我试图实现一个简单的购物车系统的网站.我正在使用Spring框架和Rest API来为网站做后端.购物车必须能够从文件中消毒和go 菌，以便用户可以注销和返回，仍然保留他们的购物车项目.在我的例子中，购物车中充满了Need对象，其功能与放入购物车中的物品相似.
起初，我try 用这种方式来实现我的购物车:
package com.ufund.api.ufundapi.model;
import java.util.ArrayList;
import java.util.logging.Logger;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
/**
* Represents a Cart entity
*/
@JsonPropertyOrder({ "id", "needs"})
public class Cart {
@SuppressWarnings("unused")
private static final Logger LOG = Logger.getLogger(Cart.class.getName());
// Package private for tests
static final String STRING_FORMAT = "Cart [id=%d, needsArr=%s]";
@JsonProperty("id") private int id;
@JsonProperty("needs") private ArrayList<Need> needs;
/**
* Create a cart with the given id and map of needs.
* @param id the id of the cart
* @param needs the list of needs in the cart.
*
* {@literal @} JsonProperty is used in serialization and deserialization
* of the JSON object to the Java object in mapping the fields. If a field
* is not provided in the JSON object, the Java field gets the default Java
* value, i.e. 0 for int.
*/
public Cart(@JsonProperty("id") int id, @JsonProperty("needs") ArrayList<Need> needs) {
this.id = id;
this.needs = needs;
}
/**
* Creates and empty cart with the given id.
* @param id the id of the cart.
*/
public Cart(int id) {
this.id = id;
this.needs = new ArrayList<Need>();
}
/**
* Retrieves the id of the cart
* @return the id of the cart
*/
public int getId() {return id;}
/**
* Retrieves the needs in the cart
* @return An array of needs in the cart
*/
public Need[] getneeds() {
return (Need[])(needs.toArray());
}
public Boolean addNeed(Need n) {
for (Need need: needs)
{
if(n.getId() == need.getId()) { return false; }
}
needs.add(n);
return true;
}
public Boolean updateNeed(Need n) {
for (Need need: needs)
{
if(n.getId() == need.getId())
{
need.setQuantity(n.getQuantity());
return true;
}
}
return false;
}
public Boolean deleteNeed(int id) {
for (Need need: needs)
{
if(id == need.getId())
{
return needs.remove(need);
}
}
return false;
}
public void checkout() {
needs.clear();
}
/**
* {@inheritDoc}
*/
@Override
public String toString(){
return String.format(STRING_FORMAT, id, needs.toString());
}
}
错误:class [Ljava.lang.Object; cannot be cast to class [Lcom.ufund.api.ufundapi.model.Need; ([Ljava.lang.Object; is in module java.base of loader 'bootstrap'; [Lcom.ufund.api.ufundapi.model.Need; is in unnamed module of loader 'app') (through reference chain: com.ufund.api.ufundapi.model.Cart[0]->com.ufund.api.ufundapi.model.Cart["needs"])
这个错误很奇怪，因为Need类有独立的文件保存功能，工作得很好.我假设@ jsonProperty必须只允许私有数据类型，所以我转换并删除代码，使用私有数据类型String来消毒数据:
package com.ufund.api.ufundapi.model;
import java.util.ArrayList;
import java.util.logging.Logger;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
/**
* Represents a Cart entity
*
*/
@JsonPropertyOrder({ "id", "needsArr"})
public class Cart {
@SuppressWarnings("unused")
private static final Logger LOG = Logger.getLogger(Cart.class.getName());
// Package private for tests
static final String STRING_FORMAT = "Cart [id=%d, needsArr=%s]";
@JsonProperty("id") private int id;
@JsonProperty("needsArr") private String needsArr;
private ArrayList<int[]> needs;
/**
* Create a cart with the given id and map of needs.
* @param id the id of the cart
* @param needsArr the list of needs in the cart.
*
* {@literal @} JsonProperty is used in serialization and deserialization
* of the JSON object to the Java object in mapping the fields. If a field
* is not provided in the JSON object, the Java field gets the default Java
* value, i.e. 0 for int.
*/
public Cart(@JsonProperty("id") int id, @JsonProperty("needsArr") String needsArr) {
this.id = id;
needs = new ArrayList<int[]>();
this.needsArr = needsArr;
}
/**
* Creates and empty cart with the given id.
* @param id the id of the cart.
*/
public Cart(int id) {
this.id = id;
this.needs = new ArrayList<int[]>();
needsArr = "";
}
/**
* Retrieves the id of the cart
* @return the id of the cart
*/
public int getId() {return id;}
/**
* Retrieves the needs in the cart
* @return An array of needs in the cart
*/
public int[][] getneeds() {
return (int[][])(needs.toArray());
}
public Boolean addNeed(Need n) {
for (int[] need: needs)
{
if(n.getId() == need[0]) { return false; }
}
needs.add(new int[]{n.getId(),
n.getQuantity()});
return true;
}
public Boolean updateNeed(Need n) {
for (int[] need: needs)
{
if(n.getId() == need[0])
{
need[1] = n.getQuantity();
return true;
}
}
return false;
}
public Boolean deleteNeed(int id) {
for (int[] need: needs)
{
if(id == need[0])
{
return needs.remove(need);
}
}
return false;
}
public void checkout() {
needs.clear();
}
/**
* {@inheritDoc}
*/
@Override
public String toString(){
return String.format(STRING_FORMAT, id, needsArr);
}
}
错误:class [Ljava.lang.Object; cannot be cast to class [[I ([Ljava.lang.Object; and [[I are in module java.base of loader 'bootstrap') (through reference chain: com.ufund.api.ufundapi.model.Cart[0]->com.ufund.api.ufundapi.model.Cart["needs"])
这是没有意义的，因为我删除了@ JsonProperty的"needs"，并将其替换为"needsArr".
我决定删除一个只有两个类变量的实现，看看它是否是它.这个方法如果实现，将只在本地存储一个字符串来表示我的Needs数组，并且每次对Needs的操作完成时都必须转换为数组:
package com.ufund.api.ufundapi.model;
import java.util.ArrayList;
import java.util.logging.Logger;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
/**
* Represents a Cart entity
*
*/
@JsonPropertyOrder({ "id", "needs"})
public class Cart {
@SuppressWarnings("unused")
private static final Logger LOG = Logger.getLogger(Cart.class.getName());
// Package private for tests
static final String STRING_FORMAT = "Cart [id=%d, needs=%s]";
@JsonProperty("id") private int id;
@JsonProperty("needs") private String needs;
/**
* Create a cart with the given id and map of needs.
* @param id the id of the cart
* @param needs the list of needs in the cart.
*
* {@literal @} JsonProperty is used in serialization and deserialization
* of the JSON object to the Java object in mapping the fields. If a field
* is not provided in the JSON object, the Java field gets the default Java
* value, i.e. 0 for int.
*/
public Cart(@JsonProperty("id") int id, @JsonProperty("needs") String needs) {
this.id = id;
this.needs = needs;
}
/**
* Creates and empty cart with the given id.
* @param id the id of the cart.
*/
public Cart(int id) {
this.id = id;
this.needs = "[]";
}
/**
* Retrieves the id of the cart
* @return the id of the cart
*/
public int getId() {return id;}
/**
* Retrieves the needs in the cart
* @return An array of needs in the cart
*/
public int[][] getneeds() {
return (int[][])(decode().toArray());
}
public Boolean addNeed(Need n) {
ArrayList<int[]> needArr = decode();
for (int[] need: needArr)
{
if(n.getId() == need[0]) { return false; }
}
needArr.add(new int[]{n.getId(),
n.getQuantity()});
encode(needArr);
return true;
}
public Boolean updateNeed(Need n) {
ArrayList<int[]> needArr = decode();
for (int[] need: needArr)
{
if(n.getId() == need[0])
{
need[1] = n.getQuantity();
encode(needArr);
return true;
}
}
return false;
}
public Boolean deleteNeed(int id) {
ArrayList<int[]> needArr = decode();
for (int[] need: needArr)
{
if(id == need[0] && needArr.remove(need))
{
encode(needArr);
return true;
}
}
return false;
}
public void checkout() {
needs = "[]";
}
private void encode(ArrayList<int[]> needs) {
this.needs = "[]";
}
private ArrayList<int[]> decode() {
return new ArrayList<int[]>();
}
/**
* {@inheritDoc}
*/
@Override
public String toString(){
return String.format(STRING_FORMAT, id, needs);
}
}
再次出现错误:class [Ljava.lang.Object; cannot be cast to class [[I ([Ljava.lang.Object; and [[I are in module java.base of loader 'bootstrap') (through reference chain: com.ufund.api.ufundapi.model.Cart[0]->com.ufund.api.ufundapi.model.Cart["needs"])
我是如此困惑这个神秘的问题与需求变量，我试图只是删除它完全使购物车失go 功能.
package com.ufund.api.ufundapi.model;
import java.util.ArrayList;
import java.util.logging.Logger;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
/**
* Represents a Cart entity
*
*/
@JsonPropertyOrder({ "id"})//, "needs"})
public class Cart {
@SuppressWarnings("unused")
private static final Logger LOG = Logger.getLogger(Cart.class.getName());
// Package private for tests
static final String STRING_FORMAT = "Cart [id=%d]";//, needs=%s]";
@JsonProperty("id") private int id;
//@JsonProperty("needs") private String needs;
/**
* Create a cart with the given id and map of needs.
* @param id the id of the cart
* @param needs the list of needs in the cart.
*
* {@literal @} JsonProperty is used in serialization and deserialization
* of the JSON object to the Java object in mapping the fields. If a field
* is not provided in the JSON object, the Java field gets the default Java
* value, i.e. 0 for int.
*/
public Cart(@JsonProperty("id") int id) {//, @JsonProperty("needs") String needs) {
this.id = id;
//this.needs = needs;
}
/**
* Creates and empty cart with the given id.
* @param id the id of the cart.
*/
/*public Cart(int id) {
this.id = id;
this.needs = "[]";
}*/
/**
* Retrieves the id of the cart
* @return the id of the cart
*/
public int getId() {return id;}
/**
* Retrieves the needs in the cart
* @return An array of needs in the cart
*/
public int[][] getneeds() {
return (int[][])(decode().toArray());
}
public Boolean addNeed(Need n) {
ArrayList<int[]> needArr = decode();
for (int[] need: needArr)
{
if(n.getId() == need[0]) { return false; }
}
needArr.add(new int[]{n.getId(),
n.getQuantity()});
encode(needArr);
return true;
}
public Boolean updateNeed(Need n) {
ArrayList<int[]> needArr = decode();
for (int[] need: needArr)
{
if(n.getId() == need[0])
{
need[1] = n.getQuantity();
encode(needArr);
return true;
}
}
return false;
}
public Boolean deleteNeed(int id) {
ArrayList<int[]> needArr = decode();
for (int[] need: needArr)
{
if(id == need[0] && needArr.remove(need))
{
encode(needArr);
return true;
}
}
return false;
}
public void checkout() {
//needs = "[]";
}
private void encode(ArrayList<int[]> needs) {
//this.needs = "[]";
}
private ArrayList<int[]> decode() {
return new ArrayList<int[]>();
}
/**
* {@inheritDoc}
*/
@Override
public String toString(){
return String.format(STRING_FORMAT, id);//, needs);
}
}
错误:class [Ljava.lang.Object; cannot be cast to class [[I ([Ljava.lang.Object; and [[I are in module java.base of loader 'bootstrap') (through reference chain: com.ufund.api.ufundapi.model.Cart[0]->com.ufund.api.ufundapi.model.Cart["needs"])
这说不通啊我删除了所有需要类变量，对象映射器仍在try 实现它.有谁知道这是怎么发生的，以及我可以解决这个问题的可能方法吗？
如果它们是必要的，这里是将Carts写入文件的类和Need类:
package com.ufund.api.ufundapi.persistence;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Map;
import java.util.TreeMap;
import java.util.logging.Logger;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
import com.ufund.api.ufundapi.model.Cart;
import com.ufund.api.ufundapi.model.Need;
/**
* Implements the functionality for JSON file-based peristance for cart
*
* {@literal @}Component Spring annotation instantiates a single instance of this
* class and injects the instance into other classes as Carted
*/
@Component
public class CartFileDAO implements CartDAO {
@SuppressWarnings("unused")
private static final Logger LOG = Logger.getLogger(CartFileDAO.class.getName());
Map<Integer,Cart> cartPark; // Provides a local cache of the cartPark
// so that we don't need to read from the file
// each time
private ObjectMapper objectMapper; // Provides conversion between Cart
// objects and JSON text format written
// to the file
private String filename; // Filename to read from and write to
/**
* Creates a Cart File Data Access Object
*
* @param filename Filename to read from and write to
* @param objectMapper Provides JSON Object to/from Java Object serialization and deserialization
*
* @throws IOException when file cannot be accessed or read from
*/
public CartFileDAO(@Value("${cartPark.file}") String filename, ObjectMapper objectMapper) throws IOException {
this.filename = filename;
this.objectMapper = objectMapper;
load(); // load the cartPark from the file
}
/**
* Generates an array of {@linkplain Cart carts} from the tree map for any
* {@linkplain Cart carts}.
*
* @return The array of {@link Cart carts}, may be empty.
*/
private Cart[] getcartParkArray() { // if containsText == null, no filter
ArrayList<Cart> cartArrayList = new ArrayList<>();
for (Cart cart : cartPark.values()) {
cartArrayList.add(cart);
}
Cart[] cartArray = new Cart[cartArrayList.size()];
cartArrayList.toArray(cartArray);
return cartArray;
}
/**
* Saves the {@linkplain Cart carts} from the cartPark into the file as an array of JSON objects
*
* @return true if the {@link Cart carts} were written successfully
*
* @throws IOException when file cannot be accessed or written to
*/
private boolean save() throws IOException {
Cart[] CartArray = getcartParkArray();
// Serializes the Java Objects to JSON objects into the file
// writeValue will thrown an IOException if there is an issue
// with the file or reading from the file
objectMapper.writeValue(new File(filename),CartArray);
return true;
}
/**
* Loads {@linkplain Cart carts} from the JSON file into the cartPark
* <br>
* Also sets next id to one more than the greatest id found in the file
*
* @return true if the file was read successfully
*
* @throws IOException when file cannot be accessed or read from
*/
private boolean load() throws IOException {
cartPark = new TreeMap<>();
// Deserializes the JSON objects from the file into an array of car
// readValue will throw an IOException if there's an issue with the file
// or reading from the file
Cart[] CartArray = objectMapper.readValue(new File(filename),Cart[].class);
// Add each Cart to the tree map and keep track of the greatest id
for (Cart Cart : CartArray) {
cartPark.put(Cart.getId(),Cart);
}
return true;
}
/**
** {@inheritDoc}
*/
@Override
public Need[] getCart(int id, NeedDAO needDAO) throws IOException {
synchronized(cartPark) {
Cart cart = cartPark.get(id);
if(cart == null)
{
return null;
}
int[][] needs = cart.getneeds();
Need[] needsArr = new Need[needs.length];
for (int i = 0; i < needs.length; i++) {
Need need = needDAO.getNeed(needs[i][0]);
need.setQuantity(needs[i][1]);
needsArr[i] = need;
}
return needsArr;
}
}
/**
** {@inheritDoc}
*/
@Override
public Boolean createCart(int id) throws IOException {
synchronized(cartPark) {
if(cartPark.containsKey(id)) {
return false;
}
Cart newCart = new Cart(id);
cartPark.put(newCart.getId(),newCart);
save(); // may throw an IOException
return true;
}
}
/**
** {@inheritDoc}
*/
@Override
public Boolean addNeed(int cId, int nId, NeedDAO needDAO) throws IOException {
synchronized(cartPark) {
Need need = needDAO.getNeed(nId);
if(need == null) {
return false;
}
return cartPark.get(cId).addNeed(need) && save();
}
}
/**
** {@inheritDoc}
*/
@Override
public Boolean updateNeed(int id, Need n) throws IOException {
synchronized(cartPark) {
Cart cart = cartPark.get(id);
if(cart == null) {
return false;
}
return cart.updateNeed(n) && save();
}
}
/**
** {@inheritDoc}
*/
@Override
public Boolean deleteNeed(int cId, int nId) throws IOException {
synchronized(cartPark) {
Cart cart = cartPark.get(cId);
if(cart == null) {
return false;
}
return cart.deleteNeed(nId) && save();
}
}
/**
** {@inheritDoc}
*/
@Override
public Boolean checkout(int id) throws IOException {
synchronized(cartPark) {
Cart cart = cartPark.get(id);
if(cart == null) {
return false;
}
cart.checkout();
return save();
}
}
/**
** {@inheritDoc}
*/
@Override
public Boolean deleteCart(int id) throws IOException {
synchronized(cartPark) {
return cartPark.remove(id) != null && save();
}
}
}
package com.ufund.api.ufundapi.model;
import java.util.logging.Logger;
import com.fasterxml.jackson.annotation.JsonProperty;
/**
* Represents a Need entity
*
*/
public class Need {
@SuppressWarnings("unused")
private static final Logger LOG = Logger.getLogger(Need.class.getName());
// Package private for tests
static final String STRING_FORMAT = "Need [id=%d, name=%s, type=%s, cost=%d, quantity=%d]";
@JsonProperty("id") private int id;
@JsonProperty("name") private String name;
@JsonProperty("type") private String type;
@JsonProperty("cost") private int cost;
@JsonProperty("quantity") private int quantity;
/**
* Create a need with the given id, name, type, cost, and quantity.
* @param id The id of the need
* @param name The name of the need
* @param type The type of the type
* @param cost The name of the cost
* @param quantity The name of the quantity
*
* {@literal @}JsonProperty is used in serialization and deserialization
* of the JSON object to the Java object in mapping the fields. If a field
* is not provided in the JSON object, the Java field gets the default Java
* value, i.e. 0 for int
*/
public Need(@JsonProperty("id") int id, @JsonProperty("name") String name, @JsonProperty("type") String type,
@JsonProperty("cost") int cost, @JsonProperty("quantity") int quantity) {
this.id = id;
this.name = name;
this.cost = cost;
this.quantity = quantity;
this.type = type;
}
/**
* Retrieves the id of the need
* @return The id of the need
*/
public int getId() {return id;}
/**
* Sets the name of the need - necessary for JSON object to Java object deserialization
* @param name The name of the need
*/
public void setName(String name) {this.name = name;}
/**
* Retrieves the name of the need
* @return The name of the need
*/
public String getName() {return name;}
/**
* Retrieves the type of the need
* @return The type of the need
*/
public String getType() {return type;}
/**
* Sets the type of the need - necessary for JSON object to Java object deserialization
* @param name The type of the need
*/
public void setType(String type) {this.type = type;}
/**
* Retrieves the cost of the need
* @return The cost of the need
*/
public int getCost() {return cost;}
/**
* Retrieves the quantity of the need
* @return The quantity of the need
*/
public int getQuantity() {return quantity;}
/**
* Sets the cost of the need - necessary for JSON object to Java object deserialization
* @param cost The cost of the need
*/
public void setCost(int cost) {this.cost = cost;}
/**
* Sets the quantity of the need - necessary for JSON object to Java object deserialization
* @param quantity The quantity of the need
*/
public void setQuantity(int quantity) {this.quantity = quantity;}
/**
* {@inheritDoc}
*/
@Override
public String toString() {
return String.format(STRING_FORMAT,id,name,type,cost,quantity);
}
}