Empty Json Array is obtained while converting from String to Json Array in Java

Question

I am trying to convert a String to Json Array (without name/tag) and iterate through the resultant array.. But the resultant json array is shown as null when I debug the code. I cant find the cause of this issue.

Below is the given string that I am trying to parse into a Json Array.

String jsonString="[ {"
            + "\"TimeStamp\": \"20:10\","
            + "\"PipeTemp\": \"31.5\","
            + "\"ChocolateMixingTemp\": \"25\","
            + "\"WaterCoolingTemp\": \"5\","
            + "\"WaterMixingTemp\": \"0\","
            + "\"WaterHeatingTemp\": \"0\",},
            +{"
            + "\"TimeStamp\": \"20:00\","
            + "\"PipeTemp\": \"35.5\","
            + "\"ChocolateMixingTemp\": \"28\","
            + "\"WaterCoolingTemp\": \"3\","
            + "\"WaterMixingTemp\": \"15\","
            + "\"WaterHeatingTemp\": \"0\","
            +}]";

I pass the above string to Java Array instance and then iterate it using for loop to generate a PDF Table. But I see that Json Array is shown as null when I try to check its size.

JSONArray jsonArray = new JSONArray(jsonString);

 JSONObject jsonObject;
 for(int n = 0; n < jsonArray.length(); n++)
{
 table.addCell(createCell( (String) jsonObject.get("TimeStamp"),Element.ALIGN_CENTER)); 
             table.addCell(createCell( (String) jsonObject.get("PipeTemp"),Element.ALIGN_CENTER)); 
             table.addCell(createCell( (String) jsonObject.get("ChocolateMixingTemp"), Element.ALIGN_CENTER)); 
             table.addCell(createCell( (String) jsonObject.get("WaterCoolingTemp"),Element.ALIGN_CENTER)); 
             table.addCell(createCell( (String) jsonObject.get("WaterMixingTemp"),Element.ALIGN_CENTER)); 
jsonObject.get("WaterHeatingTemp"),Element.ALIGN_CENTER)); 

}

Can someone please help me identify why the array is shown as empty? I also tried to test with a simple string containing of only two key-value pairs. But got the same result.

Your Json could be a problem, there is a additional comma (,) + "\"WaterHeatingTemp\": \"0\", >> It should be with out comma(,) "\"WaterHeatingTemp\": \"0\" — Rowi
– Rowi, Commented Jul 11, 2019 at 7:46
There are definitely some typos in the Json, it won't compile for me. — Amongalen
– Amongalen, Commented Jul 11, 2019 at 7:51
It's easily seen with this syntax highlighting of Stackoverflow. You immediately see that there's a problem somewhere near WaterHeatingTemp. — MC Emperor
– MC Emperor, Commented Jul 11, 2019 at 10:02

Anatoly Samoylenko · Accepted Answer · 2019-07-11 07:55:21Z

Your code is wrong. Try this code to test the JSON array:

String jsonString = "[ {"
            + "\"TimeStamp\": \"20:10\","
            + "\"PipeTemp\": \"31.5\","
            + "\"ChocolateMixingTemp\": \"25\","
            + "\"WaterCoolingTemp\": \"5\","
            + "\"WaterMixingTemp\": \"0\","
            + "\"WaterHeatingTemp\": \"0\",},"
            + "{"
            + "\"TimeStamp\": \"20:00\","
            + "\"PipeTemp\": \"35.5\","
            + "\"ChocolateMixingTemp\": \"28\","
            + "\"WaterCoolingTemp\": \"3\","
            + "\"WaterMixingTemp\": \"15\","
            + "\"WaterHeatingTemp\": \"0\","
            + "}]";

JSONArray jsonArray = new JSONArray(jsonString);

System.out.println(jsonArray);

for (int n = 0; n < jsonArray.length(); n++) {
    JSONObject jsonObject = jsonArray.getJSONObject(n);
    System.out.println((String) jsonObject.get("TimeStamp"));
}

Nitin · Accepted Answer · 2019-07-11 08:12:04Z

First, your json string is not properly formatted, please see below one formatted:

String s="[ {"
                + "\"TimeStamp\": \"20:10\","
                + "\"PipeTemp\": \"31.5\","
                + "\"ChocolateMixingTemp\": \"25\","
                + "\"WaterCoolingTemp\": \"5\","
                + "\"WaterMixingTemp\": \"0\","
                + "\"WaterHeatingTemp\": \"0\",},"
                + "{"
                + "\"TimeStamp\": \"20:00\","
                + "\"PipeTemp\": \"35.5\","
                + "\"ChocolateMixingTemp\": \"28\","
                + "\"WaterCoolingTemp\": \"3\","
                + "\"WaterMixingTemp\": \"15\","
                + "\"WaterHeatingTemp\": \"0\","
                + "}]";

Second, I don't see your jsonObject getting initialized with anything. If you want to use values from json use jsonArray.get(index) method.

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