如何在 WebService (java) 上返回 List<T>

Posted 2023-02-19

【中文标题】如何在 WebService (java) 上返回 List<T>

【英文标题】：How return List<T> on WebService (java)

【发布时间】：2017-11-01 01:17:08

【问题描述】：

我需要在 WebService 上返回不同的列表，目前我在一个封装文件中有超过 15 种不同的类型，但很难操作许多构造函数：

public class ResponseMessage implements java.io.Serializable 

    private Integer code;
    private String message;
    private List<Users> listUsers;
    private List<Products> listProducts;
    private List<Customers> listCustomers;
    private List<Suppliers> listSuppliers;
    private List<Reports> listReports;
    ...
    private Users userById;
    private Products productById;
    private Customers customerById;
    private Suppliers supplierById;
    ...

    public ResponseMessage() 
    

    //My idea is something like that, not work
    public ResponseMessage(Integer code, String message, List<T> lstData) 
        this.code = code;
        this.message = message;
        this.lstData = lstData;
    

    public ResponseMessage(Integer code, String message, T uniqueData) 
        this.code = code;
        this.message = message;
        this.uniqueData = uniqueData;
    

    //Currently the constructor are this, work
    public ResponseMessage(Integer code, String message, List<Users> listUsers) 
        this.code = code;
        this.message = message;
        this.listUsers = listUsers;
    

    public ResponseMessage(Integer code, String message, List<Users> listUsers, List<Customers> listCustomers) 
        this.code = code;
        this.message = message;
        this.listUsers = listUsers;
        this.listCustomers = listCustomers;
    

    public ResponseMessage(Integer code, String message, List<Users> listUsers, List<Customers> listCustomers, List<Suppliers> listSuppliers) 
        this.code = code;
        this.message = message;
        this.listUsers = listUsers;
        this.listCustomers = listCustomers;
        this.listSuppliers = listSuppliers;
    

    ...

    //Same history with unique result, work
    public ResponseMessage(Integer code, String message, Users userById) 
        this.code = code;
        this.message = message;
        this.userById = userById;
    

    public ResponseMessage(Integer code, String message, Users userById, Products productById) 
        this.code = code;
        this.message = message;
        this.userById = userById;
        this.productById = productById;
    

    //Getters and Setters

当我喜欢在 WebService 上返回构造函数时，我必须这样做，例如（工作）：

public ResponseMessage readAllSuppliers() 
   List<Suppliers> lstsuppliers = new ArrayList<Suppliers>();
   lstsuppliers = supplierDAO.getAllSuppliers();
   //ResponseMessage(code, message, user, customer, supplier list or unique supplier)
   ResponseMessage rm = new ResponseMessage(123, "reading suppliers", null, null, lstsuppliers);
   return rm;

但我认为你可以对任何人列表这样做：

public ResponseMessage readAllSuppliers() 
    List<Suppliers> lstsuppliers = new ArrayList<Suppliers>();
    lstsuppliers = supplierDAO.getAllSuppliers();
    //ResponseMessage(code, message, list or object data)
    ResponseMessage rm = new ResponseMessage(123, "reading suppliers", lstsuppliers);
    return rm;

最后，在 WebService 客户端上获取类似这样的信息数据：

public void getSuppliers() 
    WebServiceResponse wsr = new WebServiceResponse();
    ResponseMessage rm = wsr.readAllSuppliers();
    System.out.println("CODE: " + rm.getCode()); //CODE: 123
    System.out.println("MESSAGE: " + rm.getMessage()); //MESSAGE: reading suppliers
    for (Suppliers data : rm.getLstData()) 
       System.out.println("SUPPLIER INFO: " + data.getFullName()); 
    
    //SUPPLIER INFO: Name1 Surname1
    //SUPPLIER INFO: Name2 Surname2
    //SUPPLIER INFO: Name3 Surname3

希望你能帮到我

【问题讨论】：

查看构建器模式：en.wikipedia.org/wiki/Builder_pattern

另一种方法是发送HashMap 和keys，即types of list (user,customers) 和corresponding lists 作为values。您可以只有一个以HashMap 作为参数的构造函数。在您的构造函数中，您可以通过从地图获取代码来设置所有列表。由于HashMap 操作为O(1)，因此对性能也没有太大影响。

【参考方案1】：

你只需要在你的ResponseMessage 声明之后添加<T> 来告诉Java 你想使用泛型。希望这可以帮助。请注意，它希望每个响应仅返回一种类型。如果您需要发送多个类型，最好使用Map 或Types 到Lists，而不是@v1shnu 提到的lstData。

public class ResponseMessage<T> implements Serializable 

    private final List<T> lstData;
    private final Integer code;
    private final String message;

    public ResponseMessage(Integer code, String message, List<T> lstData) 
        this.code = code;
        this.message = message;
        this.lstData = lstData;
    

您可以考虑为您的数据访问对象做同样的事情。

【讨论】：

我尝试过这种方式但不起作用，当我调用供应商方法时，会显示下一个错误：javax.xml.bind.JAXBException: class Supplier 或其任何超类已知这个上下文

得到下一个错误对我来说听起来像是进步！看看这个：***.com/questions/14057932/…

但是编码是 REST 并且我使用的是 SOAP，语法发生了变化，我无法适应它:(

【参考方案2】：

您可以创建一个HashMap，然后将其发送到ResponseMessage，如下所示：

Map<String,List<T>> listsMap = new HashMap<>();
listsMap.put("users",userDao.readAllUsers());
listsMap.put("customers",customerDao.readAllCustomers());
listsMap.put("suppliers",supplierDao.readAllSuppliers());

ResponseMessage rm = new ResponseMessage(123, "message", listsMap);

在您的ResponseMessage 类中，您可以添加如下构造函数：

public ResponseMessage (Integer code, String message,Map listsMap)
    this.code = code;
    this.message = message;
    this.listUsers = (List<Users>) listsMap.get("users");
    this.listCustomers = (List<Customers>) listsMap.get("customers");
    this.listSuppliers = (List<Suppliers>) listsMap.get("suppliers");

【讨论】：

出现下一个错误：java.util.List is an interface, and JAXB can't handle interfaces. this problem is related to the following location: at java.util.List at public java.util.Map ResponseMessage.getListsMap()