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| Java compute node: Extracting data from Json Array |
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Message
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| raghuiib |
 Posted: Sat Oct 27, 2018 10:09 am Post subject: Java compute node: Extracting data from Json Array |
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Novice
Joined: 01 Oct 2018
Posts: 11
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Hello,
IIB Version: 10.0.0.13
I have few years of ESQL experience and very new to Java coding. I am running into an issue with extracting data from Json array. Very likely I am missing something in my Java code.
My input message:
| Code: |
{
"header": {
"_Message_ID": "123",
"_Type": "bravo"
},
"payload": {
"field1": "value1",
"field2": "value2",
"rulesApplied": ["R1","R2","R3"]
}
} |
Here is the message tree before code execution:
| Code: |
Message
JSON
Data
header
_Message_ID:CHARACTER:123
_Type:CHARACTER:bravo
payload
field1:CHARACTER:value1
field2:CHARACTER:value2
rulesApplied
Item:CHARACTER:R1
Item:CHARACTER:R2
Item:CHARACTER:R3 |
Java code:
| Code: |
PreparedStatement ps = conn.prepareStatement(sql);
MbElement refPayload = inMessage.getRootElement().getFirstElementByPath("JSON/Data/payload");
ps.setString(1,(refPayload.getFirstElementByPath("/rulesApplied/Item[1]").getValueAsString())); |
The third line of code where I reference Item[1] results in NULL pointer exception.
To access data in Json array, I referred to this IBM documentation:
https://www.ibm.com/support/knowledgecenter/en/SSMKHH_10.0.0/com.ibm.etools.mft.doc/bc28412_.htm
Hoping someone in this forum can help me with what I am missing.
Thanks. |
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| timber |
| Posted: Sat Oct 27, 2018 1:03 pm Post subject: |
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Grand Master
Joined: 25 Aug 2015
Posts: 1292
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Nothing obviously incorrect in your Java. I suggest that you follow the usual debugging techniques. Simplify the code until the location of the error becomes obvious. I would start by checking that you can access the JSON node, then the Data node.
Alternatively, you could stop trying to use the old-fashioned Java API (which isn't particularly user-friendly) and generate JAXB bindings from your schema. That will provide you with a much neater API onto the message tree. |
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| raghuiib |
| Posted: Sun Oct 28, 2018 5:58 am Post subject: |
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Novice
Joined: 01 Oct 2018
Posts: 11
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I am able to access other data elements, both in header and payload, that are not part of the array. It is just the array elements that is the issue.
I am new to Java and on a learning curve. Will explore JAXB. Thank you. |
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| martinb |
| Posted: Mon Oct 29, 2018 9:27 am Post subject: |
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Master
Joined: 09 Nov 2006
Posts: 210
Location: UK
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Hi
I think the problem is you're using an absolute path here
| Code: |
refPayload.getFirstElementByPath("/rulesApplied/Item[1]")
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As you are calling getFirstElementByPath() from an element part way down the tree, you need to be giving a relative Xpath path expression as the argument. I think you should be using
| Code: |
refPayload.getFirstElementByPath("rulesApplied/Item[1]")
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HTH |
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| raghuiib |
| Posted: Mon Oct 29, 2018 12:40 pm Post subject: |
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Novice
Joined: 01 Oct 2018
Posts: 11
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Hello Martin B,
I realized it and tested it with the relative path. Still got the null pointer error.
| Code: |
| ps.setString(1,(refPayload.getFirstElementByPath("rulesApplied/Item[1]").getValueAsString())); |
I have so much more appreciation for ESQL now.
[/code] |
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