log4j ：一个完整的例子

import org.apache.log4j.or.ObjectRenderer;
import org.apache.log4j.Logger;

import org.apache.log4j.spi.Filter;
import org.apache.log4j.spi.LoggingEvent;

class CustomerOrder {

/** Holds value of property productName. */
private String productName;

/** Holds value of property productCode. */
private int productCode;

/** Holds value of property productPrice. */
private int productPrice;

/** Creates a new instance of CustomerOrder */
public CustomerOrder() {
}

public CustomerOrder(String name, int code, int price) {
this.productCode = code;
this.productPrice = price;
this.productName = name;
}

/**
* Getter for property productName.
*
* @return Value of property productName.
*/
public String getProductName() {
return this.productName;
}

/**
* Setter for property productName.
*
* @param productName
* New value of property productName.
*/
public void setProductName(String productName) {
this.productName = productName;
}

/**
* Getter for property productCode.
*
* @return Value of property productCode.
*/
public int getProductCode() {
return this.productCode;
}

/**
* Setter for property productCode.
*
* @param productCode
* New value of property productCode.
*/
public void setProductCode(int productCode) {
this.productCode = productCode;
}

/**
* Getter for property productPrice.
*
* @return Value of property productPrice.
*/
public int getProductPrice() {
return this.productPrice;
}

/**
* Setter for property productPrice.
*
* @param productPrice
* New value of property productPrice.
*/
public void setProductPrice(int productPrice) {
this.productPrice = productPrice;
}
}

class ProductFilter extends Filter {
/** Creates a new instance of ProductFilter */
public ProductFilter() {
}

public int decide(LoggingEvent event) {
int result = this.ACCEPT;
//obtaining the message object passed through Logger
Object message = event.getMessage();
//checking if the message object is of correct type
if (message instanceof CustomerOrder) {
CustomerOrder order = (CustomerOrder) message;
int productCode = order.getProductCode();
//checking for the product code greater than 100 only
if (productCode < 100) {
result = this.DENY;
}
} else {
//this filter can ignore this, pass to next filter
result = this.NEUTRAL;
}

return result;
}
}

class OrderRenderer implements ObjectRenderer {
private static final String separator = "-";

/** Creates a new instance of OrderRenderer */
public OrderRenderer() {
}

public String doRender(Object obj) {
StringBuffer buffer = new StringBuffer(50);
CustomerOrder order = null;
String productName = null;
int productCode = 0;
int productPrice = 0;
//check if the instance is of correct type CustomerOrder
if (obj instanceof CustomerOrder) {
order = (CustomerOrder) obj;
productName = order.getProductName();
productCode = order.getProductCode();
productPrice = order.getProductPrice();

buffer.append(productName);
buffer.append(separator);
buffer.append(new Integer(productCode).toString());
buffer.append(separator);
buffer.append(new Integer(productPrice).toString());
}

return buffer.toString();
}
}

public class ProductFilterDemo {
private static Logger logger = Logger.getLogger("name");

/** Creates a new instance of ProductFilterDemo */
public ProductFilterDemo() {
}

public void processOrder(CustomerOrder order) {
logger.info(order);
}

public static void main(String args[]) {
CustomerOrder order1 = new CustomerOrder("Beer", 101, 20);
CustomerOrder order2 = new CustomerOrder("Lemonade", 95, 10);
CustomerOrder order3 = new CustomerOrder("Chocolate", 223, 5);

ProductFilterDemo demo = new ProductFilterDemo();
demo.processOrder(order1);
demo.processOrder(order2);
demo.processOrder(order3);
}
}
//filter_properties.xml
/*
*
* <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE log4j:configuration SYSTEM
* "log4j.dtd">
*
* <log4j:configuration xmlns:log4j="http://jakarta.apache.org/log4j/">
*
* <renderer renderedClass="com.apress.business.CustomerOrder"
* renderingClass="com.apress.logging.log4j.renderer.OrderRenderer"> </renderer>
*
* <appender name="A1" class="org.apache.log4j.ConsoleAppender">
*
* <layout class="org.apache.log4j.PatternLayout"> <param
* name="ConversionPattern" value="%t %-5p %c{2} - %m%n"/> </layout> <filter
* class="com.apress.logging.log4j.filter.ProductFilter"/> </appender>
*
* <logger name="com.apress.logging.log4j"> <level value="debug"/> <appender-ref
* ref="A1"/> </logger> </log4j:configuration>
*/