Make AbstractJsonPatternParser throw an exception for invalid pattern…

… instead of logging an ERROR status (#691)

AbstractJsonPatternParser now throws a JsonPatternException in case of invalid pattern. It is up to the AbstractPatternLayoutJsonProvider to catch the exception, log an error status and decide how it should behave.

Invalid PatternLayout formats are now detected and throw a JsonPatternException as well. Detection is done by inspecting the parsed output returned by the PatternLayout when it is started, looking for the special %PARSER_ERROR marker inserted when it encounters an error.

The previous implementation used to ignore fields with an invalid pattern layout while keeping the other. This results in a partial JSON output with only the valid fields. This behaviour is now changed and the provider reverts to producing nothing in case of bad configuration.

These changes address issue #686.

README.md

@@ -2413,6 +2413,9 @@ LOGGER.info("{\"type\":\"example\",\"msg\":\"example of json message with type\"
 Note that the value that is sent for `line_long` is a number even though in your pattern it is a quoted text.
 And the json_message field value is a json object, not a string.
 
+You can escape an operation by prefixing it with `\` if you don't want it to be interpreted.
+
+
 #### Omitting fields with empty values
 
 The pattern provider can be configured to omit fields with the following _empty_ values:

src/main/java/net/logstash/logback/composite/AbstractPatternJsonProvider.java

@@ -19,6 +19,7 @@
 import java.util.Objects;
 
 import net.logstash.logback.pattern.AbstractJsonPatternParser;
+import net.logstash.logback.pattern.AbstractJsonPatternParser.JsonPatternException;
 import net.logstash.logback.pattern.NodeWriter;
 
 import ch.qos.logback.access.spi.IAccessEvent;
@@ -79,19 +80,28 @@ public void start() {
         if (jsonFactory == null) {
             throw new IllegalStateException("JsonFactory has not been set");
         }
-        initializeNodeWriter();
+
+        try {
+            this.nodeWriter = initializeNodeWriter();
+        } catch (JsonPatternException e) {
+            this.nodeWriter = null;
+            addError("Invalid [pattern]: " + e.getMessage(), e);
+        }
 
         super.start();
     }
 
 
     /**
      * Parses the pattern into a {@link NodeWriter}.
+     * 
+     * @return a {@link NodeWriter}
+     * @throws JsonPatternException thrown in case of invalid pattern
      */
-    private void initializeNodeWriter() {
+    private NodeWriter<Event> initializeNodeWriter() throws JsonPatternException {
         AbstractJsonPatternParser<Event> parser = createParser(this.jsonFactory);
         parser.setOmitEmptyFields(omitEmptyFields);
-        this.nodeWriter = parser.parse(pattern);
+        return parser.parse(pattern);
     }
 
 

src/main/java/net/logstash/logback/composite/accessevent/AccessEventPatternJsonProvider.java

@@ -29,7 +29,7 @@ public class AccessEventPatternJsonProvider extends AbstractPatternJsonProvider<
 
     @Override
     protected AbstractJsonPatternParser<IAccessEvent> createParser(JsonFactory jsonFactory) {
-        return new AccessEventJsonPatternParser(this, jsonFactory);
+        return new AccessEventJsonPatternParser(getContext(), jsonFactory);
     }
 
 }

src/main/java/net/logstash/logback/composite/loggingevent/LoggingEventPatternJsonProvider.java

@@ -29,7 +29,7 @@ public class LoggingEventPatternJsonProvider extends AbstractPatternJsonProvider
 
     @Override
     protected AbstractJsonPatternParser<ILoggingEvent> createParser(JsonFactory jsonFactory) {
-        return new LoggingEventJsonPatternParser(this, jsonFactory);
+        return new LoggingEventJsonPatternParser(getContext(), jsonFactory);
     }
 
 }