让Log4j支持数据源--国外高手的封装

package nl.iprofs.blogs.log4j.databaselogging;
 
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import javax.naming.Context;
import javax.naming.InitialContext;
import javax.naming.NamingException;
import javax.sql.DataSource;
import org.apache.log4j.jdbc.JDBCAppender;
import org.apache.log4j.spi.ErrorCode;
 
/**
 * Extension of the log4j {@link JDBCAppender} to allow using a JNDI data source
 * rather than a direct connection.
 *
 * <p>
 * Example configuration:
 * <pre>
 *   <appender name="database" class="nl.iprofs.blogs.log4j.databaselogging.JndiCapableJdbcAppender">
 *     <param name="jndiDataSource" value="java:comp/jdbc/datasource" />
 *     <layout class="org.apache.log4j.PatternLayout">
 *       <param name="ConversionPattern" value="INSERT INTO logging (timestamp, level, location, message) VALUES ('%d{yyyy-MM-dd HH:mm:ss.sss}','%p','%c{1}','%m')" />
 *     </layout>
 *   </appender>
 * </pre>
 *
 * @author Bart Bakker
 */
public class JndiCapableJdbcAppender extends JDBCAppender {
 
    private static final Pattern SQL_VALUE_PATTERN = Pattern.compile("'(.*?)'(?=\\s*[,)])", Pattern.MULTILINE);
    private String jndiDataSource;
 
    /** {@inheritDoc} */
    @Override
    protected Connection getConnection() throws SQLException {
        if (jndiDataSource == null) {
            return super.getConnection();
        } else {
            return lookupDataSource().getConnection();
        }
    }
 
    /**
     * Looks up the datasource in the naming context specified by the
     * {@link #jndiDataSource}.
     *
     * @return the datasource.
     */
    private DataSource lookupDataSource() {
        try {
            Context context = new InitialContext();
            return (DataSource) context.lookup(jndiDataSource);
        } catch (NamingException e) {
            throw new RuntimeException("Cannot find JNDI DataSource: " + jndiDataSource, e);
        }
    }
 
    /** {@inheritDoc} */
    @Override
    protected void closeConnection(Connection con) {
        try {
            con.close();
        } catch (SQLException e) {
            errorHandler.error("Failed to close connection", e, ErrorCode.CLOSE_FAILURE);
        }
    }
 
    /**
     * Executes the specified SQL statement, by parsing its values and turning
     * them into parameters, so that characters that must be escaped in a SQL
     * statement are supported.
     */
    @Override
    protected void execute(String sql) throws SQLException {
        String statement = sql;
        ArrayList<String> args = new ArrayList<String>();
        Matcher m = SQL_VALUE_PATTERN.matcher(sql);
        while (m.find()) {
            args.add(m.group(1));
            statement = statement.replace(m.group(), "?");
        }
 
        executeStatement(statement, args.toArray(new String[args.size()]));
    }
 
    /**
     * Executes the statement settings its parameters to the specified arguments.
     * 
     * @param statement
     *            the statement to execute.
     * @param args
     *            the parameter values.
     */
    protected void executeStatement(String statement, String[] args) throws SQLException {
        Connection con = getConnection();
        PreparedStatement stmt = null;
        try {
            stmt = con.prepareStatement(statement);
            for (int i = 0; i < args.length; i++) {
                stmt.setString(i + 1, args[i]);
            }
            stmt.executeUpdate();
        } catch (SQLException e) {
            if (stmt != null) {
                stmt.close();
            }
            throw e;
        }
        stmt.close();
        closeConnection(con);
    }
 
    public String getJndiDataSource() {
        return jndiDataSource;
    }
 
    public void setJndiDataSource(String jndiDataSource) {
        this.jndiDataSource = jndiDataSource;
    }
}