Using Jackson2 with Spring 4.0 (MVC + REST + Hibernate)

Question

I am making a sedative application and trying to convert a list of objects to json for a specific URL (@ RequestMapping / @ ResponseBody)

I have jackson-hibernate4 and jackson-core, databind etc in my class path.

Here is my object that I want to convert to json.

@Entity
@Table(name="Product")
public class Product {
@Id
@Column(name="productId")
@GeneratedValue
protected int productId;
@Column(name="Product_Name")
protected String name;

@Column(name="price")
protected BigDecimal baseprice;


@OneToMany(cascade = javax.persistence.CascadeType.ALL,mappedBy="product",fetch=FetchType.EAGER)
protected List<ProductOption> productoption = new ArrayList<ProductOption>();

@OneToMany(cascade = javax.persistence.CascadeType.ALL,mappedBy="product",fetch=FetchType.EAGER)
protected List<ProductSubOption> productSubOption = new ArrayList<ProductSubOption>();


@ManyToOne
@JoinColumn(name="ofVendor")
protected Vendor vendor;

Two objects inside Product are also POJO'S.

Here is my method that retrieves a list of products

@Override
public List<Product> getMenuForVendor(int vendorId) {
    List<Product> result = em.createQuery("from "+Product.class.getName()+" where ofVendor = :vendorId").setParameter("vendorId", vendorId).getResultList();
    System.out.println(result.size());
    return result;
}

When I try to return this list to my controller, I get the message "Can not lazily load for json", so I want my objects to be loaded impatiently. Here is my controller

@Autowired
private MenuDaoImpl ms;

@RequestMapping(value = "/{vendorId}", method = RequestMethod.GET)
public @ResponseBody List<Product> getMenu(@PathVariable int vendorId){

    List<Product> Menu = Collections.unmodifiableList(ms.getMenuForVendor(vendorId));
    return Menu;
}

Now that I find my localhost url: 8080 / getMenu / 1, I should get the json string, but I get a large list of errors.

WARN : org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver -       Handling of [org.springframework.http.converter.HttpMessageNotWritableException] resulted in Exception
  java.lang.IllegalStateException: Cannot call sendError() after the response has been     committed
at org.apache.catalina.connector.ResponseFacade.sendError(ResponseFacade.java:467)
 Could not write JSON: Infinite recursion (StackOverflowError) (through reference chain:

I'm not sure something is missing. Please guide.

Answer 1

@JsonBackReference @ManyToOne @JsonManagedReference @OneToMany.

"Sotirios Delimanolis"

Answer 2

. , , . http://geekabyte.blogspot.in/2013/09/fixing-converterhttpmessagenotwritablee.html

Answer 3

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, Json Json. Jackson, ( - 2 , , ).

HttpMessageConverter:

   @Bean
    public HttpMessageConverter jacksonMessageConverter() {
        MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
        converter.setPrefixJson(false);
        converter.setPrettyPrint(true);
        converter.setObjectMapper(objectMapper());
        return converter;
    }

ObjectMapper, , .

public ObjectMapper objectMapper() {
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.configure(SerializationFeature.INDENT_OUTPUT, true);

    SimpleModule module = new SimpleModule("jacksonJsonMapper", Version.unknownVersion());
    module.addSerializer(Product.class, new Product());

    objectMapper.registerModule(module);

    return objectMapper;
}

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public class Product erializer extends JsonSerializer<Product> {

@Override
public void serialize(Product product, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
    if(product == null) { 
        //Handle it, if you want 
    }

    if(product != null) {

        jsonGenerator.writeStartObject();

        jsonGenerator.writeStringField("id", productId.getId().toString());
        jsonGenerator.writeStringField("title",  product.getName());
        jsonGenerator.writeStringField("basePrice", product.getBasePrice());


        //Add items to the json array representation
        jsonGenerator.writeArrayFieldStart("productoptions");
        for(ProductOption productOption: product.getProductoption()) {
            jsonGenerator.writeStartObject("field", productOption.getFoo());

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

        jsonGenerator.writeEndObject();
    }
}

}

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