How can I get a Javascript variable value in Java?

Question

In my current project I have to read a JavaScript file from the web and extract an object from it. The variable can vary from time to time, so I have to read it instead of hard coding it into my android app.

Say I want to extract the following variable (and parse the string using JSONObject after that, which is trivial):

var abc.xyz = {
"a": {"one", "two", "three"},
"b": {"four", "five"}
}

I have a problem with this. Do I have to implement some compiler-like scanner just to look for the name and get its value, or there is some existing tool I can use?

The JavaScript file is not as simple as this example. It contains a lot of other code. So a simple new JSONObject() or something will not do.

A much better way would be to store the data in JSON format on the server. Loading of JSON data is in the JavaScript/web browser as simple as in Java. — Robert
– Robert, Commented Nov 5, 2012 at 13:16
@Cthulhu nice suggestion, but it crashes since the js is for browser — onemach
– onemach, Commented Nov 6, 2012 at 8:37

epascarello · Accepted Answer · 2012-11-05 13:57:43Z

1

There are many libraries in Java to parse the JSON. There is a list on JSON.org

Read the file with Java

import org.json.JSONObject;

URL url = new URL("http://example.com/foo.js");
InputStream urlInputStream = url.openStream();
JSONObject json = new JSONObject(urlInputStream.toString());

edited Nov 5, 2012 at 13:57

answered Nov 5, 2012 at 13:20

epascarello

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2 Comments

onemach Over a year ago

I know how to parse it. I am asking how to get it.

epascarello Over a year ago

Make a http request, your question says nothing about reading it. lol

onemach · Accepted Answer · 2012-11-06 08:30:39Z

Finally code it myself.

//remove comments
private String removeComment(String html){
    String commentA = "/*";
    String commentB = "*/";
    int indexA, indexB;
    indexA = html.indexOf(commentA);
    indexB = html.indexOf(commentB);
    while(indexA != -1 && indexB != -1 ){
        html = html.substring(0, indexA) + html.substring(indexB + commentB.length());
        indexA = html.indexOf(commentA);
        indexB = html.indexOf(commentB);
    }
    return html;
}

    //find variable with name varName
private String findVar(String varName, String html, char lBrace, char rBrace){
    String tmp = html.substring(html.indexOf(varName));
    tmp = tmp.substring(tmp.indexOf(lBrace));

    int braceCount = 0;
    int index = 0;
    while(true){
        if(tmp.charAt(index) == lBrace){
            braceCount ++;
        }else if(tmp.charAt(index) == rBrace){
            braceCount --;
        }
        index ++;
        if(braceCount == 0){
            break;
        }
    }
    return tmp.substring(0, index);
}

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