toObjects() with unknownTypeClass() and nested JSON is broken

[Kai-W]

Serializing a nestend Java object e.g. {"outer":{"inner":"value"}} results in an wrong java object. The values of the inner Object get additonally added to the outer object.

String json = "{\"outer\":{\"inner\":\"value\"}}";
System.out.println(json);
ReadOptions options = new ReadOptionsBuilder().unknownTypeClass(LinkedHashMap.class).build();
Object objects = JsonIo.toObjects(json,options, Object.class);
System.out.println(objects);
System.out.println(JsonIo.toJson(objects, null));

{"outer":{"inner":"value"}}
{inner=value, outer={inner=value}}
{"@type":"LinkedHashMap","inner":"value","outer":{"@type":"LinkedHashMap","inner":"value"}}

With no unknownType set or JsonObject as unkonwn type it works as expected but interestingly the resulting toJson is different. With explicit JsonObject as unknonwType there are no @type marks.

with unknownTypeClass(JsonObject.class)

JsonObject(id:-1, type:not set, target:null, line:0, col:0, size:1)
{"outer":{"inner":"value"}}

without any unknownTypeClass

JsonObject(id:-1, type:java.util.Map, target:null, line:0, col:0, size:1)
{"@type":"java.util.Map","outer":{"@type":"java.util.Map","inner":"value"}}

[Kai-W]

As mentioned in the commit message i tried to test with 4.60.0 if it was not reproducable / fixed.

On my Windows 11 maven install failes with 10 Failures

openjdk 21.0.8 2025-07-15 LTS
OpenJDK Runtime Environment Temurin-21.0.8+9 (build 21.0.8+9-LTS)
OpenJDK 64-Bit Server VM Temurin-21.0.8+9 (build 21.0.8+9-LTS, mixed mode, sharing)

[INFO] Results:
[INFO]
[ERROR] Failures:
[ERROR]   AutomaticFileTest.testBasicFileConversion:63
expected: "/home/user/document.txt"
 but was: "\home\user\document.txt"
[ERROR]   AutomaticFileTest.testConverterDirectly:50
expected: "/path/to/converted/file.txt"
 but was: "\path\to\converted\file.txt"
[ERROR]   AutomaticPathTest.testBasicPathConversion:64
expected: "/home/user/document.txt"
 but was: "\home\user\document.txt"
[ERROR]   AutomaticPathTest.testConverterDirectly:51
expected: "/path/to/converted/file.txt"
 but was: "\path\to\converted\file.txt"
[ERROR]   AutomaticPathTest.testRelativePath:106
expected: "./src/test/resources/data.json"
 but was: ".\src\test\resources\data.json"
[ERROR]   Issue425ExactReproTest.testExactIssueAsReported:48 Bug #425 reproduced: inner values are duplicated to outer level
[ERROR]   Issue425NestedJsonTest.testArrayWithNestedObjectsAndLinkedHashMap:209 First element should only have 'outer' ==> expected: <1> but was: <2>
[ERROR]   Issue425NestedJsonTest.testDeeplyNestedJsonWithLinkedHashMap:136 Top level should only have 'level1' ==> expected: <1> but was: <2>
[ERROR]   Issue425NestedJsonTest.testMultipleNestedPropertiesWithLinkedHashMap:174 Should have 3 keys at top level ==> expected: <3> but was: <5>
[ERROR]   Issue425NestedJsonTest.testNestedJsonWithLinkedHashMapDuplication:39 Top level should only have 'outer' key ==> expected: <1> but was: <2>
[INFO]
[ERROR] Tests run: 2138, Failures: 10, Errors: 0, Skipped: 12

The first errors are related to windows pahts using \ instead of /. Could be fixed to have the tests OS independent, e.g. using File.separator.
But the Tests regarding this Issue are failing
So I tried my WSL to check if it is OS depending

openjdk 21.0.8 2025-07-15
OpenJDK Runtime Environment (build 21.0.8+9-Ubuntu-0ubuntu124.04.1)
OpenJDK 64-Bit Server VM (build 21.0.8+9-Ubuntu-0ubuntu124.04.1, mixed mode, sharing)

[INFO] Results:
[INFO]
[ERROR] Failures:
[ERROR]   Issue425ExactReproTest.testExactIssueAsReported:48 Bug #425 reproduced: inner values are duplicated to outer level
[ERROR]   Issue425NestedJsonTest.testArrayWithNestedObjectsAndLinkedHashMap:209 First element should only have 'outer' ==> expected: <1> but was: <2>
[ERROR]   Issue425NestedJsonTest.testDeeplyNestedJsonWithLinkedHashMap:136 Top level should only have 'level1' ==> expected: <1> but was: <2>
[ERROR]   Issue425NestedJsonTest.testMultipleNestedPropertiesWithLinkedHashMap:174 Should have 3 keys at top level ==> expected: <3> but was: <5>
[ERROR]   Issue425NestedJsonTest.testNestedJsonWithLinkedHashMapDuplication:39 Top level should only have 'outer' key ==> expected: <1> but was: <2>
[ERROR] Errors:
[ERROR]   SecurityTest.testSecureWrites:47 » IO Cannot run program "ipconfig": error=2, No such file or directory
[INFO]
[ERROR] Tests run: 2138, Failures: 5, Errors: 1, Skipped: 12

Still the test for this issue are failing. And The SecurityTest cant find ipconfig. maybe change ipconfig to something that is always present when running the unittests e.g. java --version

[jdereg]

@Kai-W PR related to this issue has been merged and released in 4.61.0.

[Kai-W]

Now all Tests pass, thanks.