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_levelvarchar2(5)
location varchar2(100)
messagevarchar2(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);
}
/**
*
* Override this to provide an alertnate method of getting
* connections (such as caching).One method to fix this is to open
* connections at the start of flushBuffer() and close them at the
* end.I use a connection pool outside of JDBCAppender which is
* accessed in an override of this method.
* */
protected void execute(String sql) throws SQLException {
Connection con = null;
Statement stmt = null;
try {
con = getConnection();
stmt = con.createStatement();
stmt.executeUpdate(sql);
} catch (SQLException e) {
if (stmt != null)
stmt.close();
throw e;
}
stmt.close();
closeConnection(con);
//System.out.println("Execute: " + sql);
}
/**
* Override this to return the connection to a pool, or to clean up the
* resource.
*
* The default behavior holds a single connection open until the appender
* is closed (typically when garbage collected).
*/
protected void closeConnection(Connection con) {
mydb=null;
try {
if (connection != null && !connection.isClosed())
connection.close();
} catch (SQLException e) {
errorHandler.error("Error closing connection", e,
ErrorCode.GENERIC_FAILURE);
}
}
/**
* Override 此函数来利用连接池返回一个Connetion对象
*
*/
protected Connection getConnection() throws SQLException {
try {
mydb = GeneralDb.getInstance(sqlname);
connection = mydb.getConnection();
} catch (Exception e) {
errorHandler.error("Error opening connection", e, ErrorCode.GENERIC_FAILURE);
}
return connection;
}
/**
* Closes the appender, flushing the buffer first then closing the default
* connection if it is open.
*/
public void close() {
flushBuffer();
try {
if (connection != null && !connection.isClosed())
connection.close();
} catch (SQLException e) {
errorHandler.error("Error closing connection", e,
ErrorCode.GENERIC_FAILURE);
}
this.closed = true;
}
/**
* loops through the buffer of LoggingEvents, gets a
* sql string from getLogStatement() and sends it to execute().
* Errors are sent to the errorHandler.
*
* If a statement fails the LoggingEvent stays in the buffer!
*/
public void flushBuffer() {
//Do the actual logging
removes.ensureCapacity(buffer.size());
for (Iterator i = buffer.iterator(); i.hasNext(); ) {
try {
LoggingEvent logEvent = (LoggingEvent) i.next();
String sql = getLogStatement(logEvent);
execute(sql);
removes.add(logEvent);
} catch (SQLException e) {
errorHandler.error("Failed to excute sql", e,
ErrorCode.FLUSH_FAILURE);
}
}
// remove from the buffer any events that were reported
buffer.removeAll(removes);
// clear the buffer of reported events
removes.clear();
}
/** closes the appender before disposal */
public void finalize() {
close();
}
/**
* JDBCAppender requires a layout.
* */
public boolean requiresLayout() {
return true;
}
/**
*
*/
public void setSql(String s) {
sqlStatement = s;
if (getLayout() == null) {
this.setLayout(new PatternLayout(s));
} else {
((PatternLayout) getLayout()).setConversionPattern(s);
}
}
/**
* Returns pre-formated statement eg: insert into LogTable (msg) values ("%m")
*/
public String getSql() {
return sqlStatement;
}
public void setSqlname(String sqlname){
（出处：http://www.knowsky.com）
