Question

我用Java实现了一个简单的基于插件的应用程序。主插件类派生自名为“Plugin”的抽象类。应用程序从JAR文件中读取该类，并通过创建该类的实例来运行该插件。标准程序我猜：）

到目前为止，一切都很好。但是当我将一个库包含到我的插件中时会出现问题，例如MySQL Connector。执行后抛出异常NoClassDefFoundError和ClassNotFoundException。我通过将MySQL连接器库添加到主应用程序来克服这个问题，但那又有什么意义呢？：）

我不是Java专家，所以我不确定是否有任何替代解决方案，例如为库等定义类路径。

这是我的插件加载器： http://pastebin.com/90rQ9NfJ

这是我的插件基类： http://pastebin.com/Juuicwkm

我正在从GUI执行：

    private void jButtonAddActionPerformed(java.awt.event.ActionEvent evt) {
        JFileChooser fileChooser = new JFileChooser();
        fileChooser.setFileFilter(new FileNameExtensionFilter("JTask Plugin (*.JAR)", "JAR"));

        if (fileChooser.showOpenDialog(this) == JFileChooser.APPROVE_OPTION)
        {
            File pluginFile = fileChooser.getSelectedFile();
            PluginLoader pluginLoader = new PluginLoader();
            Plugin plugin = pluginLoader.loadPlugin(pluginFile);
            if (plugin != null)
                jPanelPlugins.add(new PluginControl(jPanelPlugins, plugin));
        }
    }

Answer 1

您也应该包含您的源代码。

您是如何通过命令行或GUI执行该类的？如果从命令行，则必须在类路径（java -classpath）中包含MySQLConnector库以及任何其他依赖库。这个问题的最佳答案可以帮助您 - Java: how to import a jar file from command line

Answer 2

如果是这种情况，你的类是一个Mysql驱动程序，你必须排除（在类调用时）不可用的类。在.jar文件的文件夹中有一个名为“integration”的文件夹，它包含“jboss”和“c3p0”，目前不存在。

while (en.hasMoreElements()) { 
                JarEntry entry = new JarEntry(en.nextElement());
                String name = entry.getName();
                if (name.contains("/integration/")) {
                  continue;
                } else {
                 if (!entry.isDirectory() && name.toLowerCase().endsWith(".class"))
                 {
                    classList.add(name.replace(".class", ""));
                 }
                }
}

这应该加载一个mysql.xxx.jar文件。试试这个

<强> dynamicload.java

package dynamicloading;

import java.io.File;
import java.net.URL;
import java.net.URLClassLoader;
import java.sql.Connection;
import java.sql.Statement;
import java.sql.Driver;
import java.sql.DriverManager;
import java.sql.DriverPropertyInfo;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Enumeration;
import java.util.Properties;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

/**
 *
 * @author Administrator
 */
class com_mysql_jdbc_Driver implements Driver {
    private Driver driver;
    com_mysql_jdbc_Driver(Driver cmjd) {
        this.driver = cmjd;
    }
    @Override
    public boolean acceptsURL(String aurlS) throws SQLException {
        return this.driver.acceptsURL(aurlS);
    }
    @Override
    public Connection connect(String aurlS, Properties pP) throws SQLException {
        return this.driver.connect(aurlS, pP);
    }
    @Override
    public int getMajorVersion() {
        return this.driver.getMajorVersion();
    }
    @Override
    public int getMinorVersion() {
        return this.driver.getMinorVersion();
    }
    @Override
    public DriverPropertyInfo[] getPropertyInfo(String aurlS, Properties pP) throws SQLException {
        return this.driver.getPropertyInfo(aurlS, pP);
    }
    @Override
    public boolean jdbcCompliant() {
        return this.driver.jdbcCompliant();
    }
}

public class DynMain {

    /**
     * @param args the command line arguments
     */

    public static void main(String[] args) throws Exception {
        /* please set to your path*/
        File file = new File("U:/mozsamples/mysql-connector-java-5.1.19-bin.jar");
        Driver cmjdD;
        String aktCS;
        String urlS = "jdbc:mysql://localhost/db";
        String userS = "must-be-set";
        String passS = "must-be-set";
        Connection con;
        Statement stmt;
        URLClassLoader clazzLoader = URLClassLoader.newInstance(new URL[]{file.toURI().toURL()});
        JarFile jarFile = new JarFile(file);
        Enumeration<JarEntry> entries = jarFile.entries();

        while (entries.hasMoreElements()) {
            JarEntry element = entries.nextElement();
            if (element.getName().endsWith(".class")) {
                String name = element.getName();
                if (name.contains("/integration/")) {
                  System.out.println( "ignored: " + name );
                  continue;
                } else
                {
                try {    
                    aktCS = element.getName().replaceAll(".class", "").replaceAll("/", ".");
                    clazzLoader.loadClass(aktCS);
                    if (name.contains("com/mysql/jdbc/Driver")) {
                        cmjdD = (Driver)Class.forName(aktCS, true, clazzLoader).newInstance();
                        try {
                        DriverManager.registerDriver(new com_mysql_jdbc_Driver(cmjdD));
                        System.out.println( "register Class: " + aktCS );
                        } catch (SQLException e) {
                          e.printStackTrace();
                        }
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                }
                }
            }
        } 
    try {
    con = DriverManager.getConnection(urlS,userS,passS);
    stmt = con.createStatement();
    /*ResultSet rs = stmt.executeQuery("select * from idcart where ID=255"); */

    stmt.close();
    } catch (SQLException esql) {
        esql.printStackTrace();
    }
   int j=0 ;
   System.out.println("loaded Driver----------------------------------");
   for( Enumeration en = DriverManager.getDrivers() ; en.hasMoreElements() ; j++)
         System.out.println( en.nextElement().getClass().getName() );

   if (j==0) { System.out.println("Driverlist empty"); }

    System.out.println("-----------------------------------------------");
    }
}

<强>输出：

register Class: com.mysql.jdbc.Driver
ignored: com/mysql/jdbc/integration/c3p0/MysqlConnectionTester.class
ignored: com/mysql/jdbc/integration/jboss/ExtendedMysqlExceptionSorter.class
ignored: com/mysql/jdbc/integration/jboss/MysqlValidConnectionChecker.class
loaded Driver----------------------------------
sun.jdbc.odbc.JdbcOdbcDriver
dynamicloading.com_mysql_jdbc_Driver
-----------------------------------------------

好的???

URLClassLoader不读取插件的外部JAR库

2 个答案: