MVC SPRING - org.springframework.web.util.NestedServletException：请求处理失败;嵌套的例外是显示java.lang.NullPointerException

Question

我的HTTPStatus 500嵌套异常，并显示java.lang.NullPointerException
IM制作多币种转换我用来调试时，它来到这里的错误开始currencypojo.setAmount（BigDecimal.valueOf（的Integer.parseInt（（用request.getParameter（ “txtAmount”）））））;

MultiCurrencyController.java

package com.multicurrency; 

import java.math.BigDecimal; 

import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 

import org.springframework.web.servlet.ModelAndView; 
import org.springframework.web.servlet.mvc.AbstractController; 

public class MultiCurrencyController extends AbstractController{ 

    private MultiCurrencyPOJO currencypojo; 
    @Override 
    protected ModelAndView handleRequestInternal(HttpServletRequest request, 
      HttpServletResponse response) throws Exception { 
     currencypojo.setAmount(BigDecimal.valueOf(Integer.parseInt((request.getParameter("txtAmount"))))); 
     currencypojo.setCurrency(request.getParameter("currency")); 
     return new ModelAndView ("home","CurrencyInfo",currencypojo); 
    } 

    public void multiCurrencyPOJO(MultiCurrencyPOJO currencypojo){ 
     this.currencypojo=currencypojo; 
    } 
} 

MultiCurrencyPOJO.java

package com.multicurrency; 

import java.math.BigDecimal; 



public class MultiCurrencyPOJO { 
    private String currency; 
    private BigDecimal amount; 

    public String getCurrency() { 
     return currency; 
    } 
    public void setCurrency(String currency) { 
     this.currency = currency; 
    } 
    public BigDecimal getAmount() { 
     return amount; 
    } 
    public void setAmount(BigDecimal amount) { 
     this.amount = amount; 
    } 

    public static BigDecimal getExchangeRate(String currency) { 
     return null; 

    } 
} 

Answer 1

它是可能的参数txtAmount没有设置在HTTP请求。为了更准确地了解错误发生的位置，我建议将其分成与其他类型转换分开的一行，并明确检查它是否已设置。

例如：

String txtAmount = request.getParameter("txtAmount"); 
if (txtAmount == null) { 
    throw new IllegalArgumentException("Expected HTTP request parameter txtAmount not present"); 
} 

currencypojo.setAmount(BigDecimal.valueOf(Integer.parseInt((txtAmount)); 

（另外，我会质疑首先需要一个BigDecimal - 尤其是因为你从Integer转换，但是这不是你的问题的主题。）

Answer 2

哪里是你Object对MultiCurrencyPOJO

private MultiCurrencyPOJO currencypojo; 

确保当你有此对象及其intiali的实例在你对它们进行操作之前先进

默认情况下，私人objetcs被初始化为null，所以在空的任何操作将结束NPE