javax.servlet.ServletException: java.lang.NoClassD

问题:

I'm trying to establish a connection to an Oracle database using BasicDataSource using DBCP.

I downloaded commons-dbcp-1.4-bin.zip from here.

There are three jar files on the classpath.

1. commons-dbcp-1.4
2. commons-dbcp-1.4-sources
3. commons-dbcp-1.4-javadoc

I'm using the following code for the connection to be established.

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import org.apache.commons.dbcp.BasicDataSource;

public class DatabaseConnection {

    private final static BasicDataSource BASIC_DATA_SOURCE = new BasicDataSource();
    private final static String SQL = "SELECT * FROM admin WHERE login_id=? AND admin_pwd=?";

    static {
        BASIC_DATA_SOURCE.setDriverClassName("oracle.jdbc.OracleDriver");
        BASIC_DATA_SOURCE.setUrl("jdbc:oracle:thin:@localhost:1521:xe");
        BASIC_DATA_SOURCE.setUsername("wagafashiondb");
        BASIC_DATA_SOURCE.setPassword("root");
    }

    private static Connection getConnection() throws SQLException {
        return BASIC_DATA_SOURCE.getConnection();
    }

    public boolean exists(String userName, String password) throws SQLException {
        Connection connection = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        boolean exists = false;

        try {
            connection = getConnection();
            ps = connection.prepareStatement(SQL);
            ps.setString(1, userName);
            ps.setString(2, password);
            rs = ps.executeQuery();
            exists = rs.next();
        } finally {
            try {
                if (connection != null) {connection.close();}
                if (ps != null) {ps.close();}
                if (rs != null) {rs.close();}
            } catch (SQLException e) {

            }
        }
        return exists;
    }
}

It throws the following exception,

javax.servlet.ServletException: java.lang.NoClassDefFoundError: org/apache/commons/pool/KeyedObjectPoolFactory

It appears to imply that I'm using a wrong source. What might be the reason for this exception to be caused?

回答1:

Solution

You need to get the commons-pool library (JAR) on a classpath. The fact is indicated as commons-pool being a dependency of commons-dbcp in project's dependecies list

Explanation

Basically the NoClassDefFoundError means the Java execution turned out to require a specific class which is not on classpath. This is because classes needs other classes (typically indicated in imports). In your case (at least) one of the classes from commons-dbcp declares a dependency to org/apache/commons/pool/KeyedObjectPoolFactory.

The name of the class is given using / as separators. If that's a common name (not your own class), you may try to find where to get it from by just typing the full name (e.g. org/apache/commons/pool/KeyedObjectPoolFactory) in Google.