Java 运行时 ClassNotFoundException

Question

只是对我遇到的一个奇怪的运行时错误有疑问。我正在使用一个 JSON 服务器，该服务器在外部源提示时以 JSON 对象响应。然而，就目前而言，我只是想在发送之前启动并运行 JSON 对象。我的代码在未指定任何类路径的情况下进行编译，但在运行时，它会抛出一个 NoClassDefFoundError，如下所示:

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/lang/exception/NestableRuntimeException
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClassCond(ClassLoader.java:631)
at java.lang.ClassLoader.defineClass(ClassLoader.java:615)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:141)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:283)
at java.net.URLClassLoader.access$000(URLClassLoader.java:58)
at java.net.URLClassLoader$1.run(URLClassLoader.java:197)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
at ExampleServer.sendData(ExampleServer.java:76)
at ExampleServer.runServer(ExampleServer.java:30)
at ExampleServer.main(ExampleServer.java:15)
   Caused by: java.lang.ClassNotFoundException: org.apache.commons.lang.exception.NestableRuntimeException
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
at java.lang.ClassLoader.loadClass(ClassLoader.java:247)
... 15 more

我的代码如下:

import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
import java.lang.*;
import net.sf.json.*;

public class ExampleServer{

private DataOutputStream output;
private DataInputStream input;
private ServerSocket server;
private Socket connection;

public static void main(String[] args){
    new ExampleServer().runServer();
}

public void ExampleServer(){
    System.out.println("Server object created");
}

public void runServer(){
    try{
        server = new ServerSocket(12345,100);
        while(true){
            try{
                waitForConnection();
                getStreams();
                processConnection();
                sendData("Text");
            } catch(Exception e){
                System.out.println("Server Terminated Exception.");
            } finally {
                closeConnection();
            }
        }
    } catch(Exception e){
        e.printStackTrace();
    }
}

private void waitForConnection(){
    try{
        System.out.println("Waiting for connection.");
        connection = server.accept();
        System.out.println("Connection received from " + connection.getInetAddress().getHostName());
    } catch (IOException e){
        System.out.println(e);
    }
}

private void getStreams() throws IOException{
    output = new DataOutputStream(connection.getOutputStream());
    input = new DataInputStream(connection.getInputStream());
    System.out.println("Got streams");
}

private void processConnection() throws IOException{
    sendData("This is a test message");
}

private void closeConnection(){
    try{
        if(output != null && connection != null){
            sendData("SEVER>>> TERMINATE");
            output.close();
            connection.close();
        }
    } catch (IOException e){
        e.printStackTrace();
    }
}

private void sendData(String message){
    try{
        JSONObject g = new JSONObject();
        g.put("message", message);
        System.out.println(g.toString());
    } catch (Exception e){
        System.out.println("Error writing object");
    }
}

并且 JSON 文件夹与 ExampleServer.java 位于同一目录中，JSON 类驻留在 net/sf/json 中，如我的导入中所指定。为什么直到运行时它才工作？我的类路径是否出于某种原因不正确？包含必要类路径的适当语法是什么？

提前致谢

Answer 1

来自 json-lib homepage :

Json-lib requires (at least) the following dependencies in your classpath:

1. jakarta commons-lang 2.5
2. jakarta commons-beanutils 1.8.0
3. jakarta commons-collections 3.2.1
4. jakarta commons-logging 1.1.1
5. ezmorph 1.0.6

您的实现编译仅表明编译器可以找到正确的类和方法。然而，这些类和方法的实现可能取决于其他库。

可以找到有关项目依赖项的更多信息here .