getOutputStream() has already been called for this response when fill data in child table with spring boot - spring

Question

I am using spring boot 1.5.10 & spring rest to develop some rest services
I have relation one to many between product and services.
When I fill data in services table and access the service that get me all products(http://localhost:8080/user/products) give me this exception:
Caused by: java.lang.IllegalStateException: getOutputStream() has
already been called for this response.
and repeated json appear in the browser!
If services table is empty: no exception is thrown. I don't know why.
I found a link that discuss the problem but yet I couldn't solve it.
Product entity:
#Entity
#Table(name = "products")
public class Product implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Basic(optional = false)
#Column(name = "ID")
private Integer id;
#Basic(optional = false)
#Column(name = "NAME")
private String name;
#OneToMany(cascade = CascadeType.ALL, mappedBy = "productId")
private List<Service> servicesList;
}
Service Entity:
#Entity
#Table(name = "services")
public class Service implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Basic(optional = false)
#Column(name = "ID")
private Integer id;
#Basic(optional = false)
#Column(name = "NAME")
private String name;
#Basic(optional = false)
#Column(name = "TYPE")
private int type;
#JoinColumn(name = "PRODUCT_ID", referencedColumnName = "ID")
#ManyToOne(optional = false)
private Product productId;
}
And the ProductController
#Controller
#RequestMapping("user")
#CrossOrigin(origins="http://localhost:4200", allowedHeaders="*")
public class ProductController {
#Autowired
private IProductService productService;
#GetMapping("product/{id}")
public ResponseEntity<Product> getProductById(#PathVariable("id") Integer id) {
Product product = productService.getProductById(id);
return new ResponseEntity<Product>(product, HttpStatus.OK);
}
#GetMapping("products")
public ResponseEntity<List<Product>> getAllProducts() {
List<Product> list = productService.getAllProducts();
return new ResponseEntity<List<Product>>(list, HttpStatus.OK);
}
}
pom.xml is defined as follows.
http://maven.apache.org/xsd/maven-4.0.0.xsd">
4.0.0
<groupId>com.app</groupId>
<artifactId>Assignment</artifactId>
<version>0.0.1-SNAPSHOT</version>
<packaging>jar</packaging>
<name>Assignment</name>
<description>Demo project for Spring Boot</description>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>1.5.10.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>

Answer 1

As discussed in the link you have shared, you need to create a response class to be sent to the client who is calling the API.
For example, you might have a class saying ProductResponse which might look like this.
public class ProductResponse implements Serializable {
public Integer id;
public String name;
public List<Service> servicesList;
}
Now in the controller class, populate create the response as follows.
#GetMapping("product/{id}")
public ResponseEntity<ProductResponse> getProductById(#PathVariable("id") Integer id) {
Product product = productService.getProductById(id);
ProductResponse productResponse = createProductResponse(product);
return new ResponseEntity<ProductResponse>(productResponse, HttpStatus.OK);
}
ProductResponse createProductResponse(Product product) {
ProductResponse productResponse = new ProductResponse();
productResponse.id = product.id;
productResponse.name = product.name;
productResponse.serviceList = product.serviceList;
}
And yes, you need to specify the FetchType.EAGER in the entity class of Product.
#Entity
#Table(name = "products")
public class Product implements Serializable {
// ... Other parameters
#OneToMany(fetch = "FetchType.EAGER", cascade = CascadeType.ALL, mappedBy = "productId")
private List<Service> servicesList;
}
Hope that helps.