Wim Deblauwe
❯ blog / 2018 / 06 / 10

PageImpl JSON serialization with Spring Boot 2

June 10, 2018 · 2 min read spring-boot

During the migration of a Spring Boot application from 1.5.13 to 2.0.2, some of my Spring Rest Docs tests started failing. The reason being that some of my RestController s return a org.springframework.data.domain.PageImpl object (from Spring Data Commons).

@RestController
public class MyRestController {

    @GetMapping
    public PageImpl<SomeDtoObject> listAll() {
        ...
    }
}

With Spring Boot 1.5.13, this results in JSON like this:

{
  "content": [
    {
      ...
    },
    {
      ...
    },
    ....
  ],
  "totalElements": 50,
  "totalPages": 3,
  "last": false,
  "size": 20,
  "number": 0,
  "numberOfElements": 1,
  "first": true,
  "sort": [
    {
      "direction": "DESC",
      "property": "date",
      "ignoreCase": false,
      "nullHandling": "NATIVE",
      "ascending": false,
      "descending": true
    }
  ]
}

However, with Spring Boot 2.0.2 (which includes Spring Data Commons 2.0.7), the resulting JSON is quite different:

{
  "content": [
    {
      ...
    },
    {
      ...
    },
    ....
  ],
  "pageable": {
    "sort": {
      "sorted": true,
      "unsorted": false
    },
    "offset": 0,
    "pageNumber": 0,
    "pageSize": 20,
    "paged": true,
    "unpaged": false
  },
  "totalPages": 3,
  "last": false,
  "totalElements": 50,
  "size": 20,
  "number": 0,
  "numberOfElements": 1,
  "sort": {
    "sorted": true,
    "unsorted": false
  },
  "first": true
}

The content element is still there, but the others are quite different.

In order to have the same back as before, add a custom JSON serializer:

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import org.springframework.boot.jackson.JsonComponent;
import org.springframework.data.domain.PageImpl;
import org.springframework.data.domain.Sort;
import java.io.IOException;

@JsonComponent
public class PageImplJacksonSerializer extends JsonSerializer<PageImpl<?>> {

    @Override
    public void serialize(PageImpl page, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {

        jsonGenerator.writeStartObject();
        jsonGenerator.writeObjectField("content", page.getContent());
        jsonGenerator.writeBooleanField("first", page.isFirst());
        jsonGenerator.writeBooleanField("last", page.isLast());
        jsonGenerator.writeNumberField("totalPages", page.getTotalPages());
        jsonGenerator.writeNumberField("totalElements", page.getTotalElements());
        jsonGenerator.writeNumberField("numberOfElements", page.getNumberOfElements());

        jsonGenerator.writeNumberField("size", page.getSize());
        jsonGenerator.writeNumberField("number", page.getNumber());

        Sort sort = page.getSort();

        jsonGenerator.writeArrayFieldStart("sort");

        for (Sort.Order order : sort) {
            jsonGenerator.writeStartObject();
            jsonGenerator.writeStringField("property", order.getProperty());
            jsonGenerator.writeStringField("direction", order.getDirection().name());
            jsonGenerator.writeBooleanField("ignoreCase", order.isIgnoreCase());
            jsonGenerator.writeStringField("nullHandling", order.getNullHandling().name());
            jsonGenerator.writeEndObject();
        }

        jsonGenerator.writeEndArray();
        jsonGenerator.writeEndObject();
    }
}

Spring Boot will automatically pick this up (Due to the @JsonComponent annotation) to serialize the PageImpl objects.