使用外部 Jar 时出现 Eclipse Juno EE NoClassDefFoundError [英] Eclipse Juno EE NoClassDefFoundError when using external Jar

问题描述

我通过文件夹 -> 属性 -> 构建路径 -> 库 -> 添加外部 jar 在我的 eclipse 动态 web 项目中添加了一个外部 jar.

I added an external jar in my eclipse dynamic webproject via Folder -> properties -> build path -> Libraries -> add external jar.

代码在编译时运行良好.

The code is working fine on compile time.

package servlet;
import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletException;
import javax.servlet.annotation.MultipartConfig;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.apache.tika.Tika;

@WebServlet(name="UploadServlet", urlPatterns={"/uploadFile"})     // specify urlPattern for servlet
@MultipartConfig                       //Specify that this servlet will receive a multipart data
public class UploadServlet extends HttpServlet {

    protected void doPost(HttpServletRequest req, HttpServletResponse res) throws IOException, ServletException{
        Tika tika = new Tika();

        res.setContentType("text/html");
        PrintWriter writer = res.getWriter();
        writer.write(mediaType);
    }
}

我添加了 Apache Tika，但是当我运行我的应用程序时.发生了这些异常.

I added Apache Tika but when I run my application. these exception occured.

root cause 

java.lang.NoClassDefFoundError: org/apache/tika/Tika
    servlet.UploadServlet.doPost(UploadServlet.java:19)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)


root cause 

java.lang.ClassNotFoundException: org.apache.tika.Tika
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1714)
    org.apache.catalina.loader.WebappClassLoader.loadClass(WebappClassLoader.java:1559)
    servlet.UploadServlet.doPost(UploadServlet.java:19)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:641)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)

我正在使用 Apache Tika 来确定已上传的文件，我想用它来验证文件是图像还是音频文件

I am using Apache Tika to determine what file has been upload, I want to use it for validating if a file is an image, or audio file

推荐答案

您忘记将该 jar 添加到部署程序集页面.当您运行应用程序时，它不会部署到服务器，因此会出现 NoClassDefFoundErrors.

You forgot to add that jar to the Deployment Assembly page. It's not deployed to the server when you run your application, hence the NoClassDefFoundErrors.

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