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本文主要研究一下logback的EvaluatorFilter
EvaluatorFilter
ch/qos/logback/core/filter/EvaluatorFilter.java
代码语言：javascript复制public class EvaluatorFilter<E> extends AbstractMatcherFilter<E> {
EventEvaluator<E> evaluator;
@Override
public void start() {
if (evaluator != null) {
super.start();
} else {
addError("No evaluator set for filter " this.getName());
}
}
public EventEvaluator<E> getEvaluator() {
return evaluator;
}
public void setEvaluator(EventEvaluator<E> evaluator) {
this.evaluator = evaluator;
}
public FilterReply decide(E event) {
// let us not throw an exception
// see also bug #17.
if (!isStarted() || !evaluator.isStarted()) {
return FilterReply.NEUTRAL;
}
try {
if (evaluator.evaluate(event)) {
return onMatch;
} else {
return onMismatch;
}
} catch (EvaluationException e) {
addError("Evaluator " evaluator.getName() " threw an exception", e);
return FilterReply.NEUTRAL;
}
}
}EvaluatorFilter继承了AbstractMatcherFilter，其decide方法在evaluator.evaluate(event)为true时返回onMatch，否则返回onMismatch，异常的话返回NEUTRAL
EventEvaluator
ch/qos/logback/core/boolex/EventEvaluator.java
代码语言：javascript复制public interface EventEvaluator<E> extends ContextAware, LifeCycle {
/**
* Evaluates whether the event passed as parameter matches some user-specified
* criteria.
*
* <p>
* The <code>Evaluator</code> is free to evaluate the event as it pleases. In
* particular, the evaluation results <em>may</em> depend on previous events.
*
* @param event The event to evaluate
* @return true if there is a match, false otherwise.
* @throws NullPointerException can be thrown in presence of null values
* @throws EvaluationException may be thrown during faulty evaluation
*/
boolean evaluate(E event) throws NullPointerException, EvaluationException;
/**
* Evaluators are named entities.
*
* @return The name of this evaluator.
*/
String getName();
/**
* Evaluators are named entities.
*/
void setName(String name);
}EventEvaluator接口定义了evaluate、getName、setName方法
EventEvaluatorBase
ch/qos/logback/core/boolex/EventEvaluatorBase.java
代码语言：javascript复制abstract public class EventEvaluatorBase<E> extends ContextAwareBase implements EventEvaluator<E> {
String name;
boolean started;
public String getName() {
return name;
}
public void setName(String name) {
if (this.name != null) {
throw new IllegalStateException("name has been already set");
}
this.name = name;
}
public boolean isStarted() {
return started;
}
public void start() {
started = true;
}
public void stop() {
started = false;
}
}EventEvaluatorBase声明实现EventEvaluator，它主要是定义了name、started属性，另外还有一个抽象子类为EventEvaluatorBase，而JaninoEventEvaluatorBase抽象子类继承了EventEvaluatorBase，它们有基于IAccessEvent，也有基于ILoggingEvent。
OnMarkerEvaluator
ch/qos/logback/classic/boolex/OnMarkerEvaluator.java
代码语言：javascript复制public class OnMarkerEvaluator extends EventEvaluatorBase<ILoggingEvent> {
List<String> markerList = new ArrayList<String>();
public void addMarker(String markerStr) {
markerList.add(markerStr);
}
/**
* Return true if event passed as parameter contains one of the specified
* user-markers.
*/
public boolean evaluate(ILoggingEvent event) throws NullPointerException, EvaluationException {
List<Marker> markerListInEvent = event.getMarkerList();
if (markerListInEvent == null || markerListInEvent.isEmpty()) {
return false;
}
for (String markerStr : markerList) {
for (Marker markerInEvent : markerListInEvent) {
if (markerInEvent.contains(markerStr)) {
return true;
}
}
}
return false;
}
}OnMarkerEvaluator继承了EventEvaluatorBase，其evaluate从ILoggingEvent获取markerListInEvent，然后判断markerListInEvent是否有包含指定的markerStr
OnErrorEvaluator
ch/qos/logback/classic/boolex/OnErrorEvaluator.java
代码语言：javascript复制public class OnErrorEvaluator extends EventEvaluatorBase<ILoggingEvent> {
/**
* Return true if event passed as parameter has level ERROR or higher, returns
* false otherwise.
*/
public boolean evaluate(ILoggingEvent event) throws NullPointerException, EvaluationException {
return event.getLevel().levelInt >= Level.ERROR_INT;
}
}OnErrorEvaluator继承了EventEvaluatorBase，其evaluate方法根据event的level来判断看是否大于等于ERROR级别
JaninoEventEvaluatorBase
ch/qos/logback/core/boolex/JaninoEventEvaluatorBase.java
代码语言：javascript复制abstract public class JaninoEventEvaluatorBase<E> extends EventEvaluatorBase<E> {
static Class<?> EXPRESSION_TYPE = boolean.class;
static Class<?>[] THROWN_EXCEPTIONS = new Class[1];
static public final int ERROR_THRESHOLD = 4;
static {
THROWN_EXCEPTIONS[0] = EvaluationException.class;
}
private String expression;
ScriptEvaluator scriptEvaluator;
private int errorCount = 0;
public void start() {
try {
assert context != null;
scriptEvaluator = new ScriptEvaluator(getDecoratedExpression(), EXPRESSION_TYPE, getParameterNames(),
getParameterTypes(), THROWN_EXCEPTIONS);
super.start();
} catch (Exception e) {
addError("Could not start evaluator with expression [" expression "]", e);
}
}
public boolean evaluate(E event) throws EvaluationException {
if (!isStarted()) {
throw new IllegalStateException("Evaluator [" name "] was called in stopped state");
}
try {
Boolean result = (Boolean) scriptEvaluator.evaluate(getParameterValues(event));
return result;
} catch (Exception ex) {
errorCount ;
if (errorCount >= ERROR_THRESHOLD) {
stop();
}
throw new EvaluationException("Evaluator [" name "] caused an exception", ex);
}
}
//......
} JaninoEventEvaluatorBase在start的时候先通过getDecoratedExpression获取修饰之后的表达式，然后创建ScriptEvaluator，evaluate方法则通过getParameterValues从event提取参数，然后通过scriptEvaluator.evaluate获取结果
示例
代码语言：javascript复制 <filter class="ch.qos.logback.core.filter.EvaluatorFilter">
<evaluator class="ch.qos.logback.classic.boolex.OnMarkerEvaluator">
<marker>consoleOnly</marker>
</evaluator>
<onMatch>DENY</onMatch>
</filter>这里配置了EvaluatorFilter，其evaluator为OnMarkerEvaluator，包含consoleOnly这个marker时返回true，命中返回DENY
小结
logback的EvaluatorFilter继承了AbstractMatcherFilter，其decide方法在evaluator.evaluate(event)为true时返回onMatch，否则返回onMismatch，异常的话返回NEUTRAL。evaluator主要有OnMarkerEvaluator、OnErrorEvaluator以及JaninoEventEvaluatorBase系列的evaluator；JaninoEventEvaluatorBase它可以定义expression，通过ScriptEvaluator进行evaluate。
