我正在學習Java 6 EE,並且我有一個簡單的Web應用程序。我的UserBean
類使用CurrencyManager
類。 CurrencyManager
是應用程序作用域,是一個託管bean。 UserBean
是託管bean和會話範圍。使用託管屬性時無法實例化類
這裏是我的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;
}
}
在這裏,我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;
}
}
我張貼的作品罰款是代碼。但是我不想在我的UserBean
類中實例化CurrencyManager
- 這就是爲什麼我將其設爲ApplicationScoped的原因,因爲它應該始終可用。
如果我刪除實例化(在UserBean
構造第一線)和改變聲明:
@ManagedProperty(value = "#{currencyManager}")
private CurrencyManager currencyManager;
然後,查詢在UserBean
ownedMoney
財產與NullPointerException
根源拋出javax.servlet.ServletException: Cant instantiate class: model.UserBean.
的第一頁。 GlassFish的日誌表明,NullPtr在UserBean
構造時,當我打電話getCurrency
上currencyManager
,在這裏:
ownedMoney.add(new Money(new BigDecimal(15000), currencyManager.getCurrency("CZK")));
你能告訴我什麼,我做錯了什麼?