运行EJB示例项目时出现错误500:java.lang.NullPointerException

我是EJB新手，因此我执行了一个示例EJB项目，如教程中所示

以下是豆子的外观：

Converter.java

package converter.ejb;

import java.math.BigDecimal;
import javax.ejb.Remote;

@Remote
public interface Converter {
    public BigDecimal dollarToYen(BigDecimal dollars);
    public BigDecimal yenToEuro(BigDecimal yen);
}

package converter.ejb;

import java.math.BigDecimal;
import javax.ejb.LocalBean;
import javax.ejb.Stateless;

@Stateless
public class ConverterBean {

    private BigDecimal yenRate = new BigDecimal("115.3100");
    private BigDecimal euroRate = new BigDecimal("0.0071");

    public BigDecimal dollarToYen(BigDecimal dollars) {
        BigDecimal result = dollars.multiply(yenRate);
        return result.setScale(2, BigDecimal.ROUND_UP);
    }

    public BigDecimal yenToEuro(BigDecimal yen) {
        BigDecimal result = yen.multiply(euroRate);
        return result.setScale(2, BigDecimal.ROUND_UP);
    }
}

package converter.ejb;

import java.math.BigDecimal;
import javax.ejb.EJB;

public class ConverterClient {

    @EJB
    private static Converter converter;

    public ConverterClient(String[] args) {
    }

    public static void main(String[] args) {
        ConverterClient client = new ConverterClient(args);
        client.doConversion();
    }

    public void doConversion() {
        try {
            BigDecimal param = new BigDecimal("100.00");
            BigDecimal yenAmount = converter.dollarToYen(param);

            System.out.println("$" + param + " is " + yenAmount
                    + " Yen.");
            BigDecimal euroAmount = converter.yenToEuro(yenAmount);
            System.out.println(yenAmount + " Yen is " + euroAmount
                    + " Euro.");

            System.exit(0);
        } catch (Exception ex) {
            System.err.println("Caught an unexpected exception!");
            ex.printStackTrace();
        }
    }
}

ConverterBean.java

package converter.ejb;

import java.math.BigDecimal;
import javax.ejb.Remote;

@Remote
public interface Converter {
    public BigDecimal dollarToYen(BigDecimal dollars);
    public BigDecimal yenToEuro(BigDecimal yen);
}

package converter.ejb;

import java.math.BigDecimal;
import javax.ejb.LocalBean;
import javax.ejb.Stateless;

@Stateless
public class ConverterBean {

    private BigDecimal yenRate = new BigDecimal("115.3100");
    private BigDecimal euroRate = new BigDecimal("0.0071");

    public BigDecimal dollarToYen(BigDecimal dollars) {
        BigDecimal result = dollars.multiply(yenRate);
        return result.setScale(2, BigDecimal.ROUND_UP);
    }

    public BigDecimal yenToEuro(BigDecimal yen) {
        BigDecimal result = yen.multiply(euroRate);
        return result.setScale(2, BigDecimal.ROUND_UP);
    }
}

package converter.ejb;

import java.math.BigDecimal;
import javax.ejb.EJB;

public class ConverterClient {

    @EJB
    private static Converter converter;

    public ConverterClient(String[] args) {
    }

    public static void main(String[] args) {
        ConverterClient client = new ConverterClient(args);
        client.doConversion();
    }

    public void doConversion() {
        try {
            BigDecimal param = new BigDecimal("100.00");
            BigDecimal yenAmount = converter.dollarToYen(param);

            System.out.println("$" + param + " is " + yenAmount
                    + " Yen.");
            BigDecimal euroAmount = converter.yenToEuro(yenAmount);
            System.out.println(yenAmount + " Yen is " + euroAmount
                    + " Euro.");

            System.exit(0);
        } catch (Exception ex) {
            System.err.println("Caught an unexpected exception!");
            ex.printStackTrace();
        }
    }
}

ConverterClient.java

package converter.ejb;

import java.math.BigDecimal;
import javax.ejb.Remote;

@Remote
public interface Converter {
    public BigDecimal dollarToYen(BigDecimal dollars);
    public BigDecimal yenToEuro(BigDecimal yen);
}

package converter.ejb;

import java.math.BigDecimal;
import javax.ejb.LocalBean;
import javax.ejb.Stateless;

@Stateless
public class ConverterBean {

    private BigDecimal yenRate = new BigDecimal("115.3100");
    private BigDecimal euroRate = new BigDecimal("0.0071");

    public BigDecimal dollarToYen(BigDecimal dollars) {
        BigDecimal result = dollars.multiply(yenRate);
        return result.setScale(2, BigDecimal.ROUND_UP);
    }

    public BigDecimal yenToEuro(BigDecimal yen) {
        BigDecimal result = yen.multiply(euroRate);
        return result.setScale(2, BigDecimal.ROUND_UP);
    }
}

package converter.ejb;

import java.math.BigDecimal;
import javax.ejb.EJB;

public class ConverterClient {

    @EJB
    private static Converter converter;

    public ConverterClient(String[] args) {
    }

    public static void main(String[] args) {
        ConverterClient client = new ConverterClient(args);
        client.doConversion();
    }

    public void doConversion() {
        try {
            BigDecimal param = new BigDecimal("100.00");
            BigDecimal yenAmount = converter.dollarToYen(param);

            System.out.println("$" + param + " is " + yenAmount
                    + " Yen.");
            BigDecimal euroAmount = converter.yenToEuro(yenAmount);
            System.out.println(yenAmount + " Yen is " + euroAmount
                    + " Euro.");

            System.exit(0);
        } catch (Exception ex) {
            System.err.println("Caught an unexpected exception!");
            ex.printStackTrace();
        }
    }
}

我有一个web客户端，它是一个JSP页面：converterweb.JSP

<%@ page import="converter.ejb.Converter,
            java.math.*, javax.naming.*"%>    
 <%!
    private Converter converter = null;
    public void jspInit() {
        try {
            InitialContext ic = new InitialContext();
            converter = (Converter)
                    ic.lookup(Converter.class.getName());
        } catch (Exception ex) {
            System.out.println("Couldn’t create converter bean."+
                    ex.getMessage());
        }
    }
        public void jspDestroy() {
        converter = null;
    }
%>
<html>
    <head>
        <title>Converter</title>
    </head>

    <body bgcolor="white">
        <h1>Converter</h1>
        <hr>
        <p>Enter an amount to convert:</p>
        <form method="get">
            <input type="text" name="amount" size="25">
            <br>
            <p>
            <input type="submit" value="Submit">
            <input type="reset" value="Reset">
        </form>

        <%
            String amount = request.getParameter("amount");
            if ( amount != null && amount.length() > 0 ) {
                BigDecimal d = new BigDecimal(amount);

                BigDecimal yenAmount = converter.dollarToYen(d);
        %>
        <p>
        <%= amount %> dollars are  <%= yenAmount %>  Yen.
        <p>
        <%
                BigDecimal euroAmount =
                        converter.yenToEuro(yenAmount);
        %>
        <%= amount %> Yen are <%= euroAmount %>  Euro.
        <%
            }
        %>
    </body>
</html>

---

您的代码充满了错误：

• EJB依赖项注入适用于容器管理的组件。您的ConverterClient上没有注释（我假设您没有在xml描述符中进行任何额外的EJB配置）。所以容器并没有意识到这一点，也不能进行注射
• 您的转换器被声明为静态。这是行不通的
• 您正试图通过远程接口访问声明为@LocalBean的bean（这意味着它不公开任何接口视图）。这也行不通。尝试直接使用ConverterBean，或者避免使用@LocalBean，而是使用@Remote（Converter.class）

---

也许我错过了什么。希望这能有所帮助。

您从哪里获得NPE？我假设在您调用

converter.dollarToYen（param）

的行中，对吗？@Yevgeniy我不确定NPE在哪里。Websphere错误日志指向Java文件，该文件是JSP文件的转换。我的JSP是converterweb.JSP，它指向converterweb.java的第118行，我无法打开该行。如果您不发布跟踪错误日志，很难“猜测”您的问题是什么。错误500表示您有服务器端错误。请粘贴在服务器日志中发现的错误。我想这不是OP所问问题的解释。@Andrey由于我是EJB新手，所以我一直遵循本教程，并尝试使用它@Rajath本教程中有一些要点与您的文章不同：-ConverterBean没有用@LocalBean；-ConverterBean实现转换器接口。“如果你修好了，我想它应该会工作的。”安德烈·波伦谢谢你指出它！已更正，但仍不起作用。@Rajath您是否根据更改更新了帖子？我这样问是因为您删除了LocalBean注释，但仍然没有使ConverterBean实现转换器。您应该在ConverterBean上添加额外的注释远程（Converter.class），或者让ConverterBean实现Converter。我想这可能是你问题的原因。