我正在写我的最后一个java作业（Yayy！ - 感谢所有帮助我完成其他工作的人）。在这一个中，我必须编写一个servlet，它接受年龄，婚姻状况，房屋收入和孩子数量，转到数据库，然后将更新的平均值返回给用户。但是，我遇到了这个 stacktrace：
java.lang.NoClassDefFoundError: HouseSurvey$SurveyResults
at HouseSurvey.doPost(HouseSurvey.java:23)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.servlets.InvokerServlet.serveRequest(InvokerServlet.java:419)
at org.apache.catalina.servlets.InvokerServlet.doPost(InvokerServlet.java:169)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:868)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:663)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:80)
at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:684)
at java.lang.Thread.run(Unknown Source)
Caused by: java.lang.ClassNotFoundException: HouseSurvey$SurveyResults
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1338)
at org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1187)
... 21 more
在过去，我已经犯了过多代码，没有足够的代码等等。我为我的新生事道歉。这是我写的课程：
import java.text.DecimalFormat;
import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;
public class HouseSurvey extends HttpServlet {
private final static String SURVEY_FILE = "HouseSurvey.dat";
SurveyResults results;
Household h;
DecimalFormat form = new DecimalFormat("#,###,#00.00");
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
PrintWriter out = response.getWriter(); //make a printwriter to print the page
File survey = new File(SURVEY_FILE);
if (!survey.exists()) //check to see if the file exists
results = new SurveyResults();
else { //If the file exists, read it the latest survey tallies
try {
ObjectInputStream ips = new ObjectInputStream(new FileInputStream(survey));
results = (SurveyResults) ips.readObject(); //read the file into 'results'
ips.close(); //close the input stream
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (FileNotFoundException f) {
f.printStackTrace();
} catch (IOException ioe) {
ioe.printStackTrace();
}
}
int ageValue = Integer.parseInt(request.getParameter("age")),
childValue = Integer.parseInt(request.getParameter("children"));
double incomeValue = Double.parseDouble(request.getParameter("income"));
Boolean marriedValue;
if (request.getParameter("status") == "married") {
marriedValue = true;
} else {
marriedValue = false;
}
Household h = new Household(ageValue, childValue, incomeValue, marriedValue);
results.totalResults(h);
//Write results to disk.
try {
ObjectOutputStream ops = new ObjectOutputStream(new FileOutputStream(survey));
ops.writeObject(results);
ops.flush();
ops.close();
} catch (IOException ioe) {
ioe.printStackTrace();
}
response.setContentType("text/html"); //contnent type for the responding webpage
out.println("<html>\n" +
"<head><title>Thanks!</tile></head>" +
"<body>" +
" <h1 style='text-align:center'>RRC BIT Department - Household Survey</h1>" +
" <hr><br/>" +
" <h2 style='text-align:center'>Up to Date Survey Results</h2>" +
" <h4 style='left-margin:200px'>Average Age: " + results.getAvgAge() +
" <h4 style='left-margin:200px'>Average Number of Children: " + results.getAvgKids() +
" <h4 style='left-margin:200px'>Average Number of Married Respondents: " + results.getAvgKids() +
" <h4 style='left-margin:200px'>Average Number of Single Respondents: " + results.getTotalSingle() +
" <h4 style='left-margin:200px'>Average Income: " + results.getAvgIncome());
}
private class Household {
private int age, children;
private double income;
private boolean married = false;
/**
* Method: Household
* Constructor
*
* @ param age - age of person surveyed:int
* @ param children - number of children person surveyed has:int
* @ param married - true or false, used to determine married or single:boolean
* @ param income - the family income of the person surveyed:double
*/
private Household(int age, int children, double income, boolean married) {
this.age = age;
this.children = children;
this.income = income;
this.married = married;
}
//Getters
private int getAge() {
return age;
}
private int getChildren() {
return children;
}
private double getIncome() {
return income;
}
private boolean getMarried() {
return married;
}
}
private class SurveyResults implements Serializable {
private double totalAge, totalChildren, totalMarried, totalSingle, totalIncome;
/**
* Method: SurveyResults
* Used for totals
*
* @ param h - Household object created above:Household
*/
private void totalResults(Household h) {
if (h.getMarried()) totalMarried += 1;
else totalSingle += 1;
totalAge += h.getAge();
totalChildren += h.getChildren();
totalIncome += h.getIncome();
}
private double getTotalHouseholds() {
return totalSingle + totalMarried;
}
private double getAvgAge() {
return totalAge / getTotalHouseholds();
}
private double getAvgKids() {
return totalChildren / getTotalHouseholds();
}
private double getTotalMarried() {
return totalMarried;
}
private double getTotalSingle() {
return totalSingle;
}
private double getAvgIncome() {
return totalIncome / getTotalHouseholds();
}
}
}
我觉得它非常接近，所以我去问我的导师。他看了大约20分钟，他无法理解。
我知道你们这些人非常聪明（尤其是当涉及到东西时），所以如果你们中的任何一个人可以花一点时间帮助一个兄弟出去.......
答案 0 :(得分：9)
看起来您没有上传所有已编译的.class文件。确保您不仅上传HouseSurvey.class，还要上传编译器生成的所有其他.class文件。在您的情况下，似乎缺少HouseSurvey$SurveyResults.class。
答案 1 :(得分：2)
java.lang.NoClassDefFoundError: HouseSurvey$SurveyResults
我建议为您的Java类创建一个包。 Tomcat对默认包中的.class文件不太友好。
您应该创建一个WAR文件并将其部署到Tomcat / webapps目录。不要把你的东西放进ROOT。
我还建议您不要将所有这些代码都压缩到servlet类中。如果你这样做，你不能在没有Tomcat的情况下测试或调试它。 servlet应该做的很少：监听HTTP请求，验证和绑定输入参数，调用其他类的方法来完成工作，然后将响应打包成适当的输出格式。而已。其他课程应该是繁重的工作。 Servlet是HTTP侦听器。
将您的问题分解成更小，更小的部分，您可以单独测试。
例如，在servlet外部的类中进行数据库交互。彻底测试并放在一边。
答案 2 :(得分：0)
将SurveyResults类公开。 readObject（）方法需要找到SurveyResult的定义。并且该类应该（很可能）是静态的。