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本文主要研究一下logback的ThrowableProxyConverter
ThrowableHandlingConverter
ch/qos/logback/classic/pattern/ThrowableHandlingConverter.java
代码语言：javascript复制/**
* 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
代码语言：javascript复制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
代码语言：javascript复制 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
代码语言：javascript复制 private void addIgnoreStackTraceLine(String ignoredStackTraceLine) {
if (ignoredStackTraceLines == null) {
ignoredStackTraceLines = new ArrayList<String>();
}
ignoredStackTraceLines.add(ignoredStackTraceLine);
}addIgnoreStackTraceLine则是添加到ignoredStackTraceLines
convert
代码语言：javascript复制 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
代码语言：javascript复制 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
代码语言：javascript复制 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
代码语言：javascript复制 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。
