org.finra.herd.dao

Class Log4jOverridableConfigurer

java.lang.Object

org.finra.herd.dao.Log4jOverridableConfigurer

All Implemented Interfaces:

org.springframework.beans.factory.Aware, org.springframework.beans.factory.config.BeanPostProcessor, org.springframework.context.ApplicationContextAware, org.springframework.core.Ordered, org.springframework.core.PriorityOrdered

public class Log4jOverridableConfigurer
extends Object
implements org.springframework.beans.factory.config.BeanPostProcessor, org.springframework.core.PriorityOrdered, org.springframework.context.ApplicationContextAware

Configure Log4J based on a possible resource override location, a possible database override location, and a default resource location, in that order. The Log4J configuration itself can include an optional "monitorInterval" attribute that allows the Log4J configuration to be monitored for changes and re-initialized if changes are found.

This class will write to System.out and System.err for output before the logging is successfully initialized. Once the logging is initialized, logging will go to where the logger is configured. Note that it is important to use valid Log4J configuration files for Log4J to work properly. If an invalid configuration file is used, Log4J will output the error to System.err, but will not throw an exception so this class will not know that logging hasn't been configured properly. That means that application logging messages could be lost. If logging was initialized successfully and a new override file is found that is invalid, the previous valid configuration will remain in effect until a new valid configuration is found.

This class contains nested named inner-classes. The reason for this was to keep everything required for the Log4JOverridableConfigurer functionality fully encapsulated within one file so it could be easily ported if needed.

This bean is a bean post processor and is priority ordered. By being a bean post processor, this class will get called early in the bean creation lifecycle: specifically after the beans are instantiated, but before they are used. By being priority ordered (as opposed to standard ordering), our bean will get called before other post processors. This is important to ensure logging is initialized before other things are initialized that could have problems. If other beans have problems and perform error logging (e.g. Hibernate session manager, Ehcache, JGroups), we will loose that logging if we haven't initialized our logging first.

To use a Log4J configuration specified in the database, configure these properties:

     dataSource: the data source for the database to connect to.
     tableName: the table name that contains the Log4J configuration.
     selectColumn: the column to select that contains the Log4J configuration.
     whereColumn and whereValue: an optional column name and value to filter on if multiple rows would be returned where a single row is required.
 

To use an externally specified Log4J override configuration, configure the overrideResourceLocation (e.g. file:///tmp/myOverride.xml).

To use the default Log4J configuration, specify an internally bundled defaultResourceLocation (e.g. classpath:herd-log4j.xml).

Given the difficulty of initializing Log4J from a non-URI such as the database, the approach taken is to read the configuration from the database and copy it to a temporary file on the file system and initializes Log4J from there. Then the database watchdog thread will re-read the configuration as specified in the configuration itself and will update the temporary file. Since the interval for the local file being updated and the interval when Log4J monitors the file for changes are different, the actual changes may be slightly delayed, but no longer than double the configured interval.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected class	Log4jOverridableConfigurer.JdbcOperation<T> An internally used helper class for simplifying database access through plain JDBC.
protected class	Log4jOverridableConfigurer.Log4jDbWatchdog An internally used watchdog thread that keeps querying the database to retrieve the Log4J configuration each time it wakes up.

Field Summary

Fields inherited from interface org.springframework.core.Ordered

HIGHEST_PRECEDENCE, LOWEST_PRECEDENCE

Constructor Summary

Constructors

Constructor and Description
Log4jOverridableConfigurer()

Method Summary

Modifier and Type	Method and Description
protected String	convertClob(Clob clob) Converts a CLOB to a string.
protected String	getConfigurationFromResultSet(ResultSet resultSet, String selectColumn) Extracts the configuration from the given result set.
protected String	getLog4JConfigurationFromDatabase() Gets the Log4J override configuration from the database.
int	getOrder()
Object	postProcessAfterInitialization(Object bean, String beanName)
Object	postProcessBeforeInitialization(Object bean, String beanName)
void	setApplicationContext(org.springframework.context.ApplicationContext applicationContext)
void	setDataSource(DataSource dataSource) Sets the data source to use when connecting to the database to get the Log4J override configuration.
void	setDefaultResourceLocation(String defaultResourceLocation) The default Log4J configuration location to use if the override location isn't found.
void	setOverrideResourceLocation(String overrideResourceLocation) Set the Log4J override configuration resource location to use.
void	setRefreshIntervalSeconds(int refreshIntervalSeconds) Sets the interval seconds for refreshing log4j configuration configuration.
void	setSelectColumn(String selectColumn) Sets the column to be selected (from the specified "tableName") that contains the Log4J database override configuration.
void	setTableName(String tableName) Sets the table name that contains the Log4J database override configuration.
void	setWhereColumn(String whereColumn) Sets the optional where column to filter on to determine which row to retrieve that contains the Log4J database override configuration.
void	setWhereValue(String whereValue) Sets the optional where clause value to filter on to determine which row to retrieve that contains the Log4J database override configuration.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Log4jOverridableConfigurer

public Log4jOverridableConfigurer()

Method Detail

postProcessBeforeInitialization

public Object postProcessBeforeInitialization(Object bean,
                                              String beanName)
                                       throws org.springframework.beans.BeansException

Specified by:

postProcessBeforeInitialization in interface org.springframework.beans.factory.config.BeanPostProcessor

Throws:

org.springframework.beans.BeansException

postProcessAfterInitialization

public Object postProcessAfterInitialization(Object bean,
                                             String beanName)
                                      throws org.springframework.beans.BeansException

Specified by:

postProcessAfterInitialization in interface org.springframework.beans.factory.config.BeanPostProcessor

Throws:

org.springframework.beans.BeansException

getLog4JConfigurationFromDatabase

protected String getLog4JConfigurationFromDatabase()

Gets the Log4J override configuration from the database.

Returns:

the Log4J configuration or null if no configuration was found.

getConfigurationFromResultSet

protected String getConfigurationFromResultSet(ResultSet resultSet,
                                               String selectColumn)
                                        throws SQLException

Extracts the configuration from the given result set. The passed in ResultSet was created by a SELECT statement on the underlying database table. The selectColumn is the column that will be retrieved from the result set. Normally the contained value is directly returned. However, if it is of type CLOB, text is extracted as string. This method was mostly obtained from the DatabaseConfiguration class.

Parameters:

resultSet - the current ResultSet

selectColumn - the selected column to obtain from the result set.

Returns:

the Log4J configuration.

Throws:

SQLException - if an error occurs.

convertClob

protected String convertClob(Clob clob)
                      throws SQLException

Converts a CLOB to a string. This method was mostly obtained from DatabaseConfiguration.

Parameters:

clob - the CLOB to be converted.

Returns:

the extracted string value.

Throws:

SQLException - if an error occurs.

getOrder

public int getOrder()

Specified by:

getOrder in interface org.springframework.core.Ordered

setApplicationContext

public void setApplicationContext(org.springframework.context.ApplicationContext applicationContext)
                           throws org.springframework.beans.BeansException

Specified by:

setApplicationContext in interface org.springframework.context.ApplicationContextAware

Throws:

org.springframework.beans.BeansException

setOverrideResourceLocation

public void setOverrideResourceLocation(String overrideResourceLocation)

Set the Log4J override configuration resource location to use. If the override location doesn't exist, the default resource location will be attempted.

Parameters:

overrideResourceLocation - the location.

setDefaultResourceLocation

public void setDefaultResourceLocation(String defaultResourceLocation)

The default Log4J configuration location to use if the override location isn't found.

Parameters:

defaultResourceLocation - the default location.

setTableName

public void setTableName(String tableName)

Sets the table name that contains the Log4J database override configuration.

Parameters:

tableName - the table name.

setSelectColumn

public void setSelectColumn(String selectColumn)

Sets the column to be selected (from the specified "tableName") that contains the Log4J database override configuration.

Parameters:

selectColumn - the select column.

setWhereColumn

public void setWhereColumn(String whereColumn)

Sets the optional where column to filter on to determine which row to retrieve that contains the Log4J database override configuration. If no where column or value is specified, then only one row should exist in the specified table.

Parameters:

whereColumn - the where column to filter on.

setWhereValue

public void setWhereValue(String whereValue)

Sets the optional where clause value to filter on to determine which row to retrieve that contains the Log4J database override configuration. If no where column or value is specified, then only one row should exist in the specified table.

Parameters:

whereValue - the where value to filter on.

setDataSource

public void setDataSource(DataSource dataSource)

Sets the data source to use when connecting to the database to get the Log4J override configuration.

Parameters:

dataSource - the data source.

setRefreshIntervalSeconds

public void setRefreshIntervalSeconds(int refreshIntervalSeconds)

Sets the interval seconds for refreshing log4j configuration configuration.

Parameters:

refreshIntervalSeconds - the refresh interval seconds.