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Refactor RegexFilter to use a plugin builder, restore configurable re… #4119

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Refactor RegexFilter to use a plugin builder, restore configurable re…
ramanathan1504 May 9, 2026
16a78a6
update pr url in change log
ramanathan1504 May 9, 2026
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16 changes: 16 additions & 0 deletions log4j-core-test/src/test/java/org/apache/logging/log4j/core/filter/RegexFilterTest.java
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Expand Up @@ -19,6 +19,7 @@
import static org.hamcrest.CoreMatchers.equalTo;
import static org.hamcrest.MatcherAssert.assertThat;
import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
import static org.junit.jupiter.api.Assertions.assertNotNull;
import static org.junit.jupiter.api.Assertions.assertNull;
import static org.junit.jupiter.api.Assertions.assertSame;
import static org.junit.jupiter.api.Assertions.assertTrue;
Expand All @@ -27,6 +28,9 @@
import org.apache.logging.log4j.core.Filter;
import org.apache.logging.log4j.core.Filter.Result;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.LoggerContext;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.Configurator;
import org.apache.logging.log4j.core.impl.Log4jLogEvent;
import org.apache.logging.log4j.message.Message;
import org.apache.logging.log4j.message.SimpleMessage;
Expand Down Expand Up @@ -91,6 +95,18 @@ void testNoMsg() throws Exception {
assertSame(Filter.Result.DENY, filter.filter(null, Level.DEBUG, null, null, (Object[]) null));
}

@Test
void testPatternFlagsFromConfiguration() {
try (final LoggerContext context =
Configurator.initialize("RegexFilterPatternFlagsTest", "filter/RegexFilterPatternFlagsTest.xml")) {
final Configuration configuration = context.getConfiguration();
final Filter filter = configuration.getFilter();
assertNotNull(filter);
assertThat(filter.filter(null, null, null, (Object) "ERROR", null), equalTo(Result.ACCEPT));
assertThat(filter.filter(null, null, null, (Object) "warn", null), equalTo(Result.DENY));
}
}

@Test
void testParameterizedMsg() throws Exception {
final String msg = "params {} {}";
Expand Down
25 changes: 25 additions & 0 deletions log4j-core-test/src/test/resources/filter/RegexFilterPatternFlagsTest.xml
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@@ -0,0 +1,25 @@
<?xml version="1.0" encoding="UTF-8"?>
<!--
~ 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.
-->
<Configuration status="WARN" name="RegexFilterPatternFlagsTest">
<Filters>
<RegexFilter regex="error" patternFlags="CASE_INSENSITIVE" onMatch="ACCEPT" onMismatch="DENY"/>
</Filters>
<Loggers>
<Root level="INFO"/>
</Loggers>
</Configuration>
123 changes: 90 additions & 33 deletions log4j-core/src/main/java/org/apache/logging/log4j/core/filter/RegexFilter.java
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Expand Up @@ -16,9 +16,7 @@
*/
package org.apache.logging.log4j.core.filter;

import java.lang.reflect.Field;
import java.util.Arrays;
import java.util.Comparator;
import java.util.Locale;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.apache.logging.log4j.Level;
Expand All @@ -29,13 +27,15 @@
import org.apache.logging.log4j.core.config.Node;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.config.plugins.PluginAttribute;
import org.apache.logging.log4j.core.config.plugins.PluginElement;
import org.apache.logging.log4j.core.config.plugins.PluginFactory;
import org.apache.logging.log4j.core.config.plugins.PluginBuilderAttribute;
import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
import org.apache.logging.log4j.core.config.plugins.validation.constraints.Required;
import org.apache.logging.log4j.message.Message;
import org.apache.logging.log4j.message.MessageFormatMessage;
import org.apache.logging.log4j.message.ParameterizedMessage;
import org.apache.logging.log4j.message.StringFormattedMessage;
import org.apache.logging.log4j.message.StructuredDataMessage;
import org.apache.logging.log4j.util.Strings;

/**
* A filter that matches the given regular expression pattern against messages.
Expand Down Expand Up @@ -116,6 +116,11 @@ public String toString() {
return sb.toString();
}

@PluginBuilderFactory
public static Builder newBuilder() {
return new Builder();
}

/**
* Creates a Filter that matches a regular expression.
*
Expand All @@ -130,48 +135,100 @@ public String toString() {
* @param mismatch
* The action to perform when a mismatch occurs.
* @return The RegexFilter.
* @throws IllegalAccessException When there is no access to the definition of the specified member.
* @throws IllegalArgumentException When passed an illegal or inappropriate argument.
*/
// TODO Consider refactoring to use AbstractFilter.AbstractFilterBuilder
@PluginFactory
public static RegexFilter createFilter(
// @formatter:off
@PluginAttribute("regex") final String regex,
@PluginElement("PatternFlags") final String[] patternFlags,
@PluginAttribute("patternFlags") final String[] patternFlags,
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@vy vy May 28, 2026

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This sounds like a breaking API change to me. That is, I guess the following was working, and is broken with this change:

<RegexFilter regex="error" onMatch="ACCEPT" onMismatch="DENY">
  <PatternFlags>
    <tag-name-here-does-not-matter>UNIX_LINES</tag-name-here-does-not-matter>
    <tag-name-here-does-not-matter>DOTALL</tag-name-here-does-not-matter>
  </PatternFlags>
</RegexFilter>

@ramanathan1504, would you mind verifying this, please?

@PluginAttribute("useRawMsg") final Boolean useRawMsg,
@PluginAttribute("onMatch") final Result match,
@PluginAttribute("onMismatch") final Result mismatch)
// @formatter:on
throws IllegalArgumentException, IllegalAccessException {
if (regex == null) {
LOGGER.error("A regular expression must be provided for RegexFilter");
return null;
// @formatter:on
{
final String flags = patternFlags == null ? null : String.join(",", patternFlags);
return RegexFilter.newBuilder()
.setRegex(regex)
.setPatternFlags(flags)
.setUseRawMsg(Boolean.TRUE.equals(useRawMsg))
.setOnMatch(match)
.setOnMismatch(mismatch)
.build();
}

private static int toPatternFlags(final String patternFlags) {
if (Strings.isBlank(patternFlags)) {
return DEFAULT_PATTERN_FLAGS;
}
return new RegexFilter(
Boolean.TRUE.equals(useRawMsg), Pattern.compile(regex, toPatternFlags(patternFlags)), match, mismatch);
int flags = DEFAULT_PATTERN_FLAGS;
for (final String flagName : Strings.splitList(patternFlags)) {
flags |= toPatternFlag(flagName);
}
return flags;
}

private static int toPatternFlags(final String[] patternFlags)
throws IllegalArgumentException, IllegalAccessException {
if (patternFlags == null || patternFlags.length == 0) {
private static int toPatternFlag(final String flagName) {
if (Strings.isBlank(flagName)) {
return DEFAULT_PATTERN_FLAGS;
}
final Field[] fields = Pattern.class.getDeclaredFields();
final Comparator<Field> comparator = (f1, f2) -> f1.getName().compareTo(f2.getName());
Arrays.sort(fields, comparator);
final String[] fieldNames = new String[fields.length];
for (int i = 0; i < fields.length; i++) {
fieldNames[i] = fields[i].getName();
switch (flagName.trim().toUpperCase(Locale.ROOT)) {
case "UNIX_LINES":
return Pattern.UNIX_LINES;
case "CASE_INSENSITIVE":
return Pattern.CASE_INSENSITIVE;
case "COMMENTS":
return Pattern.COMMENTS;
case "MULTILINE":
return Pattern.MULTILINE;
case "LITERAL":
return Pattern.LITERAL;
case "DOTALL":
return Pattern.DOTALL;
case "UNICODE_CASE":
return Pattern.UNICODE_CASE;
case "CANON_EQ":
return Pattern.CANON_EQ;
case "UNICODE_CHARACTER_CLASS":
return Pattern.UNICODE_CHARACTER_CLASS;
default:
return DEFAULT_PATTERN_FLAGS;
}
int flags = DEFAULT_PATTERN_FLAGS;
for (final String test : patternFlags) {
final int index = Arrays.binarySearch(fieldNames, test);
if (index >= 0) {
final Field field = fields[index];
flags |= field.getInt(Pattern.class);
}

public static class Builder extends AbstractFilterBuilder<Builder>
implements org.apache.logging.log4j.core.util.Builder<RegexFilter> {

@PluginBuilderAttribute
@Required(message = "A regular expression must be provided for RegexFilter")
private String regex;

@PluginBuilderAttribute
private String patternFlags;

@PluginBuilderAttribute("useRawMsg")
private boolean useRawMsg;

public Builder setRegex(final String regex) {
this.regex = regex;
return this;
}

public Builder setPatternFlags(final String patternFlags) {
this.patternFlags = patternFlags;
return this;
}

public Builder setUseRawMsg(final boolean useRawMsg) {
this.useRawMsg = useRawMsg;
return this;
}

@Override
public RegexFilter build() {
if (!isValid()) {
return null;
}
return new RegexFilter(
useRawMsg, Pattern.compile(regex, toPatternFlags(patternFlags)), getOnMatch(), getOnMismatch());
}
return flags;
}
}
2 changes: 1 addition & 1 deletion log4j-core/src/main/java/org/apache/logging/log4j/core/filter/package-info.java
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Expand Up @@ -22,7 +22,7 @@
* {@link org.apache.logging.log4j.core.Filter#ELEMENT_TYPE filter}.
*/
@Export
@Version("2.25.3")
@Version("2.26.0")
package org.apache.logging.log4j.core.filter;

import org.osgi.annotation.bundle.Export;
Expand Down
12 changes: 12 additions & 0 deletions src/changelog/.2.x.x/regexfilter_patternflags_builder.xml
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@@ -0,0 +1,12 @@
<?xml version="1.0" encoding="UTF-8"?>
<entry xmlns="https://logging.apache.org/xml/ns"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="https://logging.apache.org/xml/ns https://logging.apache.org/xml/ns/log4j-changelog-0.xsd"
type="fixed">
<issue id="3239" link="https://github.com/apache/logging-log4j2/issues/3239"/>
<issue id="4119" link="https://github.com/apache/logging-log4j2/pull/4119"/>
<description format="asciidoc">
Refactor `RegexFilter` to a plugin builder, restore configurable regex `patternFlags` via a CSV attribute, and avoid `useRawMsg` null-unboxing pitfalls by using a primitive boolean in the builder path.
</description>
</entry>

6 changes: 6 additions & 0 deletions src/site/antora/modules/ROOT/pages/manual/filters.adoc
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Expand Up @@ -767,6 +767,12 @@ Besides the <<common-configuration-attributes,common configuration attributes>>,
| `boolean`
| `false`
| If `true`, for xref:manual/messages.adoc#ParameterizedMessage[`ParameterizedMessage`], xref:manual/messages.adoc#StringFormattedMessage[`StringFormattedMessage`], and xref:manual/messages.adoc#MessageFormatMessage[`MessageFormatMessage`], the message format pattern; for xref:manual/messages.adoc#StructuredDataMessage[`StructuredDataMessage`], the message field will be used as the match target.

| patternFlags
| `String`
|
| Comma-separated list of https://docs.oracle.com/javase/{java-target-version}/docs/api/java/util/regex/Pattern.html[`Pattern`] flag names.
Supported values are `UNIX_LINES`, `CASE_INSENSITIVE`, `COMMENTS`, `MULTILINE`, `LITERAL`, `DOTALL`, `UNICODE_CASE`, `CANON_EQ`, and `UNICODE_CHARACTER_CLASS`.
|===

[WARNING]
Expand Down