Clarify behavior for generics support in BeanUtils.copyProperties

[afattahi54]

The below code works in 5.2.9.RELEASE

BeanUtils.copyProperties(transferVO , transferRequest);

The classes where as follow. As you can see the source and destination beans has a List with same name but different types. But it was working

public class transferVO {
	private List<Signer> signers;
}

public class transferRequest{	
	private List<TransferSigners > signers;

}


public class Signer{
    private string name;

}

public class TransferSigners {    
    private string name;
}

After upgrade to 5.3.7 the signers property is not copied.

[sbrannen]

This is a potential regression introduced in conjunction with #24187.

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@afattahi54, can you please also provide the setter and getter methods of those two classes so that we can inspect the actual method signatures?

Also, if Signer is not a subtype of TransferSigners, why would you expect BeanUtils to copy from List<Signer> to List<TransferSigners>?

Doing so would actually store items in the List<TransferSigners> that are not an instance of TransferSigners, and that would be a broken state.

[afattahi54]

The Signer and TransferSigners do not have same types. You are right, but as it was working before upgrade to 5.3.7 I expected it to keep working

The setters and getters are as below:

public class transferVO {
        private List<Signer> signers;
	public List<Signer> getSigners() {
		return signers;
	}

	public void setSigners(List<Signer> signers) {
		this.signers = signers;
	}

}

public class transferRequest {

       private List<TransferSigners > signers;
	public List<TransferSigners> getSigners() {
		return signers;
	}
	public void setSigners(List<TransferSigners> signers) {
		this.signers = signers;
	}

}

Thanks

[bigdata-page]

This is a potential regression introduced in conjunction with #24187.

@afattahi54, can you please also provide the setter and getter methods of those two classes so that we can inspect the actual method signatures?

Also, if Signer is not a subtype of TransferSigners, why would you expect BeanUtils to copy from List<Signer> to List<TransferSigners>?

Doing so would actually store items in the List<TransferSigners> that are not an instance of TransferSigners, and that would be a broken state.

@sbrannen spring-beans version is 5.3.9, when Signer is a subtype of TransferSigners，use the BeanUtils.copyProperties(transferVO , transferRequest). the transferVO.signers is null. but when spring-beans version is 5.1.16.RELEASE is normal. I hope the new version is compatible with the previous version.

[sbrannen]

Assigned to the Triage Queue so that the team can determine if this is a regression that needs to be fixed.

[sbrannen]

The Signer and TransferSigners do not have same types. You are right, but as it was working before upgrade to 5.3.7 I expected it to keep working

@afattahi54, since BeanUtils.copyProperties() honors generics since Spring Framework 5.3, you will need to ensure that the source and target property types are compatible in terms of Java semantics.

spring-beans version is 5.3.9, when Signer is a subtype of TransferSigners，use the BeanUtils.copyProperties(transferVO , transferRequest). the transferVO.signers is null. but when spring-beans version is 5.1.16.RELEASE is normal. I hope the new version is compatible with the previous version.

@bigdata-page, that can be addressed by using an upper-bounded wildcard for the target property type.

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In commit 887389d, I added a table to the Javadoc for BeanUtils.copyProperties() which will hopefully help you and other users better understand the current semantics for property type matching.