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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 skipped
        if (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。