Java：ConnectException/无法找到或加载主类

Question

所以简而言之，我只是想获得一个小的工作骨架程序，我可以用它来了解 Http 通信并“感受”我的方式来弄清楚我最终需要什么来完成一个更大的程序我正在努力。这里的这个特定代码实际上只是 Apache 库中示例的切碎版本。我可以编译 Apache 网站上列出的示例，但它们运行不正常，出现“java.net.ConnectException”。我认为这与 Windows c 阻止这样的程序建立连接有关，并且我需要以管理员身份运行它。然后我尝试获取代码并将其放入可执行的 jar 文件中，但我得到了一个无法找到或加载主类的错误。我是白痴还是 Apache 库有点过时/不适合 Win 8/其他？

代码如下：

package NewProject;


import java.net.Socket;

import org.apache.http.ConnectionReuseStrategy;
import org.apache.http.HttpHost;
import org.apache.http.HttpResponse;
import org.apache.http.impl.DefaultBHttpClientConnection;
import org.apache.http.impl.DefaultConnectionReuseStrategy;
import org.apache.http.message.BasicHttpRequest;
import org.apache.http.protocol.HttpCoreContext;
import org.apache.http.protocol.HttpProcessor;
import org.apache.http.protocol.HttpProcessorBuilder;
import org.apache.http.protocol.HttpRequestExecutor;
import org.apache.http.protocol.RequestConnControl;
import org.apache.http.protocol.RequestContent;
import org.apache.http.protocol.RequestExpectContinue;
import org.apache.http.protocol.RequestTargetHost;
import org.apache.http.protocol.RequestUserAgent;
import org.apache.http.util.EntityUtils;

class NewProject
{
    public static void main(String[] args) throws Exception
    {
        HttpProcessor httpproc = HttpProcessorBuilder.create()
            .add(new RequestContent())
            .add(new RequestTargetHost())
            .add(new RequestConnControl())
            .add(new RequestUserAgent("Test/1.1"))
            .add(new RequestExpectContinue(true)).build();

        HttpRequestExecutor httpexecutor = new HttpRequestExecutor();

        HttpCoreContext coreContext = HttpCoreContext.create();
        HttpHost host = new HttpHost("localhost", 8080);
        coreContext.setTargetHost(host);

        Out os = new Out("TestOut.txt");

        DefaultBHttpClientConnection conn = new DefaultBHttpClientConnection(8 * 1024);
        ConnectionReuseStrategy connStrategy = DefaultConnectionReuseStrategy.INSTANCE;

        try 
        {

            String[] targets = 
            {
                "http://www.google.com/"
            };

            for (int i = 0; i < targets.length; i++) 
            {
                if (!conn.isOpen()) 
                {
                    Socket socket = new Socket(host.getHostName(), host.getPort());
                    conn.bind(socket);
                }
                BasicHttpRequest request = new BasicHttpRequest("GET", targets[i]);
                os.println(">> Request URI: " + request.getRequestLine().getUri());

                httpexecutor.preProcess(request, httpproc, coreContext);
                HttpResponse response = httpexecutor.execute(request, conn, coreContext);
                httpexecutor.postProcess(response, httpproc, coreContext);

                os.println("<< Response: " + response.getStatusLine());
                os.println(EntityUtils.toString(response.getEntity()));
                os.println("==============");

                if (!connStrategy.keepAlive(response, coreContext)) 
                {
                    conn.close();
                }
                else 
                {
                    os.println("Connection kept alive...");
                }
            }
        }
        catch (IndexOutOfBoundsException iob)
        {
            os.println("What happened here?");
        }
        finally
        {
            conn.close();
        }

        return;
    }
}

Answer 1

...它们没有正常运行，给出“java.net.ConnectException”

这可能是由很多事情造成的。异常消息中有一些线索...您选择不与我们分享。

...“找不到或无法加载主类”

再次有多种可能的原因，并且异常消息中有线索......您选择不与我们分享。

但是您创建了一个 JAR 文件以及您提供的错误消息片段中的“Main-Class”提示这一事实表明您在创建 JAR 文件时犯了一个错误；即您为“Main-Class”属性使用了错误的名称。

鉴于该源代码，“Main-Class”属性应为“NewProject.NewProject”。我怀疑您将其设置为其他内容。

第二种可能是您没有正确处理对 Apache 库的依赖。 Apache 类需要位于 JAR 文件指定的类路径上。 （使用java -jar 启动时，不能使用-cp 参数或$CLASSPATH。）

---

我是白痴还是 Apache 库有点过时/不适合 Win 8/其他？

Apache 库没有任何问题。

Answer 2

您发布的代码似乎有点低级（例如，直接与 Socket 连接交互）。下面发布的代码应该为您提供您正在寻找的内容。使用的类还为您提供了很多设置和获取 http 参数（例如标头、超时等）的方法。

package org.yaorma.example.http.client;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpClientExample {

    public static void main(String[] args) throws Exception {
        String response;
        response = get("http://www.google.com");
        System.out.println("RESPONSE FROM GET -----------------------------------------");
        System.out.println(response);
        response = post("http://httpbin.org/post", "This is the message I posted to httpbin.org/post");
        System.out.println("RESPONSE FROM POST -----------------------------------------");
        System.out.println(response);
    }

    /**
     * Method to post a request to a given URL.
     */
    public static String post(String urlString, String message) {
        try {
            // get a connection
            URL url = new URL(urlString);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            // set the parameters
            conn.setRequestMethod("POST");
            conn.setDoOutput(true);
            // send the message
            OutputStream os = conn.getOutputStream();
            BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(os, "UTF-8"));
            writer.write(message);
            writer.flush();
            writer.close();
            os.close();
            // get the response
            conn.connect();
            InputStream content = (InputStream) conn.getInputStream();
            // read the response
            BufferedReader in = new BufferedReader(new InputStreamReader(content));
            String rtn = "";
            String line;
            while ((line = in.readLine()) != null) {
                rtn += line + "\n";
            }
            return rtn;
        } catch (Exception exp) {
            throw new RuntimeException(exp);
        }
    }

    /**
     * Method to do a get from a given URL.
     */
    public static String get(String urlString) {
        try {
            // get a connection
            URL url = new URL(urlString);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            // set the parameters
            conn.setRequestMethod("GET");
            conn.setDoOutput(true);
            // get the response
            conn.connect();
            InputStream content = (InputStream) conn.getInputStream();
            // read the response
            BufferedReader in = new BufferedReader(new InputStreamReader(content));
            String rtn = "";
            String line;
            while ((line = in.readLine()) != null) {
                rtn += line + "\n";
            }
            return rtn;
        } catch (Exception exp) {
            throw new RuntimeException(exp);
        }
    }

}