JSON error with square brackets

Question

I have XML file looking like this

<Reading>
<Item Month="_October.xml">
    <kWhReading Firstday="1" />
    <kWhReading Lastday="552" />
</Item>
</Reading>

Then using this line of code

JSONArray jsonArray = (JSONArray) JSONSerializer.toJSON( json.toString() );

I got this

[{"@Month":"_October.xml","kWhReading":[{"@Firstday":"1"},{"@Lastday":"552"}]}]

Then, using this

JSONObject jsonobject = (JSONObject) jsonArray.get(0);

I got this

{"@Month":"_October.xml","kWhReading":[{"@Firstday":"1"},{"@Lastday":"552"}]}

Now the problem is, I want to get the value of Lastday from kWhReading using

JSONObject readingkWhLast = jsonobject.getJSONObject("kWhReading");

but it doesn't work and it threw exception

net.sf.json.JSONException: JSONObject["kWhReading"] is not a JSONObject.
at net.sf.json.JSONObject.getJSONObject(JSONObject.java:2058)
at com.syntronic.bean.RecentUsage.doPost(RecentUsage.java:82)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:931)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

I am pretty sure it has to do with the square brackets that enclosed Firstday and Lastday but I am not sure how to remove that. Anyone can help me here?

Answer 1

Never used the JSON library, but this should be on the right track

JSONObject readingkWhLast = jsonobject.getJSONArray("kWhReading").get(1);

From your jsonobject retrieve the JSONArray named "kWhReading" and then retrieve the element at offset 1 (the second object).

This is all in the API documentation. You really should step back and read the docs thoroughly so you understand the capabilities of the library.

Answer 2

Once you get jsonArray:

[{"@Month":"_October.xml","kWhReading":[{"@Firstday":"1"},{"@Lastday":"552"}]}]

Then, you need to use getJSONObject() with an index number to get an element within that array. The second one is "kWhReading", so:

JSONObject kWhReadObject = jsonArray.getJSONObject(1);

That should put you here:

{"kWhReading":[{"@Firstday":"1"},{"@Lastday":"552"}]}

To get the value of kWhReading (which is itself an array):

JSONArray kWhReadArray = kWhReadObject.getJSONArray("kWhReading");

Now you're here:

[{"@Firstday":"1"},{"@Lastday":"552"}]

Back to index numbers. Again, you want the second one:

JSONObject lastDayObj = kWhReadArray.getJSONObject(1);

And finally:

String lastDay = lastDayObj.getString("@Lastday");

The docs are here: http://json-lib.sourceforge.net/apidocs/net/sf/json/JSONArray.html