Enhance the filter to support filter the exception type name.

src/Filter/ExceptionTypeFilter.cs

@@ -0,0 +1,54 @@
+using log4net.Core;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace log4net.Filter
+{
+    public class ExceptionTypeFilter : FilterSkeleton
+    {
+        public ExceptionTypeFilter()
+        {
+            this.AcceptOnMatch = true;
+        }
+
+        /// <summary>
+        /// Set the exception type name to filter
+        /// </summary>
+        public string ExceptionTypeName { get; set; }
+
+        /// <summary>
+        /// <see cref="FilterDecision.Accept"/> when matching <see cref="ExceptionTypeName"/>
+        /// Default value is true.
+        /// </summary>
+        public bool AcceptOnMatch { get; set; }
+
+        public override FilterDecision Decide(LoggingEvent loggingEvent)
+        {
+            var myExceptionType = Type.GetType(this.ExceptionTypeName, false);
+
+            if (this.ExceptionTypeName != null
+                && myExceptionType != null
+                && loggingEvent.ExceptionObject != null)
+            {
+
+                var myIsMatched = myExceptionType.IsInstanceOfType(loggingEvent.ExceptionObject);
+
+                if (this.AcceptOnMatch)
+                {
+                    if (myIsMatched)
+                        return FilterDecision.Accept;
+                }
+                else
+                {
+                    if (myIsMatched)
+                        return FilterDecision.Deny;
+                }
+            }
+
+            return FilterDecision.Neutral;
+        }
+    }
+}

src/log4net.csproj

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="utf-8"?>
+<?xml version="1.0" encoding="utf-8"?>
 <!--
 
  Licensed to the Apache Software Foundation (ASF) under one
@@ -354,6 +354,7 @@
     <Compile Include="Filter\DenyAllFilter.cs">
       <SubType>Code</SubType>
     </Compile>
+    <Compile Include="Filter\ExceptionTypeFilter.cs" />
     <Compile Include="Filter\FilterDecision.cs">
       <SubType>Code</SubType>
     </Compile>
@@ -805,4 +806,4 @@
     <PostBuildEvent>
     </PostBuildEvent>
   </PropertyGroup>
-</Project>
+</Project>

tests/src/Filter/ExceptionTypeFilterTest.cs

@@ -0,0 +1,118 @@
+/*
+ *
+ * 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.
+ *
+*/
+
+#if NET_2_0
+using System;
+using System.Collections.Generic;
+using System.Xml;
+using log4net.Appender;
+using log4net.Config;
+using log4net.Core;
+using log4net.Filter;
+using log4net.Repository;
+using NUnit.Framework;
+using log4net.Tests.Appender;
+using System.Globalization;
+
+namespace log4net.Tests.Filter
+{
+    [TestFixture]
+    public class ExceptionTypeFilterTest
+    {
+
+#if !NETSTANDARD1_3
+        private CultureInfo _currentCulture;
+        private CultureInfo _currentUICulture;
+
+        [SetUp]
+        public void SetUp()
+        {
+            // set correct thread culture
+            _currentCulture = System.Threading.Thread.CurrentThread.CurrentCulture;
+            _currentUICulture = System.Threading.Thread.CurrentThread.CurrentUICulture;
+            System.Threading.Thread.CurrentThread.CurrentCulture = System.Threading.Thread.CurrentThread.CurrentUICulture = System.Globalization.CultureInfo.InvariantCulture;
+        }
+
+        [TearDown]
+        public void TearDown()
+        {
+            // restore previous culture
+            System.Threading.Thread.CurrentThread.CurrentCulture = _currentCulture;
+            System.Threading.Thread.CurrentThread.CurrentUICulture = _currentUICulture;
+        }
+#endif
+
+        protected ILoggerRepository loggerRepository { get; set; }
+
+        [SetUp]
+        public void SetUpConfiguration()
+        {
+            XmlDocument log4netConfig = new XmlDocument();
+            #region Load log4netConfig
+            log4netConfig.LoadXml(@"
+            <log4net>
+            <appender name=""StringAppender"" type=""log4net.Tests.Appender.StringAppender, log4net.Tests"">
+                <filter type=""log4net.Filter.ExceptionTypeFilter, log4net"">
+                    <ExceptionTypeName value=""log4net.Tests.Filter.ExceptionTypeFilterTestException, log4net.Tests"" />
+                </filter>
+            </appender>
+            <root>
+                <level value=""ALL"" />
+                <appender-ref ref=""MemoryAppender"" />
+            </root>
+            </log4net>");
+            #endregion
+
+            ILoggerRepository rep = LogManager.CreateRepository(Guid.NewGuid().ToString());
+            XmlConfigurator.Configure(rep, log4netConfig["log4net"]);
+
+            loggerRepository = LogManager.CreateRepository(Guid.NewGuid().ToString());
+        }
+
+        [Test]
+        public void TestFilterCustomException()
+        {
+            IAppender[] appenders = LogManager.GetRepository(loggerRepository.Name).GetAppenders();
+            Assert.IsTrue(appenders.Length == 1);
+
+            IAppender appender = Array.Find(appenders, delegate(IAppender a) {
+                    return a.Name == "MemoryAppender";
+                });
+            Assert.IsNotNull(appender);
+
+            StringAppender stringAppender = appender as StringAppender;
+            Assert.IsNotNull(stringAppender);
+
+            ILog log1 = LogManager.GetLogger(loggerRepository.Name, "TestFormatString");
+            Assert.IsNotNull(log1);
+
+            // ***
+            log1.Info("Testing for ExceptionTypeFilterTestException", new ExceptionTypeFilterTestException());
+            Assert.AreEqual("Testing for ExceptionTypeFilterTestException", stringAppender.GetString(), "Test ExceptionTypeFilterTestException can be filter.");
+
+        }
+    }
+
+    public class ExceptionTypeFilterTestException : Exception
+    { }
+
+}
+#endif

tests/src/log4net.Tests.csproj

@@ -190,6 +190,7 @@
     <Compile Include="Core\StringFormatTest.cs">
       <SubType>Code</SubType>
     </Compile>
+    <Compile Include="Filter\ExceptionTypeFilterTest.cs" />
     <Compile Include="Hierarchy\Hierarchy.cs" />
     <Compile Include="Hierarchy\Logger.cs">
       <SubType>Code</SubType>