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Apache Log4j Layout for JSON template.
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache license, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the license for the specific language governing permissions and
* limitations under the license.
*/
package org.apache.logging.log4j.layout.template.json.resolver;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.layout.template.json.util.JsonWriter;
import org.apache.logging.log4j.layout.template.json.util.Recycler;
import org.apache.logging.log4j.message.Message;
import org.apache.logging.log4j.message.ParameterConsumer;
import org.apache.logging.log4j.message.ParameterVisitable;
/**
* {@link Message} parameter (i.e., {@link Message#getParameters()}) resolver.
*
* Configuration
*
*
* config = [ stringified ] , [ index ]
* stringified = "stringified" -> boolean
* index = "index" -> number
*
*
* Examples
*
* Resolve the message parameters into an array:
*
*
* {
* "$resolver": "messageParameter"
* }
*
*
* Resolve the string representation of all message parameters into an array:
*
*
* {
* "$resolver": "messageParameter",
* "stringified": true
* }
*
*
* Resolve the first message parameter:
*
*
* {
* "$resolver": "messageParameter",
* "index": 0
* }
*
* Resolve the string representation of the first message parameter:
*
*
* {
* "$resolver": "messageParameter",
* "index": 0,
* "stringified": true
* }
*
*/
public final class MessageParameterResolver implements EventResolver {
private final Recycler parameterConsumerStateRecycler;
private final boolean stringified;
private final int index;
MessageParameterResolver(
final EventResolverContext context,
final TemplateResolverConfig config) {
this.parameterConsumerStateRecycler = context
.getRecyclerFactory()
.create(ParameterConsumerState::new);
this.stringified = config.getBoolean("stringified", false);
final Integer index = config.getInteger("index");
if (index != null && index < 0) {
throw new IllegalArgumentException("was expecting a positive index: " + config);
}
this.index = index == null ? -1 : index;
}
static String getName() {
return "messageParameter";
}
@Override
public void resolve(final LogEvent logEvent, final JsonWriter jsonWriter) {
// If possible, perform a garbage-free resolution.
final Message message = logEvent.getMessage();
if (message instanceof ParameterVisitable) {
final ParameterVisitable parameterVisitable = (ParameterVisitable) message;
resolve(parameterVisitable, jsonWriter);
return;
}
// Short-circuit if there are no parameters.
final Object[] parameters = message.getParameters();
if (parameters == null || parameters.length == 0 || index >= parameters.length) {
if (index < 0) {
jsonWriter.writeArrayStart();
jsonWriter.writeArrayEnd();
} else {
jsonWriter.writeNull();
}
return;
}
// Resolve all parameters.
if (index < 0) {
jsonWriter.writeArrayStart();
for (int i = 0; i < parameters.length; i++) {
if (i > 0) {
jsonWriter.writeSeparator();
}
final Object parameter = parameters[i];
if (stringified) {
final String stringifiedParameter = String.valueOf(parameter);
jsonWriter.writeString(stringifiedParameter);
} else {
jsonWriter.writeValue(parameter);
}
}
jsonWriter.writeArrayEnd();
}
// Resolve a single parameter.
else {
final Object parameter = parameters[index];
if (stringified) {
final String stringifiedParameter = String.valueOf(parameter);
jsonWriter.writeString(stringifiedParameter);
} else {
jsonWriter.writeValue(parameter);
}
}
}
/**
* Perform a garbage-free resolution via {@link ParameterVisitable} interface.
*/
private void resolve(
final ParameterVisitable parameterVisitable,
final JsonWriter jsonWriter) {
final ParameterConsumerState parameterConsumerState =
parameterConsumerStateRecycler.acquire();
try {
final boolean arrayNeeded = index < 0;
if (arrayNeeded) {
jsonWriter.writeArrayStart();
}
final StringBuilder buf = jsonWriter.getStringBuilder();
final int startIndex = buf.length();
parameterConsumerState.resolver = this;
parameterConsumerState.jsonWriter = jsonWriter;
parameterVisitable.forEachParameter(
PARAMETER_CONSUMER, parameterConsumerState);
if (arrayNeeded) {
jsonWriter.writeArrayEnd();
} else if (startIndex == buf.length()) {
// Handle the case in which index was not present in the event.
jsonWriter.writeNull();
}
} finally {
parameterConsumerStateRecycler.release(parameterConsumerState);
}
}
private static final class ParameterConsumerState {
private MessageParameterResolver resolver;
private JsonWriter jsonWriter;
private ParameterConsumerState() {}
}
private static final ParameterConsumer PARAMETER_CONSUMER =
(final Object parameter, final int index, final ParameterConsumerState state) -> {
// Write the separator, if needed.
final boolean arrayNeeded = state.resolver.index < 0;
if (arrayNeeded && index > 0) {
state.jsonWriter.writeSeparator();
}
// Write the value.
if (arrayNeeded || state.resolver.index == index) {
if (state.resolver.stringified) {
final String stringifiedParameter = String.valueOf(parameter);
state.jsonWriter.writeString(stringifiedParameter);
} else {
state.jsonWriter.writeValue(parameter);
}
}
};
}