Support for generic types when serializing and deserializing?

[Bartłomiej Mazur]

Currently SnakeYaml only support beans deserialization via:

public <T> T loadAs(String yaml, Class<T> type)

This make near impossible to write some own library for some serialization/deserialization using snakeyaml, especially if data isn't made by us and does not contain type tags in it.

It would be awesome to be able to use methods like this:

public <T> T loadAs(String yaml, Type type)
public String dumpAs(Object object, Type type) // will not include type tags for known types that can be read from generic

Just like in GSON library.

As I see you often want to see some test cases describing issue, I attached one, but ofc code will not compile, as this is request for new methods that will support that features. Test requires GSON, as I didn't want to include whole TypeToken<T> API.

[Andrey Somov]

If you deliver the pull request with the implementation this month, we can include it in the coming release in August.

[Bartłomiej Mazur]

Sorry, I do not have time in this month. Any chance that you will do it later? If not, then maybe I will find some time in next months, but just not in this one.

[Alexander Maslov]

Issue #388 was marked as a duplicate of this issue.

[Anthony Foulfoin]

Same issue for me. My yaml document root is a list of TestCase:

- input: ["val1","val2"]
  expected: ["val3","val4"]
- input: ["val5","val6"]
  expected: ["val7","val8"]

TestCase:

public class TestCase {
        public List<String> input;
        public List<String> expected;
 }

I try to use SnakeYaml to deserialize it as a List<TestCase>:

List<TestCase> tests = new Yaml().load(is);

Unfortunately I get a List of HashMap instead, I didn't find any way in SnakeYaml to provide the List generic type.

With jackson, when deserializing json, we can use a TypeRefence to do this, example with jackson and the same document in json:

List<TestCase> tests = mapper.readValue(is, new TypeReference<List<TestCase>>(){});

What I get is effectively a List<TestCase>!

I found out a little hack to achieve this with SnakeYaml, I try to deserialize to a typed array first, then convert the array into a List. Since arrays are statically typed it works !

TestCase[] testsArray = new Yaml().loadAs(is, TestCase[].class);
List<TestCase> tests = Arrays.asList(testArray);

I get a List<TestCase> like I wanted, but it looks very hacky and it would be great if SnakeYaml could natively support a mecanism like Jackson (or Gson)

Thanks !

[Alan Wang]

@Anthony Foulfoin this issue may be fixed by PR #5

[Ling Hengqian]

The problem I found was related to this problem, but I encountered a very strange situation. The YAML I tested here can be deserialized normally in snakeyaml 1.16 version , but the generic information is lost in snakeyaml 1.19-1.30 version .

Take the following program as an example, it works fine on snakeyaml 1.16-1.18, but in1.19-1.30 version the generic information is lost, causing ClassCastException.

public enum ExecuteProcessConstants {
    EXECUTE_ID, EXECUTE_STATUS_START, EXECUTE_STATUS_DONE
}

@NoArgsConstructor
@AllArgsConstructor
@Data
public class YamlExecuteProcessUnit {
    private String unitID;
    private ExecuteProcessConstants status;
}

@NoArgsConstructor
@AllArgsConstructor
@Data
public class YamlExecuteProcessContext {
    private String executionID;
    private String schemaName;
    private String username;
    private String hostname;
    private String sql;
    private Collection<YamlExecuteProcessUnit> unitStatuses;
    private Long startTimeMillis;
}

public class JunitTest {
  @Test
  public void snakeYamlTest3() {
    String marshal = "unitStatuses: !!set\n" +
            "  ? status: EXECUTE_STATUS_DONE\n" +
            "    unitID: '159917166'\n" +
            "  : null\n";
    YamlExecuteProcessContext unmarshal = new Yaml(new Constructor(YamlExecuteProcessContext.class)).loadAs(marshal,YamlExecuteProcessContext.class);
    for (YamlExecuteProcessUnit unit : unmarshal.getUnitStatuses()) {
        System.out.println("test problem in class ---------" + unit.getClass().getName());
        if (unit.getStatus() != ExecuteProcessConstants.EXECUTE_STATUS_DONE) {
            return;
        }
    }
  }
}

The discovery of this issue is related to https://github.com/apache/shardingsphere/pull/15260 , and a separate test case is linked to snakeyaml-update-test/JunitTest.java at master · linghengqian/snakeyaml-update-test (github.com) .
Hope some friends can tell me the reason, I didn't see enough information in the update log of snakeyaml 1.19 to support the problem.

‌

[Alexander Maslov]

this is a nice one 6 years nobody reported it. I have a fix for this.

Not sure it is related to this issue, but let’s see. I need to write maybe couple of tests to see what kind of situation it fixes.
At least no current tests are failing. And your test is also passing.

[Alexander Maslov]

change how we set detected type to JavaBean Collection property item

fixes regression introduced in 1.19 when generics information is lost for JavaBean Collection property.

refs issue #387

→ <<cset 9d7dbb869ba9>>

[Alexander Maslov]

change how we set detected type to JavaBean Collection property item

fixes regression introduced in 1.19 when generics information is lost for JavaBean Collection property.

refs issue #387

→ <<cset 6385279ecb0b>>

[Ling Hengqian]

• thank you very much! I think this issue can be closed.

‌