给Log4j配上数据库连接池[1]

   我们都知道log4j是一个优秀的开源日志记录项目，我们不仅可以对输出的日志的格式自定义，还可以自己定义日志输出的目的地，比如：屏幕，文本文件，数据库，甚至能通过socket输出。
        现在让我们对日志输出到数据库来进行配置
         配置如下：
#---JDBC ---输出到数据库
# JDBCAppender log4j.properties file
#log4j.rootCategory=WARN,JDBC
# APPENDER JDBC
log4j.appender.JDBC=org.apache.log4j.jdbc.JDBCAppender
log4j.appender.JDBC.driver=com.mysql.jdbc.Driver
log4j.appender.JDBC.URL=jdbc:mysql://localhost:3306/test
log4j.appender.JDBC.user=use
log4j.appender.JDBC.password=password
log4j.appender.JDBC.layout=org.apache.log4j.PatternLayout
log4j.appender.JDBC.sql=INSERT INTO LOGGING (log_date, log_level, location, message) VALUES ('%d{ISO8601}', '%-5p', '%C,%L', '%m')

表结构如下：
log_date   varchar2(50)
log_level  varchar2(5)
location   varchar2(100) 
message    varchar2(1000)
笔者照做，但没有运行成功，而且此种方法是利用传统的数据库连接方法，对于数据库的管理和效率严重不足，在现在这个连接池横行的时代,为什么我们不能给给Log4j配上连接池，让Log4j利用数据连接池的连接和数据库进行通讯。现查看Log4j的Api,发现JDBCAppender这个类有以下几段话：WARNING: This version of JDBCAppender is very likely to be completely replaced in the future. Moreoever, it does not log exceptions. The JDBCAppender provides for sending log events to a database.

For use as a base class:

• Override getConnection() to pass any connection you want. Typically this is used to enable application wide connection pooling.
• Override closeConnection(Connection con) -- if you override getConnection make sure to implement closeConnection to handle the connection you generated. Typically this would return the connection to the pool it came from.
• Override getLogStatement(LoggingEvent event) to produce specialized or dynamic statements. The default uses the sql option value.

原来log4j建议我们把其提供的JDBCAppender作为基类来使用，然后Override三个父类的方法：getConnection(),closeConnection(Connection con)和getLogStatement(LoggingEvent event)。
原来如此，那就写一个子类JDBCPoolAppender来替代这个JDBCAppender
JDBCPoolAppender代码和其相关代码如下：

JDBCPoolAppender.java:

package common.log;
import java.sql.Connection;
import org.apache.log4j.spi.LoggingEvent;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Iterator;
import org.apache.log4j.spi.ErrorCode;
import org.apache.log4j.PatternLayout;
import common.sql.MyDB;
import common.sql.GeneralDb;

public class JDBCPoolAppender extends org.apache.log4j.jdbc.JDBCAppender {
   
    private MyDB mydb = null;  
    protected String sqlname=""; //增加一个数据库jndiName的属性
    protected Connection connection = null;
    protected String sqlStatement = "";
    /**
     * size of LoggingEvent buffer before writting to the database.
     * Default is 1.
     */
    protected int bufferSize = 1;

    public JDBCPoolAppender() {
        super();
    }

    /**
     * ArrayList holding the buffer of Logging Events.
     */
    public void append(LoggingEvent event) {
        buffer.add(event);
        if (buffer.size() >= bufferSize)
            flushBuffer();
    }

    /**
     * By default getLogStatement sends the event to the required Layout object.
     * The layout will format the given pattern into a workable SQL string.
     *
     * Overriding this provides direct access to the LoggingEvent
     * when constructing the logging statement.
     *
     */
    protected String getLogStatement(LoggingEvent event) {
        return getLayout().format(event);
    }