Append("\"" + SafeJSON(sChild) + "\"");
    }
    else
        XmlToJSONnode(sbJSON, (XmlElement)alChild, showNodeName);
    sbJSON.Append(", ");
}

// Make a string safe for JSON
private static string SafeJSON(string sIn)
{
    StringBuilder sbOut = new StringBuilder(sIn.Length);
    foreach (char ch in sIn)
    {
        if (Char.IsControl(ch) || ch == '\'')
        {
            int ich = (int)ch;
            sbOut.Append(@"\u" + ich.ToString("x4"));
            continue;
        }
        else if (ch == '\"' || ch == '\\' || ch == '/')
        {
            sbOut.Append('\\');
        }
        sbOut.Append(ch);
    }
    return sbOut.ToString();
}

Using XmlToJSON

The following code shows how to use XmlToJSON() when an ASP.NET 2 page loads. It then uses the ASP.NET2 ClientScriptManager to insert code containing the JSON string into the web page. See the following section for an example of JavaScript space_processJSON().

protected void Page_Load(object sender, EventArgs e)
{
    XmlDocument doc = new XmlDocument();
    try
    {
        string path = Server.MapPath(".");
        doc.Load(path+"whatever.xml");
    }
    catch (Exception ex)
    {
        lblError.Text = ex.ToString();
        return;
    }

    // Convert XML to a JSON string
    string JSON = XmlToJSON(doc);
    
    // Replace \ with \\ because string is being decoded twice
    JSON = JSON.Replace(@"\", @"\\");
    
    // Insert code to process JSON at end of page
    ClientScriptManager cs = Page.ClientScript;
    cs.RegisterStartupScript(GetType(), "SpaceJSON", "space_processJSON('" + JSON + "');", true);
}

Client-side code

<script src="space/json.js" type="text/javascript"></script>

<script type="text/javascript">
function space_processJSON( JSON)
{
    space_DOM = JSON.parseJSON();
    if( !space_DOM)
    {
        alert("JSON decode error");
        return;
    }
    space_DOM.space.frame = ObjectToArray(space_DOM.space.frame);
    space_frameCount = space_DOM.space.frame.length;
    .. or whatever
}
</script>

Comments:

Michael, Mon, 19 Jun 2006 16:46:05 (GMT)

See this implementation: http://groups.google.de/group/ajaxpro/browse_thread/thread/219f830011e5ca6f/9e72c85fcf802a84#9e72c85fcf802a84

Damon Carr, Thu, 07 Sep 2006 12:24:31 (GMT)

Excellent work.

Alex Egg, Sun, 31 Dec 2006 06:31:43 (GMT)

Question: Why is XmlToJSON private? Wouldn't it be more appropriate for this method to be declared as public? Also, I think you should change the XmlDocument parameter of XmlToJSON to an XmlNode, it would be much more versatile.
Also, I have discovered you code does not produce correct JSON when the xml contains cdata blocks

Eric Walker, Mon, 8 Oct 2007 08:01:45 -0700

I found that an empty xml node was not being decoded properly (an extra } was being added). So for example <foo /> would be translated as {"foo" : }}
By tracking whether or not a child was added, I was able to work arround this issue:

//  XmlToJSONnode:  Output an XmlElement, possibly as part of a higher array
        public static void XmlToJSONnode(StringBuilder sbJSON, XmlElement node, bool showNodeName)
        {
            bool childAdded = false;
            if (showNodeName)
                sbJSON.Append("\"" + SafeJSON(node.Name) + "\": ");
            sbJSON.Append("{");
            // Build a sorted list of key-value pairs
            //  where   key is case-sensitive nodeName
            //          value is an ArrayList of string or XmlElement
            //  so that we know whether the nodeName is an array or not.
            SortedList childNodeNames = new SortedList();

            //  Add in all node attributes
            if (node.Attributes != null)
                foreach (XmlAttribute attr in node.Attributes)
                    StoreChildNode(childNodeNames, attr.Name, attr.InnerText);

            //  Add in all nodes
            foreach (XmlNode cnode in node.ChildNodes)
            {
                childAdded = true;
                if (cnode is XmlText)
                    StoreChildNode(childNodeNames, "value", cnode.InnerText);
                else if (cnode is XmlElement)
                    StoreChildNode(childNodeNames, cnode.Name, cnode);
            }

            // Now output all stored info
            foreach (string childname in childNodeNames.Keys)
            {
                childAdded = true;
                ArrayList alChild = (ArrayList)childNodeNames[childname];
                if (alChild.Count == 1)
                    OutputNode(childname, alChild[0], sbJSON, true);
                else
                {
                    sbJSON.Append(" \"" + SafeJSON(childname) + "\": [ ");
                    foreach (object Child in alChild)
                        OutputNode(childname, Child, sbJSON, false);
                    sbJSON.Remove(sbJSON.Length - 2, 2);
                    sbJSON.Append(" ], ");
                }
            }
            sbJSON.Remove(sbJSON.Length - 2, 2);
            if (childAdded)
            {
                sbJSON.Append(" }");
            }
            else
            {
                sbJSON.Append(" null");
            }
        }

I hope this is helpful.

Leon, Mon, 22 Oct 2007 09:20:55 -0700

Another way to do it (DataContractJsonSerializer):
http://blogs.msdn.com/kaevans/archive/2007/09/04/use-linq-and-net-3-5-to-convert-rss-to-json.aspx

Mark Brito, Tue, 19 Feb 2008 21:16:32 GMT

In spirit of helping .. I found a bug where there is only one element in the xml, it would make it a single element instead of an array.. simply change the following line of code..

if (alChild.Count == 1)

to

if (alChild.Count == 1 && (alChild[0] is string))

Below is the entire function.

public static void XmlToJSONnode(StringBuilder sbJSON, XmlElement node, bool showNodeName)
{
    bool childAdded = false;
    if (showNodeName)
        sbJSON.Append("\"" + SafeJSON(node.Name) + "\": ");
    sbJSON.Append("{");
    // Build a sorted list of key-value pairs
    //  where   key is case-sensitive nodeName
    //          value is an ArrayList of string or XmlElement
    //  so that we know whether the nodeName is an array or not.
    SortedList childNodeNames = new SortedList();

    //  Add in all node attributes
    if (node.Attributes != null)
        foreach (XmlAttribute attr in node.Attributes)
            StoreChildNode(childNodeNames, attr.Name, attr.InnerText);

    //  Add in all nodes
    foreach (XmlNode cnode in node.ChildNodes)
    {
        childAdded = true;
        if (cnode is XmlText)
            StoreChildNode(childNodeNames, "value", cnode.InnerText);
        else if (cnode is XmlElement)
            StoreChildNode(childNodeNames, cnode.Name, cnode);
    }

    // Now output all stored info
    foreach (string childname in childNodeNames.Keys)
    {
        childAdded = true;
        ArrayList alChild = (ArrayList)childNodeNames[childname];
        bool bFlag = false;
        foreach (object oChild in alChild) bFlag = true;
        if (alChild.Count == 1 && (alChild[0] is string))
            OutputNode(childname, alChild[0], sbJSON, true);
        else
        {
            sbJSON.Append(" \"" + SafeJSON(childname) + "\": [ ");
            foreach (object Child in alChild)
                OutputNode(childname, Child, sbJSON, false);
            sbJSON.Remove(sbJSON.Length - 2, 2);
            sbJSON.Append(" ], ");
        }
    }
    sbJSON.Remove(sbJSON.Length - 2, 2);
    if (childAdded)
    {
        sbJSON.Append(" }");
    }
    else
    {
        sbJSON.Append(" null");
    }
}

Milind Amin, Fri, 25 Jul 2008 06:52:56 GMT

Thanks. Very Good Article.

Paul Chu, Thu, 16 Oct 2008 01:52:44 GMT

Thank you and all the other contributors for this excellent article.
Does the last post contain all the suggested enhancements ?
Answer: I haven't tested the suggestions but they look good!

Chris, Thu, 13 Nov 2008 04:47:25 GMT

I could see where this would come in handy. Hats off to you for that. Overall, I would prefer to build JSON from real objects which gives me the ability to serialize to XML, JSON, or whatever.

noone, Mon, 06 Apr 2009 12:55:55 GMT

Use the .NET 3.5 JavaScript Serializer: System.Web.Script.Serialization.JavaScriptSerializer

Michele Costabile, Wed, 20 May 2009 13:33:31 GMT

I had a problem with an extra brace at the end of the file. I solved it checking that I really had to remove two characters from the end of the string buffer in XmlToJSONnode. The following is my version of the function. Maybe further inspection of the code would be in order for finding a more elegant solution, but this is what I managed to do in a short time.

//  XmlToJSONnode:  Output an XmlElement, possibly as part of a higher array
private static void XmlToJSONnode(StringBuilder sbJSON, XmlElement node, bool showNodeName)
{
    if (showNodeName)
        sbJSON.Append("\"" + SafeJSON(node.Name) + "\": ");
    sbJSON.Append("{");
    // Build a sorted list of key-value pairs
    //  where   key is case-sensitive nodeName
    //          value is an ArrayList of string or XmlElement
    //  so that we know whether the nodeName is an array or not.
    SortedList childNodeNames = new SortedList();

    //  Add in all node attributes
    if (node.Attributes != null)
        foreach (XmlAttribute attr in node.Attributes)
            StoreChildNode(childNodeNames, attr.Name, attr.InnerText);

    //  Add in all nodes
    foreach (XmlNode cnode in node.ChildNodes)
    {
        if (cnode is XmlText)
            StoreChildNode(childNodeNames, "value", cnode.InnerText);
        else if (cnode is XmlElement)
            StoreChildNode(childNodeNames, cnode.Name, cnode);
    }

    // Now output all stored info
    bool hasAddedChild = false;
    foreach (string childname in childNodeNames.Keys)
    {
        ArrayList alChild = (ArrayList)childNodeNames[childname];
        if (alChild.Count == 1 && (alChild[0] is string))
        {
            hasAddedChild = true;
            OutputNode(childname, alChild[0], sbJSON, true);
        }
        else
        {
            sbJSON.Append(" \"" + SafeJSON(childname) + "\": [ ");
            foreach (object Child in alChild)
            {
                hasAddedChild = true;
                OutputNode(childname, Child, sbJSON, false);
            }
            if (hasAddedChild)
                sbJSON.Remove(sbJSON.Length - 2, 2);
            sbJSON.Append(" ], ");
        }
    }
    if (hasAddedChild)
        sbJSON.Remove(sbJSON.Length - 2, 2);
    sbJSON.Append(" }");
}

Overide, Thu, 09 Jul 2009 11:09:49 GMT

ObjectToArray(obj): function is incorrect if obj is String. Maybe better:

function ObjectToArray( obj)
{
    if (!obj) return new Array();
    if (!(obj instanceof Array)) return new Array(obj);
    return obj;
}

Override, Fri, 10 Jul 2009 08:39:11 GMT

and also it conflicts with JQuery. Line: v = f(v); - not enough memory

lucky, Fri, 21 Aug 2009 01:29:39 GMT

Thank

Karl, Thu, 15 Oct 2009 23:46:49 GMT

I added a check for numeric values, to optionally display the quotes.
In OutputNode() change the one line with the quotes to:

Double temp;
if (Double.TryParse(sChild, out temp))
 sbJSON.Append(SafeJSON(sChild));
else
 sbJSON.Append("\"" + SafeJSON(sChild) + "\"");

Richard, Mon, 02 Aug 2010 16:59:07 GMT

I've got an bug with the code - It doesn't handle unicode characters! An Ampersand would be return as an '&' rather than '&amp;'. This is presumably due to the use of InnerXml rather than InnerText. However using InnerXml causes my JSON to be incorrectly rendered.
Any thoughts?

leonwoo, Thu, 14 Oct 2010 01:01:25 GMT

Nice code but has a bug with the comma in certain scenario. The workaround I put is this at the end of the OutputNode function.

string temp2 = sbJSON.ToString().Trim();
if(temp2.Substring(temp2.Length - 1) != ",")
	sbJSON.Append(", ");

Gregory, Thu, 03 Mar 2011 16:03:27 GMT

Have not tested validity of the output for my needs, but comparing this methodology to the other libraries out there, I am quite impressed. I was getting logarithmic times with other JSON to XML libraries out there. As I have a huge file to deal with, the results with the others were unacceptable.

Matt, Tue, 10 Jan 2012 17:10:56 GMT

FYI adding in CDATA handling is easy. Change the "Add in all nodes" loop to this:

//  Add in all nodes
foreach (XmlNode cnode in node.ChildNodes)
{
    childAdded = true;
    if (cnode.ChildNodes[0] is XmlCDataSection)
        StoreChildNode(childNodeNames, cnode.Name, cnode.ChildNodes[0].InnerText);
    else if (cnode is XmlText)
        StoreChildNode(childNodeNames, "value", cnode.InnerText);
    else if (cnode is XmlElement)
        StoreChildNode(childNodeNames, cnode.Name, cnode);
}

sarvesh, Fri, 12 Apr 2013 04:08:30 GMT

awesome post... and can you pls help me for getting the things done from JASON string to XML? plss...
Thank you in advance.