Question

设置：Windows 10 Pro 64位，IntelliJ IDEA 2018，JBoss WebServer

尽管通过研究和大量阅读，我对Java和JSP还是陌生的，我能够提出以下代码，该代码实现了Digital Persona库，以通知用户扫描仪是否已连接到他们的计算机： / p>

package com.digitalpersona.sample;

import com.digitalpersona.onetouch.DPFPGlobal;
import com.digitalpersona.onetouch.readers.DPFPReaderDescription;
import com.digitalpersona.onetouch.readers.DPFPReadersCollection;

public class ListReaders {
    public static String readerStatus() {
        String response = "";

        DPFPReadersCollection readers = DPFPGlobal.getReadersFactory().getReaders();
        if (readers == null || readers.size() == 0) {
            response = "There are no readers available.";
        }

        for (DPFPReaderDescription readerDescription : readers)
            response = readerDescription.getSerialNumber();

        return response;
    }
}

当我在IntelliJ上独立运行时，上面的代码可以正常工作，但是从JSP文件调用readerStatus（）方法时遇到麻烦。当我尝试这个：

<%@ page import="com.digitalpersona.sample.*" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>List Readers</title>
</head>
<body>
<%
    ListReaders deviceStatus = new ListReaders();
    out.println(deviceStatus);
%>
</body>
</html>

我明白了：

com.digitalpersona.sample.ListReaders@133d1476

或

com.digitalpersona.sample.ListReaders@71f2d51b

或

com.digitalpersona.sample.ListReaders@1c272943

基本上，后8个字符会不断变化。而当我尝试这样做时：

<%@ page import="com.digitalpersona.sample.*" %>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>List Readers</title>
</head>
<body>
<%
    ListReaders deviceStatus = new ListReaders();
    String responseMessage = deviceStatus.readerStatus();
    out.println(responseMessage);
%>
</body>
</html>

结果是这样的：

Error processing request
Context Path:/HelloWorld_war_exploded
Servlet Path:/listreaders.jsp
Path Info:null
Query String:null
Stack Trace:
javax.servlet.ServletException: java.lang.NoSuchMethodError: com.digitalpersona.sample.ListReaders.readerStatus()Ljava/lang/String;
    at org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:889)
    at org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:818)
    at org.apache.jsp.listreaders_jsp._jspService(listreaders_jsp.java:118)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:433)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:403)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:347)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
    at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85)
    at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
    at io.undertow.jsp.JspFileHandler.handleRequest(JspFileHandler.java:32)
    at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
    at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
    at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
    at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
    at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
    at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
    at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
    at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at org.wildfly.extension.undertow.deployment.GlobalRequestControllerHandler.handleRequest(GlobalRequestControllerHandler.java:68)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:292)
    at io.undertow.servlet.handlers.ServletInitialHandler.access$100(ServletInitialHandler.java:81)
    at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:138)
    at io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:135)
    at io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48)
    at io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43)
    at org.wildfly.extension.undertow.security.SecurityContextThreadSetupAction.lambda$create$0(SecurityContextThreadSetupAction.java:105)
    at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)
    at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)
    at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)
    at org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1508)
    at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:272)
    at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81)
    at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:104)
    at io.undertow.server.Connectors.executeRootHandler(Connectors.java:326)
    at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:812)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.lang.NoSuchMethodError: com.digitalpersona.sample.ListReaders.readerStatus()Ljava/lang/String;
    at org.apache.jsp.listreaders_jsp._jspService(listreaders_jsp.java:101)
    ... 45 more

有人可以帮助我从以下位置获取正确的输出吗？

return response;

谢谢。

Answer 1

请原谅我发帖，我的XP太少了，不能发表评论。

您没有类toString()的用户覆盖的ListReaders方法。因此，java将使用其内置方法来显示com.digitalpersona.sample.ListReaders@133d1476

@Override
public String toString() { 
    return "<Your values here>";
}

从JSP文件调用Java方法

1 个答案: