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本文主要研究一下logback的ThrowableProxyConverter

ThrowableHandlingConverter

ch/qos/logback/classic/pattern/ThrowableHandlingConverter.java

/*** Converter which handle throwables should be derived from this class.**/
public abstract class ThrowableHandlingConverter extends ClassicConverter {boolean handlesThrowable() {return true;}
}

ThrowableHandlingConverter继承了ClassicConverter，其handlesThrowable方法返回true

ThrowableProxyConverter

ch/qos/logback/classic/pattern/ThrowableProxyConverter.java

public class ThrowableProxyConverter extends ThrowableHandlingConverter {protected static final int BUILDER_CAPACITY = 2048;int lengthOption;List<EventEvaluator<ILoggingEvent>> evaluatorList = null;List<String> ignoredStackTraceLines = null;int errorCount = 0;@SuppressWarnings("unchecked")public void start() {String lengthStr = getFirstOption();if (lengthStr == null) {lengthOption = Integer.MAX_VALUE;} else {lengthStr = lengthStr.toLowerCase();if ("full".equals(lengthStr)) {lengthOption = Integer.MAX_VALUE;} else if ("short".equals(lengthStr)) {lengthOption = 1;} else {try {lengthOption = Integer.parseInt(lengthStr);} catch (NumberFormatException nfe) {addError("Could not parse [" + lengthStr + "] as an integer");lengthOption = Integer.MAX_VALUE;}}}final List<String> optionList = getOptionList();if (optionList != null && optionList.size() > 1) {final int optionListSize = optionList.size();for (int i = 1; i < optionListSize; i++) {String evaluatorOrIgnoredStackTraceLine = (String) optionList.get(i);Context context = getContext();Map<String, EventEvaluator<?>> evaluatorMap = (Map<String, EventEvaluator<?>>) context.getObject(CoreConstants.EVALUATOR_MAP);EventEvaluator<ILoggingEvent> ee = (EventEvaluator<ILoggingEvent>) evaluatorMap.get(evaluatorOrIgnoredStackTraceLine);if (ee != null) {addEvaluator(ee);} else {addIgnoreStackTraceLine(evaluatorOrIgnoredStackTraceLine);}}}super.start();}//......
}    

ThrowableProxyConverter继承了ThrowableHandlingConverter，其start方法会先读取getFirstOption，该参数为lengthOption，为null则取Integer.MAX_VALUE，若为full则取Integer.MAX_VALUE，为short取1，其他的则解析该值，出现异常则取Integer.MAX_VALUE；之后取optionList的其他值，先通过evaluatorMap来取，若EventEvaluator不为null则执行addEvaluator，否则执行addIgnoreStackTraceLine

addEvaluator

    private void addEvaluator(EventEvaluator<ILoggingEvent> ee) {if (evaluatorList == null) {evaluatorList = new ArrayList<EventEvaluator<ILoggingEvent>>();}evaluatorList.add(ee);}

addEvaluator则是添加到evaluatorList

addIgnoreStackTraceLine

    private void addIgnoreStackTraceLine(String ignoredStackTraceLine) {if (ignoredStackTraceLines == null) {ignoredStackTraceLines = new ArrayList<String>();}ignoredStackTraceLines.add(ignoredStackTraceLine);}

addIgnoreStackTraceLine则是添加到ignoredStackTraceLines

convert

    public String convert(ILoggingEvent event) {IThrowableProxy tp = event.getThrowableProxy();if (tp == null) {return CoreConstants.EMPTY_STRING;}// an evaluator match will cause stack printing to be skippedif (evaluatorList != null) {boolean printStack = true;for (int i = 0; i < evaluatorList.size(); i++) {EventEvaluator<ILoggingEvent> ee = evaluatorList.get(i);try {if (ee.evaluate(event)) {printStack = false;break;}} catch (EvaluationException eex) {errorCount++;if (errorCount < CoreConstants.MAX_ERROR_COUNT) {addError("Exception thrown for evaluator named [" + ee.getName() + "]", eex);} else if (errorCount == CoreConstants.MAX_ERROR_COUNT) {ErrorStatus errorStatus = new ErrorStatus("Exception thrown for evaluator named [" + ee.getName() + "].", this, eex);errorStatus.add(new ErrorStatus("This was the last warning about this evaluator's errors."+ "We don't want the StatusManager to get flooded.", this));addStatus(errorStatus);}}}if (!printStack) {return CoreConstants.EMPTY_STRING;}}return throwableProxyToString(tp);}

convert方法先从event获取IThrowableProxy，若为null则返回空字符串；之后判断evaluatorList是否为null，不为null则遍历挨个执行evaluate(event)，若为true则printStack设置为false，跳出循环，当printStack为false时，返回空字符串，否则通过throwableProxyToString转为字符串返回

throwableProxyToString

    protected String throwableProxyToString(IThrowableProxy tp) {StringBuilder sb = new StringBuilder(BUILDER_CAPACITY);recursiveAppend(sb, null, ThrowableProxyUtil.REGULAR_EXCEPTION_INDENT, tp);return sb.toString();}private void recursiveAppend(StringBuilder sb, String prefix, int indent, IThrowableProxy tp) {if (tp == null)return;subjoinFirstLine(sb, prefix, indent, tp);sb.append(CoreConstants.LINE_SEPARATOR);subjoinSTEPArray(sb, indent, tp);IThrowableProxy[] suppressed = tp.getSuppressed();if (suppressed != null) {for (IThrowableProxy current : suppressed) {recursiveAppend(sb, CoreConstants.SUPPRESSED, indent + ThrowableProxyUtil.SUPPRESSED_EXCEPTION_INDENT, current);}}recursiveAppend(sb, CoreConstants.CAUSED_BY, indent, tp.getCause());}

throwableProxyToString主要是递归执行recursiveAppend，它先执行subjoinFirstLine、再执行subjoinSTEPArray、最后继续递归

subjoinSTEPArray

    protected void subjoinSTEPArray(StringBuilder buf, int indent, IThrowableProxy tp) {StackTraceElementProxy[] stepArray = tp.getStackTraceElementProxyArray();int commonFrames = tp.getCommonFrames();boolean unrestrictedPrinting = lengthOption > stepArray.length;int maxIndex = (unrestrictedPrinting) ? stepArray.length : lengthOption;if (commonFrames > 0 && unrestrictedPrinting) {maxIndex -= commonFrames;}int ignoredCount = 0;for (int i = 0; i < maxIndex; i++) {StackTraceElementProxy element = stepArray[i];if (!isIgnoredStackTraceLine(element.toString())) {ThrowableProxyUtil.indent(buf, indent);printStackLine(buf, ignoredCount, element);ignoredCount = 0;buf.append(CoreConstants.LINE_SEPARATOR);} else {++ignoredCount;if (maxIndex < stepArray.length) {++maxIndex;}}}if (ignoredCount > 0) {printIgnoredCount(buf, ignoredCount);buf.append(CoreConstants.LINE_SEPARATOR);}if (commonFrames > 0 && unrestrictedPrinting) {ThrowableProxyUtil.indent(buf, indent);buf.append("... ").append(tp.getCommonFrames()).append(" common frames omitted").append(CoreConstants.LINE_SEPARATOR);}}

subjoinSTEPArray遍历StackTraceElementProxy数组，然后挨个判断isIgnoredStackTraceLine，若为false才执行printStackLine

isIgnoredStackTraceLine

    private boolean isIgnoredStackTraceLine(String line) {if (ignoredStackTraceLines != null) {for (String ignoredStackTraceLine : ignoredStackTraceLines) {if (line.contains(ignoredStackTraceLine)) {return true;}}}return false;}

isIgnoredStackTraceLine主要是判断指定line是否包含了ignoredStackTraceLines，包含其中一个即返回true

小结

logback的ThrowableProxyConverter继承了ThrowableHandlingConverter，它定义了evaluatorList、ignoredStackTraceLines属性，它将继承自DynamicConverter的optionList做了划分，第一个option为打印异常堆栈的数，之后的option优先作为evaluatorList，若解析为evaluator为null则作为ignoredStackTraceLines参数。evaluatorList用于evaluate(event)，若有个返回true则返回空字符串，而ignoredStackTraceLines则用于过滤包含这些的异常堆栈。