http://blog.csdn.net/socoolfj/article/details/542169 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

http://blog.csdn.net/socoolfj/article/details/542169

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:

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){
sqlname=sqlname;
}

public String getSqlname(){
return sqlname;
}

public void setBufferSize(int newBufferSize) {
bufferSize = newBufferSize;
buffer.ensureCapacity(bufferSize);
removes.ensureCapacity(bufferSize);
}

public int getBufferSize() {
return bufferSize;
}
}

MyDB.java:
package common.sql;
import java.sql.*;
import com.codestudio.sql.*; //引入开源项目Poolman数据库连接池的包

public class MyDB {
public static final String module = MyDB.class.getName();
private String dbName = "";
private PoolMan plmn = null;

public MyDB(String dbName) {
try {
if (plmn == null) {
plmn = (PoolMan) Class.forName("com.codestudio.sql.PoolMan").
newInstance();
}
} catch (Exception ec) {
System.out.println(ec.toString()+module);
}
this.dbName = dbName;
}

private Connection getNewConnection() {
Connection conn = null;
try {
conn = plmn.connect("jdbc:poolman://" + dbName);
conn.setAutoCommit(true);
} catch (Exception ec) {
System.out.println(ec.toString()+"First:Connect sqlsever failed"+module);
try {
Thread.sleep(1000);
conn = plmn.connect("jdbc:poolman://" + dbName);
conn.setAutoCommit(true);
} catch (Exception ecs) {
System.out.println(ecs.toString()+"Again:Connect sqlsever faile"+module);
}
}
return conn;
}

public Connection getConnection() {
return getNewConnection();
}
}
GeneralDb.java:

package common.sql;

import java.util.*;

public class GeneralDb {
private static Hashtable dbPool;
public static MyDB getInstance(String dbname) {
if (dbPool == null) {
dbPool = new Hashtable();
}
MyDB db = (MyDB) dbPool.get(dbname);
if (db == null) {
db = new MyDB(dbname);
dbPool.put(dbname, db);
}
return db;
}
}

Log4j数据库连接池的配置如下：
log4j.appender.JDBC=common.log.JDBCPoolAppender
log4j.appender.JDBC.sqlname=log
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')


poolman.xml配置如下：

〈?xml version="1.0" encoding="UTF-8"?>
〈poolman>
〈management-mode>local〈/management-mode>
〈datasource>
〈dbname>log〈/dbname>
〈jndiName>log〈/jndiName>
〈driver>com.mysql.jdbc.Driver〈/driver>
〈url>jdbc:mysql://localhost:3306/test〈/url>
〈username>use〈/username>
〈password>password〈/password>
〈minimumSize>0〈/minimumSize>
〈maximumSize>10〈/maximumSize>
〈logFile>logs/mysql.log〈/logFile>
〈/datasource>

〈/poolman>


运行成功！对于JDBCPoolAppender的属性（比如sqlname属性）我们可以利用Log4j的反射机制随便添加，只要在配置文件给其附上值即可应用，而原来的父类里面的一些属性（username什么的)和其get,set方法由于在连接池中不需要，所以删除。而在JDBCPoolAppender类中，我也只是将getConnection 方法Override ，在这个方法中我们可以根据需要生成我们的Connection对象，另外两个方法大家可以根据需求来决定怎样Override。：）