Question

我得到了带有嵌套异常的HttpStatus 500和java.lang.NullPointerException
我正在制作一个多货币转换器我曾经调试它到达这里时错误开始 currencypojo.setAmount（BigDecimal.valueOf（Integer.parseInt（（request.getParameter（“txtAmount”）））））; < / p>

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

可能没有在HTTP请求中设置参数txtAmount。为了更准确地说明错误发生的位置，我建议将其拆分为与类型转换的其余部分分开的一行，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，我首先要问BigDecimal - 尤其是因为您要从Integer转换它，但这不是{{1}}你问题的主题。）

Answer 2

你在哪里MultiCurrencyPOJO的对象

private MultiCurrencyPOJO currencypojo;

确保在对这些对象进行操作之前，您拥有此对象的实例并将其初始化。

默认情况下，私人objetcs会初始化为null，因此任何以null为单位的操作都将以NPE结尾

MVC SPRING - org.springframework.web.util.NestedServletException：请求处理失败;嵌套异常是java.lang.NullPointerException

2 个答案: