[英]Cant instantiate class when using managed property
我正在學習Java 6 EE,並且有一個簡單的Web應用程序。
我有使用CurrencyManager
類的UserBean
類。 CurrencyManager
是應用程序范圍的,並且是托管bean。 UserBean
是受管bean,並且具有會話作用域。
這是我的UserBean
:
@ManagedBean
@SessionScoped
public class UserBean implements Serializable{
private String username;
private ArrayList<Money> ownedMoney;
private CurrencyManager currencyManager;
private BigDecimal credits;
public UserBean() {
currencyManager = new CurrencyManager();
username = "User";
ownedMoney = new ArrayList<>();
ownedMoney.add(new Money(new BigDecimal(15000), currencyManager.getCurrency("CZK")));
ownedMoney.add(new Money(new BigDecimal(100), currencyManager.getCurrency("USD")));
credits = new BigDecimal(150);
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public BigDecimal getCredits() {
return credits;
}
public void setCredits(BigDecimal credits) {
this.credits = credits;
}
public ArrayList<Money> getOwnedMoney() {
return ownedMoney;
}
public void setOwnedMoney(ArrayList<Money> ownedMoney) {
this.ownedMoney = ownedMoney;
}
public CurrencyManager getCurrencyManager() {
return currencyManager;
}
public void setCurrencyManager(CurrencyManager currencyManager) {
this.currencyManager = currencyManager;
}
}
這是我的CurrencyManager
:
@ManagedBean(name = "currencyManager")
@ApplicationScoped
public class CurrencyManager {
private HashMap<String, Currency> currencies;
public CurrencyManager() {
this.currencies = new HashMap<>();
currencies.put("CZK", new Currency("CZK", new BigDecimal("0.0503")));
currencies.put("GBP", new Currency("GBP", new BigDecimal("0.59")));
currencies.put("EUR", new Currency("EUR", new BigDecimal("1.38")));
currencies.put("USD", new Currency("USD", new BigDecimal("1.0")));
}
public Currency getCurrency(String name){
return currencies.get(name);
}
public java.util.Collection<Currency> getCurrencies() {
return currencies.values();
}
public void setCurrencies(HashMap<String, Currency> currencies) {
this.currencies = currencies;
}
}
我發布的代碼按原樣工作正常。 但是我不想在UserBean
類中實例化CurrencyManager
這就是為什么我將其設置為ApplicationScoped,因為它應該一直可用。
如果刪除實例化( UserBean
構造函數的第一行)並將聲明更改為:
@ManagedProperty(value = "#{currencyManager}")
private CurrencyManager currencyManager;
然后查詢UserBean
ownedMoney
屬性的第一頁將引發javax.servlet.ServletException: Cant instantiate class: model.UserBean.
與NullPointerException
根本原因有關。 GlassFish日志顯示,當我在currencyManager
上調用getCurrency
時,在UserBean
構造函數中發生了NullPtr:
ownedMoney.add(new Money(new BigDecimal(15000), currencyManager.getCurrency("CZK")));
你能告訴我我做錯了嗎?
我只是遇到了同樣的問題,並且偶然發現,如果我嘗試使用firefox(實際上是Linux下的icedove),它是行不通的,但是如果我嘗試使用eclipse內置瀏覽器,它將很好地工作。
即使這樣,這對我來說也沒有意義,您是否已經嘗試過使用其他瀏覽器?
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