getOutputStream() has already been called spring boot

Question

I'm trying to do a query in a many to many relationship. The result is a large Json that makes no sense for me and an error in the spring console.

I don't know why this is happening. I was guided by tutorials to do the many to many relationship.

This is the repository

public interface ProductJpaRepository extends JpaRepository<Customer, Long> {
    @Query(value = "select p from Product p where p.productoId = ?1")
    Product findByProductId(Long productId);    

    List<Customer> findBycustomerId(Long customerId); 
}

This is the product

...

@Id
@GeneratedValue(strategy=GenerationType.AUTO)
@Column(name="PRODUCTO_ID")
private long productoId;
private String name;
private Long price;
@ManyToMany(mappedBy = "products")
private Set<Customer> customers = new HashSet<>();

...

This the Customer

...

@Id
@GeneratedValue
private Long customerId;
private String name;
private String email;

@ManyToMany(cascade = {CascadeType.ALL})
@JoinTable(
    name= "PRODUCTS_BY_CUSTOMER",
    joinColumns = { @JoinColumn(name = "CUSTOMER_CUSTOMER_ID")},
    inverseJoinColumns = { @JoinColumn(name = "PRODUCT_PRODUCTO_ID")}
) 
Set<Product> products = new HashSet<>();

...

This is the controller

...

@GetMapping(value = "productsList/{productId}")
public Product findByProductId(@PathVariable final Long productId){
    return productJpaRepository.findByProductId(productId); 
}

...

and this is the result when I put in the browser http://localhost:8180/products/productsList/3. This result extends much more, I only attach a part but the rest is the same

{
  "productoId":3,
  "name":"Producto C",
  "price":4000,
  "customers": [
    {
      "customerId":1,
      "name":"Carlos Rodriguez",
      "email":"[email protected]",
      "products":[
        {
          "productoId":3,
          "name":"Producto C",
          "price":4000,
          "customers":[
            {
              "customerId":1,
              "name":"Carlos Rodriguez",
              "email":"[email protected]",
              "products":[
                {
                  "productoId":3,
                  "name":"Producto C",
                  "price":4000,
                  "customers":[
                    {
                    "customerId":1,
                    "name":"Carlos Rodriguez",
                    "email":"[email protected]"
                    ....

And finally this is the error in the console

2017-10-29 20:17:05.458 ERROR 1640 --- [nio-8180-exec-1] o.a.c.c.C.[Tomcat].[localhost]           : Exception Processing ErrorPage[errorCode=0, location=/error]

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is java.lang.IllegalStateException: getOutputStream() has already been called for this response
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:982) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:635) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:742) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:101) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:101) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:101) ~[spring-web-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:728) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.ApplicationDispatcher.doInclude(ApplicationDispatcher.java:590) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.ApplicationDispatcher.include(ApplicationDispatcher.java:524) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.StandardHostValve.custom(StandardHostValve.java:389) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.StandardHostValve.status(StandardHostValve.java:254) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.StandardHostValve.throwable(StandardHostValve.java:349) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:175) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_131]
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_131]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-8.5.23.jar:8.5.23]
    at java.lang.Thread.run(Thread.java:748) [na:1.8.0_131]
Caused by: java.lang.IllegalStateException: getOutputStream() has already been called for this response
    at org.apache.catalina.connector.Response.getWriter(Response.java:625) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.apache.catalina.connector.ResponseFacade.getWriter(ResponseFacade.java:211) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at javax.servlet.ServletResponseWrapper.getWriter(ServletResponseWrapper.java:109) ~[tomcat-embed-core-8.5.23.jar:8.5.23]
    at org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration$SpelView.render(ErrorMvcAutoConfiguration.java:227) ~[spring-boot-autoconfigure-1.5.8.RELEASE.jar:1.5.8.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1286) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1041) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:984) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970) ~[spring-webmvc-4.3.12.RELEASE.jar:4.3.12.RELEASE]

Answer 1

You have a composition of Customer in your Product entity and vice versa.

You are getting this error because of the un-ending serialization that is going while converting your entity Product to JSON.

Try either

• JsonIgnore on customers in the Product entity.

• Instead of serializing the complete Product object, create a DTO class ProductDto that contains only the fields you want at the client side.

  @GetMapping(value = "productsList/{productId}")
  public ProductDto findByProductId(@PathVariable final Long productId){
      Product product = productJpaRepository.findByProductId(productId); 
      ... 
      //get required properties from product and set in the ProductDto object
      return productDto;
  }