我尝试用java -hib- spring实现一个服务器REST，它返回一个json。
我已经Map了多对多关系。
我解释得更好，我有一个供应商，有一个成分列表，每个成分都有一个供应商列表。
我创建了表：

CREATE TABLE supplier_ingredient (
  supplier_id BIGINT,
  ingredient_id BIGINT
)

ALTER TABLE supplier_ingredient ADD CONSTRAINT supplier_ingredient_pkey 
PRIMARY KEY(supplier_id, ingredient_id);

ALTER TABLE supplier_ingredient ADD CONSTRAINT 
fk_supplier_ingredient_ingredient_id FOREIGN KEY (ingredient_id) 
REFERENCES ingredient(id);

ALTER TABLE supplier_ingredient ADD CONSTRAINT 
fk_supplier_ingredient_supplier_id FOREIGN KEY (supplier_id) REFERENCES 
supplier(id);

然后我有了成分型号：

.....
.....
@ManyToMany(mappedBy = "ingredients")
@OrderBy("created DESC")
@BatchSize(size = 1000)
private List<Supplier> suppliers = new ArrayList<>();
....
....

然后我有供应商型号：

....
@ManyToMany
@JoinTable( name = "supplier_ingredient ", 
        joinColumns = @JoinColumn(name = "supplier_id", referencedColumnName = "id"), 
        inverseJoinColumns = @JoinColumn(name = "ingredient_id", referencedColumnName = "id"), 
        foreignKey = @ForeignKey(name = "fk_supplier_ingredient_supplier_id"))
@OrderBy("created DESC")
@Cascade(CascadeType.SAVE_UPDATE)
@BatchSize(size = 1000)
private List<Ingredient> ingredients = new ArrayList<>();
....

终点：

@RequestMapping(value = "/{supplierId:[0-9]+}", method = RequestMethod.GET)
@ResponseStatus(value = HttpStatus.OK)
@ResponseBody
public SupplierObject get(@PathVariable Long supplierId) {

    Supplier supplier = supplierService.get(supplierId);

    SupplierObject supplierObject = new SupplierObject (supplier);

    return SupplierObject;

}

服务

....
public Supplier get(Long supplierId) {

    Supplier supplier = supplierDao.getById(supplierId); (it does entityManager.find(entityClass, id))

    if (supplier == null) throw new ResourceNotFound("supplier", supplierId);

    return supplier;
}
....

供应商对象

@JsonIgnoreProperties(ignoreUnknown = true)
    public class SupplierObject extends IdAbstractObject {

    public String email;

    public String phoneNumber;

    public String address;

    public String responsible;

    public String companyName;

    public String vat;

    public List<Ingredient> ingredients = new ArrayList<>();

    public SupplierObject () {

    }

    public SupplierObject (Supplier supplier) {

        id = supplier.getId();
        email = supplier.getEmail();
        responsible = supplier.getResponsible();
        companyName = supplier.getCompanyName();
        phoneNumber = supplier.getPhone_number();
        ingredients = supplier.getIngredients();
        vat = supplier.getVat();
        address = supplier.getAddress();

    }
}

和标识抽象对象

public abstract class IdAbstractObject{

    public Long id;

}

我的问题是，当我调用端点时：

http://localhost:8080/supplier/1

出现错误：
“无法写入JSON：无法延迟初始化角色集合：无法初始化代理-无会话;嵌套的异常是com.fasterxml.Jackson.databind.jsonMappingException：无法延迟初始化角色集合：myPackage.ingredient.Ingredient.suppliers，无法初始化代理-无会话（通过引用链：我的软件包.供应商.供应商对象[\“成分"]-〉组织.休眠.集合.内部.持久性包[0]-〉我的软件包.成分.成分[\“供应商"]）”
我接着说：
避免对未提取的惰性对象进行Jackson序列化
现在我还没有这个错误但是在json返回的时候，配料字段是null：

{
  "id": 1,
  "email": "mail@gmail.com",
  "phoneNumber": null,
  "address": null,
  "responsible": null,
  "companyName": "Company name",
  "vat": "vat number",
  "ingredients": null
}

但是在调试中我可以看到一些成分....