Fix logback stacktrace information

Since v3.6.0 the stacktrace feature was not working properly in the logback implementation.
Amongst the missing information was the exception class, the exception message and
suppressed or caused exceptions. The proposed change brings back the original coding
used before v3.6.0, which is also used in the log4j2 implementation.

Signed-off-by: Karsten Schnitter <k.schnitter@sap.com>

Author: KarstenSchnitter

cf-java-logging-support-logback/src/main/java/com/sap/hcp/cf/logback/encoder/JsonEncoder.java

@@ -2,6 +2,7 @@
 
 import java.io.IOException;
 import java.io.OutputStream;
+import java.io.PrintWriter;
 import java.io.StringWriter;
 import java.lang.reflect.InvocationTargetException;
 import java.nio.charset.Charset;
@@ -14,6 +15,9 @@
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
+import ch.qos.logback.classic.spi.IThrowableProxy;
+import ch.qos.logback.classic.spi.ThrowableProxy;
+import com.sap.hcp.cf.logging.common.converter.LineWriter;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.slf4j.Marker;
@@ -330,10 +334,12 @@ private Map<String, Object> collectContextFields(ILoggingEvent event) {
 
     private <P extends ComposerBase> void addStacktrace(ObjectComposer<P> oc, ILoggingEvent event) throws IOException,
                                                                                                    JsonProcessingException {
-        if (event.getThrowableProxy() != null) {
-            List<String> lines = Stream.of(event.getThrowableProxy().getStackTraceElementProxyArray()).map(
-                                                                                                           StackTraceElementProxy::getSTEAsString)
-                                       .collect(Collectors.toList());
+        IThrowableProxy proxy = event.getThrowableProxy();
+        if (proxy != null && ThrowableProxy.class.isAssignableFrom(proxy.getClass())) {
+            Throwable throwable = ((ThrowableProxy) proxy).getThrowable();
+            LineWriter lw = new LineWriter();
+            throwable.printStackTrace(new PrintWriter(lw));
+            List<String> lines = lw.getLines();
             StacktraceLines stacktraceLines = new StacktraceLines(lines);
             ArrayComposer<ObjectComposer<P>> ac = oc.startArrayField(Fields.STACKTRACE);
             if (stacktraceLines.getTotalLineLength() <= maxStacktraceSize) {

cf-java-logging-support-logback/src/test/java/com/sap/hcp/cf/logging/common/TestAppLog.java

@@ -1,10 +1,9 @@
 package com.sap.hcp.cf.logging.common;
 
 import static com.sap.hcp.cf.logging.common.converter.CustomFieldMatchers.hasCustomField;
+import static java.util.Arrays.asList;
 import static org.hamcrest.MatcherAssert.assertThat;
-import static org.hamcrest.Matchers.contains;
-import static org.hamcrest.Matchers.greaterThanOrEqualTo;
-import static org.hamcrest.Matchers.lessThanOrEqualTo;
+import static org.hamcrest.Matchers.*;
 import static org.hamcrest.core.Is.is;
 import static org.hamcrest.core.IsNull.notNullValue;
 
@@ -122,20 +121,17 @@ public void testCustomFieldOverwritesMdc() throws Exception {
 		assertThat(getField(SOME_KEY), is(SOME_OTHER_VALUE));
 	}
 
-	@Test
+    @Test
     public void testStacktrace() {
-        try {
-            Double.parseDouble(null);
-        } catch (Exception ex) {
-            logMsg = "Running testStacktrace()";
-            LOGGER.error(logMsg, ex);
-            assertThat(getMessage(), is(logMsg));
-            assertThat(getField(Fields.COMPONENT_ID), is("-"));
-            assertThat(getField(Fields.COMPONENT_NAME), is("-"));
-            assertThat(getField(Fields.COMPONENT_INSTANCE), is("0"));
-            assertThat(getField(Fields.STACKTRACE), is(notNullValue()));
-            assertThat(getField(Fields.WRITTEN_TS), is(notNullValue()));
-        }
+        logMsg = "Running testStacktrace()";
+        Exception testEx = new Exception("Test-case for Stacktraces.");
+        LOGGER.error(logMsg, testEx);
+        assertThat(getMessage(), is(logMsg));
+        assertThat(getField(Fields.COMPONENT_ID), is("-"));
+        assertThat(getField(Fields.COMPONENT_NAME), is("-"));
+        assertThat(getField(Fields.COMPONENT_INSTANCE), is("0"));
+        assertThat(getField(Fields.STACKTRACE), stringContainsInOrder(asList("java.lang.Exception", "Test-case for Stacktraces.")));
+        assertThat(getField(Fields.WRITTEN_TS), is(notNullValue()));
     }
 
     @Test