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Why my list is empty when I am parsing correct json response?

I am trying to print the ids from a JSON response. But I am not able to understand why I am getting a blank list. I have verified the JSONpath (SECTIONS_IDS_JSONPATH) from the online website and it is giving me correct results.
public static void main(String[] args) {
String SECTIONS_IDS_JSONPATH = "$.[*].instructionEvents[*].sectionId";
String sectionsData = "{\"sections\":[{\"id\":\"8da1cf5d-3150-4e11-b2af-338d1df20475\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"courseCredits\":[{\"minimum\":4,\"maximum\":null,\"measure\":\"hour\",\"increment\":null}],\"academicPeriodId\":\"8b7a8e9e-5417-42a3-9c90-8d47226b5987\",\"reservedSeatsMaximum\":0,\"maxEnrollment\":0,\"hours\":[],\"sites\":[\"All Campuses\"],\"instructors\":[],\"instructionEvents\":[{\"id\":\"9d0c49e2-1579-43c3-b25a-2f85f551e62d\",\"sectionId\":\"8da1cf5d-3150-4e11-b2af-338d1df20475\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"days\":[\"monday\",\"wednesday\",\"friday\"],\"startTm\":\"2019-01-01T09:45:00-05:00\",\"endTm\":\"2024-12-01T10:45:00-05:00\",\"localizations\":[],\"instructionalMethod\":\"Lecture\"}]},{\"id\":\"ad3f63ad-e642-4938-a9fd-318afd2d1ad0\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"courseCredits\":[{\"minimum\":4,\"maximum\":null,\"measure\":\"hour\",\"increment\":null}],\"academicPeriodId\":\"8b7a8e9e-5417-42a3-9c90-8d47226b5987\",\"reservedSeatsMaximum\":0,\"maxEnrollment\":20,\"hours\":[],\"sites\":[\"All Campuses\"],\"instructors\":[{\"id\":\"c26572de-f9c8-4623-ba6a-79997b33f1c6\",\"sectionId\":\"ad3f63ad-e642-4938-a9fd-318afd2d1ad0\",\"role\":\"primary\",\"persons\":[{\"id\":\"c1b50d79-5505-4a33-9316-b4b1f52c0ca3\",\"names\":[{\"firstName\":\"BanColoFac-1\",\"lastName\":\"CTester\",\"preferred\":true}]}]}],\"instructionEvents\":[{\"id\":\"af8fb500-29f5-4451-95d5-a11215298cd4\",\"sectionId\":\"ad3f63ad-e642-4938-a9fd-318afd2d1ad0\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"days\":[\"tuesday\",\"thursday\"],\"startTm\":\"2019-01-01T10:00:00-05:00\",\"endTm\":\"2024-12-01T10:50:00-05:00\",\"localizations\":[],\"instructionalMethod\":\"Lecture\"}]},{\"id\":\"a1422391-e2b9-4bc4-907b-371fcea01d70\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"courseCredits\":[{\"minimum\":4,\"maximum\":null,\"measure\":\"hour\",\"increment\":null}],\"academicPeriodId\":\"8b7a8e9e-5417-42a3-9c90-8d47226b5987\",\"reservedSeatsMaximum\":0,\"maxEnrollment\":20,\"hours\":[],\"sites\":[\"All Campuses\"],\"instructors\":[{\"id\":\"808daae1-3ec6-47ec-9af0-5392199bdf78\",\"sectionId\":\"a1422391-e2b9-4bc4-907b-371fcea01d70\",\"role\":\"primary\",\"persons\":[{\"id\":\"793cc9b3-57c7-4a2d-8984-07a1fb6834a9\",\"names\":[{\"firstName\":\"Andrew\",\"lastName\":\"Adams\",\"preferred\":true}]}]}],\"instructionEvents\":[{\"id\":\"730b4206-684d-4413-bf20-9bec5c1dc900\",\"sectionId\":\"a1422391-e2b9-4bc4-907b-371fcea01d70\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"days\":[\"tuesday\",\"thursday\"],\"startTm\":\"2019-01-01T10:00:00-05:00\",\"endTm\":\"2024-12-01T10:50:00-05:00\",\"localizations\":[],\"instructionalMethod\":\"Lecture\"},{\"id\":\"8bc059ab-a8f8-4469-8e79-bbc71f7fa3fd\",\"sectionId\":\"a1422391-e2b9-4bc4-907b-371fcea01d70\",\"courseId\":\"e8a65581-ed1c-43f0-90a7-7b9d51b35062\",\"days\":[\"monday\",\"wednesday\",\"friday\"],\"startTm\":\"2019-05-26T09:00:00-04:00\",\"endTm\":\"2021-05-26T09:50:00-04:00\",\"localizations\":[],\"instructionalMethod\":\"Lecture\"}]}]}";
List<String> ids = JsonPath.parse(sectionsData).read(SECTIONS_IDS_JSONPATH);
System.out.println(ids);
}

Alright, since this question might get delete if nothing else ever happens I better post this as an answer.
As explained by Andreas you should use JSONPath $.*[*].instructionEvents[*].sectionId instead. Quoting fromt the comment
The syntax $.[*] is undefined, I can't find any documentation/example
doing that. The JSONPath Online Evaluator [*based on
JSONPath-Plus implemented in JavaScript] treats it as $..[*], but the Java library treats
it differently. Since the outer part of the JSON is {"sections":[ ... ]}, you have an object, so you need a property selector (.prop or
.*). Once you've selected your property (.sections, or .*
since there's only one), the property is an array, so you need an
array selector ([2] or [*]). Hence you can use $.sections[*] or
$.*[*] to match all sections.
Indeed, looking at this massive JSONPath Comparision we can see that the syntax in question is not listed for any implementation.

How to extract one boolean field from XML?

I have a model which is in XML format as shown below and I need to parse the XML and check whether my XML has internal-flag flag set as true or not. In my other models, it might be possible, that internal-flag flag is set as false. And sometimes, it is also possible that this field won't be there so by default it will be false from my code.
<?xml version="1.0"?>
<ClientMetadata
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.google.com client.xsd"
xmlns="http://www.google.com">
<client id="200" version="13">
<name>hello world</name>
<description>hello hello</description>
<organization>TESTER</organization>
<author>david</author>
<internal-flag>true</internal-flag>
<clock>
<clock>
<for>
<init>val(tmp1) = 1</init>
<clock>
<eval><![CDATA[result("," + $convert(val(tmp1)))]]></eval>
</clock>
</for>
<for>
<incr>val(tmp1) -= 1</incr>
<clock>
<eval><![CDATA[result("," + $convert(val(tmp1)))]]></eval>
</clock>
</for>
</clock>
</clock>
</client>
</ClientMetadata>
I have a POJO in which I am storing my above model -
public class ModelMetadata {
private int modelId;
private String modelValue; // this string will have my above XML data as string
// setters and getters here
}
Now what is the best way to determine whether my model has internal-flag set as true or not?
// this list will have all my Models stored
List<ModelMetadata> metadata = getModelMetadata();
for (ModelMetadata model : metadata) {
// my model will be stored in below variable in XML format
String modelValue = model.getModelValue();
// now parse modelValue variable and extract `internal-flag` field property
}
Do I need to use XML parsing for this or is there any better way to do this?
Update:-
I have started using Stax and this is what I have tried so far but not sure how can I extract that field -
InputStream is = new ByteArrayInputStream(modelValue.getBytes());
XMLStreamReader r = XMLInputFactory.newInstance().createXMLStreamReader(is);
while(r.hasNext()) {
// now what should I do here?
}

There is an easy solution using XMLBeam (Disclosure: I'm affiliated with that project), just a few lines:
public class ReadBoolean {
public interface ClientMetaData {
#XBRead("//xbdefaultns:internal-flag")
boolean hasFlag();
}
public static void main(String[] args) throws IOException {
ClientMetaData clientMetaData = new XBProjector().io().url("res://xmlWithBoolean.xml").read(ClientMetaData.class);
System.out.println("Has flag:"+clientMetaData.hasFlag());
}
}
This program prints out
Has flag:true
for your XML.

You could also do some simple string parsing, but this will only work for small cases with proper XML and if there's only a single <internal-flag> element.
This is a simple solution to your problem without using any XML parsing utilities. Other solutions may be more robust or powerful.
Find the index of the string literal <internal-flag>. If it doesn't exist, return false.
Go forward "<internal-flag>".length (15) characters. Read up to the next </internal-flag>, which should be the string true or false.
Take that string, use Boolean.parseBoolean(String) to get a boolean value.
If you want me to help you out with the code just drop a comment!

If you are willing to consider adding Groovy to your mix (e.g. see the book Making Java Groovy) then using a Groovy XMLParser and associated classes will make this simple.
If you need to stick to Java, let me put in a shameless plug for my Xen library, which mimics a lot of the "Groovy way". The answer to your question would be:
Xen doc = new XenParser().parseText(YOUR_XML_STRING);
String internalFlag = doc.getText(".client.internal-flag");
boolean isSet = "true".equals(internalFlag);
If the XML comes from a File, Stream, or URI, that can be handled too.
Caveat emptor, (even though it is free) this is a fairly new library, written solely by a random person (me), and not thoroughly tested on all the crazy XML out there. If anybody knows of a similar, more "mainstream" library I'd be very interested in hearing about it.

regarding thrift function return list

i have thrift service with a function returning list of Object ABC:
struct ABC
{
1: string user_id;
2: string foo;
3: optional list<string> data;
}
list<ABC> getABCByUser(1:required string user_id, 2:i32 limit,3:i32 pageId, 4:string lastDocID)
throws (1:InvalidRequestException ire, 2:UnavailableException ue, 3:TimedOutException te)
server side written by c++
I print out result returned by server side, data in ABC instance is NOT null in the response of getABCByUser.
How ever on client side which is written by java:
I set break point in the code generated by thrift on java side, data in ABC instance is null, other fields are not null.
it looks like a issue on the client side. Any idea how to fix this issue?
thanks in advance!

I encounter the same problem with you. I found that if delete the "optional" modifier before list, the return value will be right. But I don't know why we can't use "optional" before list.

If you think you may have found a bug, please open a JIRA ticket and add your reproducible test case. This makes it easier for others to have a look at it. Thank you!

GWT - CellTable/DataGrid Using ImageCell

I want to add an ImageCell in a CellTable. my code is the following:
Column<Message, String> myColumn = new Column<Message, String>(new ImageCell()) {
#Override
public String getValue(Message details) {
Image image = new Image (ClientResources.of().image1());
return image.getUrl();
}
};
It shows the following warnning when I run it:
[WARN] [adminportal] - Template with variable in URL attribute context: The template code generator cannot guarantee HTML-safety of the template -- please inspect manually or use SafeUri to specify arguments in a URL attribute context
My question is that how I can return the url as string value safely. I saw an example about using imagecell before and the return value is string. I cannot find it now. Could anyone tell me how to fix this.
Note: I just want to know how to fix this if I want to use imagecell in celltable and return value is string. I know how to use imageresourcecell to achieve the same goal. Also, I know I can change the type of getValue() from string to safeHtml to achieve the goal. But i am really wondering how to achieve this by using imagecell and string type of getValue() because I saw an example about this before and I tried it successfully. Just cannot remember what I did wrong here.

There's no way to fix this (remove the warning): using a String as part of a template is inherently unsafe, and GWT warns you about it. If you're absolutely certain of the safety of your values, then you can safely ignore the warnings, but they'll still be emitted.
The only way to not have those warnings is to use a SafeUri, i.e. use the SafeImagecell. It's then up to you to guarantee the safety of your URL, depending on the method you use to construct the SafeUri (have a look at UriUtils)

Saxon 8 (Java version) problem

I'll point out now, that I'm new to using saxon, and I've tried following the docs and examples in the package, but I'm just not having luck with this problem.
Basically, I'm trying to do some xml processing in java using saxon v8. In order to get something working, I took one of the sample files included in the package and modified to my needs. It works so long as I'm not using namespaces, and that is my question. How can I get around the namespace problem? I don't really care to use it, but it exists in my xml, so I either have to use it or ignore it. Either solution is fine.
Anyway, here is my starter code. It doesn't do anything but take an xpath query try to use it against the hard coded xml doc.
public static void main(String[] args) {
String query = args[0];
File XMLStream=null;
String xmlFileName="doc.xml";
OutputStream destStream=System.out;
XQueryExpression exp=null;
Configuration C=new Configuration();
C.setSchemaValidation(false);
C.setValidation(false);
StaticQueryContext SQC=new StaticQueryContext(C);
DynamicQueryContext DQC=new DynamicQueryContext(C);
QueryProcessor processor = new QueryProcessor(SQC);
Properties props=new Properties();
try{
exp=processor.compileQuery(query);
XMLStream=new File(xmlFileName);
InputSource XMLSource=new InputSource(XMLStream.toURI().toString());
SAXSource SAXs=new SAXSource(XMLSource);
DocumentInfo DI=SQC.buildDocument(SAXs);
DQC.setContextNode(DI);
SequenceIterator iter = exp.iterator(DQC);
while(true){
Item i = iter.next();
if(i != null){
System.out.println(i.getStringValue());
}
else break;
}
}
catch (Exception e){
System.err.println(e.getMessage());
}
}
An example XML file is here...
<?xml version="1.0"?>
<ns1:animal xmlns:ns1="http://my.catservice.org/">
<cat>
<catId>8889</catId>
<fedStatus>true</fedStatus>
</cat>
</ns1:animal>
If I run this with a query including the namespace, I get an error. For example:
/ns1:animal/cat/ gives the error: "Prefix ns1 has not been declared".
If I remove the ns1: from the query, it gives me nothing. If I doctor the xml to remove the "ns1:" prepended to "animal" I can run the query /animal/cat/ with success.
Any help would be greatly appreciated. Thanks.

Error message correctly points out that your xpath expression does not indicate what namespace prefix "ns1" means (binds to). Just because document to operate on happens to use binding for "ns1" does not mean it is what should be used: this because in XML, it's the namespace URI that matters, and prefixes are just convenient shortcuts to the real thing.
So: how do you define the binding? There are 2 generic ways; either provide a context that can resolve the prefix, or embed actual URI within XPath expression.
Regarding the first approach, this email from Saxon author mentions JAXP method XPath.setNamespaceContext(), similarly, Jaxen XPath processor FAQ has some sample code that could help
That's not very convenient, as you have to implement NamespaceContext, but once you have an implementation you'll be set.
So the notation approach... let's see: Top Ten Tips to Using XPath and XPointer shows this example:
to match element declared with namespace like:
xmlns:book="http://my.example.org/namespaces/book"
you use XPath name like:
{http://my.example.org/namespaces/book}section
which hopefully is understood by Saxon (or Jaxen).
Finally, I would recommend upgrading to Saxon9 if possible, if you have any trouble using one of above solutions.

If you want to have something working out of the box, you can check out embedding-xquery-in-java. There's github project, which uses Saxon to evaluate some sample XQuery expressions.
Regards