捕获异常后不终止反序列化过程

Question

Below is an example of my json :

[
    {
        firstKey : "value1",
        secondKey : "value2"
    },
    {
        firstKey : "value3",
        secondKey : "value4"
    }
]

I am deserializing the api response (json) to java object using Jackson Object Mapper.

However, while deserializing, when the JSON object returned has extra key (not present in POJO), the whole program terminates. I want the code to deserialize all the JSON Objects inside the JSONARRAY and then throw all the exceptions at the end.

Answer 1

One way to achieve this would be to create a custom deserializer that loops the Json array/list and inspects each item individually at the same time collecting possible errors.

First we would need models to describe Json structure. First the actual item:

@Getter @Setter
public class KeyHolder {
    private String firstKey;
    private String secondKey;
}

Then a simple helper class to represent the list adn make the code a bit cleaner:

@SuppressWarnings("serial")
@JsonDeserialize(using = KeyHolderListDeserializer.class )
public class KeyHolderList extends ArrayList<KeyHolder> {}

Note the annotation @JsonDeserialize m it will then trigger the custom deserializer shown below:

public class KeyHolderListDeserializer extends JsonDeserializer<KeyHolderList> {
    // This is just an example exception how you could wrap the exceptions to one
    @SuppressWarnings("serial")
    @RequiredArgsConstructor
    public static class ValidationException extends RuntimeException {
        @Getter
        private final Map<Integer, Exception> failedObjects;
    }

    @Override
    public KeyHolderList deserialize(JsonParser p, DeserializationContext ctxt) 
            throws IOException, JsonProcessingException {
        KeyHolderList readObjects = new KeyHolderList();
        Map<Integer, Exception> failedObjects = new HashMap<>();
        ObjectMapper om = new ObjectMapper();
        int i = 0;
        // Read values first as tree ignoring type and validness
        TreeNode listNode = p.readValueAsTree();
        for (; i < listNode.size(); i++) {
            TreeNode itemNode = listNode.get(i);
            try {
                // Then in this loop try to instantiate each one indivually
                // storing the succeeded ones...
                readObjects.add(om.treeToValue(itemNode, KeyHolder.class));
            } catch (Exception e) {
                // ... and reporting the failing ones
                failedObjects.put(i, e);
            }
        }
        // Finally you can do liek below or whatever you need to do with the results
        if(failedObjects.isEmpty()) {
            return readObjects;            
        }
        throw new ValidationException(failedObjects);
    }

}

After these it is just:

KeyHolderList keyHolderList = om.readValue(YOUR_JSON_SOURCE, KeyHolderList.class);