Spring boot REST API Returning a List/Array Formatting issue

Question

I am developing spring boot based web services API. I need to return a list of things (ProductData) for the GET response.

This is what the response looks like

<ProductDataList>
  <ProductData>
     <ProductData>...</ProductData>
     <ProductData>...</ProductData>
     <ProductData>...</ProductData>
  </ProductData>
</ProductDataList>

But I don't need the extra <ProductData> tag. I need the response as below.

  <ProductDataList>
    <ProductData>...</ProductData>
    <ProductData>...</ProductData>
    <ProductData>...</ProductData>
  </ProductDataList>

Any idea why an extra tag is generated?

I have below in my WebMvcConfig file.

  @Bean
public MappingJackson2XmlHttpMessageConverter xmlConverter() {
    Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder();
    builder.propertyNamingStrategy(PropertyNamingStrategy.
            PascalCaseStrategy.PASCAL_CASE_TO_CAMEL_CASE);
    builder.serializationInclusion(JsonInclude.Include.NON_EMPTY);
    builder.failOnUnknownProperties(false);
    MappingJackson2XmlHttpMessageConverter xmlConverter =
            new MappingJackson2XmlHttpMessageConverter(builder.createXmlMapper(true).build());
    return xmlConverter;
}

In my controller I have

@RequestMapping(value = "/productdata")
@ResponseBody
public ProductDataList getProductData(@RequestParam final String[] ids) {        
    ArrayList<ProductData> products = productDataService.getProductData(ids);

    ProductData[] pdArray = new ProductData[products.size()];
    products.toArray(pdArray);
    ProductDataList productDataList = new ProductDataList();
    productDataList.setProductData(pdArray);

    return productDataList;
}

This is my ProductDataList class.

public class ProductDataList{

     ProductData[] productData;

     public ProductData[] getProductData() {
           return productData;
     }

     public void setProductData(ProductData[] productData) {
           this.productData = productData;
     }
}

Edit 1.

When I return ArrayList<ProductData> the response was like this.

<ArrayList>
  <item>...</item>
  <item>...</item>
  <item>...</item>
</ArrayList>

Edit 2. After adding annotation JsonTypeInfo I made some progress, but not quite there to what I wanted.

@JsonTypeInfo(use = JsonTypeInfo.Id.NAME, include = JsonTypeInfo.As.PROPERTY)
public class ProductData {}

<ProductDataList>
     <item _type="ProductData">...</item>
     <item _type="ProductData">...</item>
     <item _type="ProductData">...</item>
<ProductDataList>

Why you did not just return the ArrayList<ProductData> products? — Ali Dehghani
– Ali Dehghani, Commented Apr 12, 2016 at 18:14

Kieron Alsmith · Accepted Answer · 2016-04-12 19:12:29Z

1

Objects aren't built that way. It's doing exactly as you're asking:

<ProductDataList>   <!-- the ProductDataList object -->
  <ProductData>     <!-- the property containing the array -->
    <ProductData>...</ProductData>  <!-- each ProductData object -->
    <ProductData>...</ProductData>
    <ProductData>...</ProductData>
  </ProductData>
</ProductDataList>

This is to ensure that other properties on the ProductDataList object would also have a spot inside the tags, e.g.

<ProductDataList>
  <MyArray>...</MyArray>
  <MyProperty></MyProperty>
</ProductDataList>

To get around this, you might as well try to cut out the Object middle-man.

@RequestMapping(value = "/productdata")
@ResponseBody
public ArrayList<ProductData> getProductDataList(@RequestParam final String[] ids) {
    return productDataService.getProductData(ids);
}

If it works at all (I seem to remember JAXB not being able to parse ArrayLists), your ObjectMapper will give you...

<ArrayList>
  <ProductData>...</ProductData>
  <ProductData>...</ProductData>
  <ProductData>...</ProductData>
</ArrayList>

...instead of the root tag that you're hoping for. But if it DOES work, then just create a class that extends ArrayList and doesn't do anything, then return it instead.

public class ProductDataList<E> extends ArrayList<E>{ ... }

And then...

@RequestMapping(value = "/productdata")
@ResponseBody
public ProductDataList<ProductData> getProductDataList(@RequestParam final String[] ids) {
    return (ProductDataList) productDataService.getProductData(ids);
}

Happy hunting.

Kieron

answered Apr 12, 2016 at 19:12

Kieron Alsmith

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2 Comments

ravindrab Over a year ago

When ArrayList<ProductData> is returned what I see is a list of <item>...</item> instead of <ProductData>...</ProductData> elements. See the edit.

Kieron Alsmith Over a year ago

Maybe try making "public class ProductDataList<ProductData> extends ArrayList<E> { /* blah */ }" -- maybe the typed <E> object cast in the class will make the XML ObjectMapper grab the classname instead of "item". If not, it seems like you may need to add some sort of custom ObjectMapper for this new ProductDataList object.

Community · Accepted Answer · 2017-05-23 10:28:34Z

After some effort I was able to get this resolved. Key thing is to have @JacksonXmlElementWrapper(useWrapping = false) in the Object as mentioned in this answer

@JacksonXmlRootElement(localName = "ProductDataList")
public class ProductDataList {

    @JacksonXmlProperty(localName = "ProductData")
    @JacksonXmlElementWrapper(useWrapping = false)
    ProductData[] productDataArray = null;

    public ProductData[] getProductDataArray() {
        return productDataArray;
    }

    public void setProductDataArray(ProductData[] productDataArray) {
        this.productDataArray = productDataArray;
    }
}

Now the response looks like just as I wanted to be.

<ProductDataList>
    <ProductData>...</ProductData>
    <ProductData>...</ProductData>
    <ProductData>...</ProductData>
</ProductDataList>

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