Change internally created StringBuffer and StringBuilder StringAppend…

…erWrapper implementations used by the StringAppender from Singletons to Prototypes.

Fixes bug in StringAppender that maintained stale Log messages in the buffers of the wrappers between tests.

Resolves gh-73.

spring-geode-starter-logging/src/main/java/org/springframework/geode/logging/slf4j/logback/StringAppender.java

@@ -44,40 +44,62 @@ public class StringAppender extends AppenderBase<ILoggingEvent> {
 
 	@FunctionalInterface
 	interface StringAppenderWrapper {
+
 		void append(CharSequence charSequence);
+
+		default void clear() { }
+
 	}
 
-	protected static final StringAppenderWrapper stringBuilderAppenderWrapper = new StringAppenderWrapper() {
+	protected static class StringBufferAppenderWrapper implements StringAppenderWrapper {
 
-		private final StringBuilder stringBuilder = new StringBuilder();
+		protected static StringBufferAppenderWrapper create() {
+			return new StringBufferAppenderWrapper();
+		}
+
+		private final StringBuffer stringBuffer = new StringBuffer();
 
 		@Override
 		public void append(CharSequence charSequence) {
-			this.stringBuilder.append(charSequence);
-			this.stringBuilder.append(NEWLINE);
+			this.stringBuffer.append(charSequence);
+			this.stringBuffer.append(NEWLINE);
+		}
+
+		@Override
+		public void clear() {
+			this.stringBuffer.delete(0, this.stringBuffer.length());
 		}
 
 		@Override
 		public java.lang.String toString() {
-			return this.stringBuilder.toString();
+			return this.stringBuffer.toString();
 		}
-	};
+	}
 
-	protected static final StringAppenderWrapper stringBufferAppenderWrapper = new StringAppenderWrapper() {
+	protected static class StringBuilderAppenderWrapper implements StringAppenderWrapper {
 
-		private final StringBuffer stringBuffer = new StringBuffer();
+		protected static StringBuilderAppenderWrapper create() {
+			return new StringBuilderAppenderWrapper();
+		}
+
+		private final StringBuilder stringBuilder = new StringBuilder();
 
 		@Override
 		public void append(CharSequence charSequence) {
-			this.stringBuffer.append(charSequence);
-			this.stringBuffer.append(NEWLINE);
+			this.stringBuilder.append(charSequence);
+			this.stringBuilder.append(NEWLINE);
+		}
+
+		@Override
+		public void clear() {
+			this.stringBuilder.delete(0, this.stringBuilder.length());
 		}
 
 		@Override
 		public java.lang.String toString() {
-			return this.stringBuffer.toString();
+			return this.stringBuilder.toString();
 		}
-	};
+	}
 
 	@SuppressWarnings({ "rawtypes", "unchecked", "unused" })
 	public static class Builder {
@@ -148,7 +170,10 @@ private String resolveName() {
 		}
 
 		private StringAppenderWrapper resolveStringAppenderWrapper() {
-			return this.useSynchronization ? stringBufferAppenderWrapper : stringBuilderAppenderWrapper;
+
+			return this.useSynchronization
+				? StringBufferAppenderWrapper.create()
+				: StringBuilderAppenderWrapper.create();
 		}
 
 		public StringAppender build() {

spring-geode-starter-logging/src/test/java/org/springframework/geode/logging/slf4j/logback/StringAppenderUnitTests.java

@@ -74,7 +74,8 @@ public void buildStringAppender() {
 		assertThat(stringAppender.isStarted()).isFalse();
 		assertThat(stringAppender.getContext()).isEqualTo(LoggerFactory.getILoggerFactory());
 		assertThat(stringAppender.getName()).isEqualTo(StringAppender.DEFAULT_NAME);
-		assertThat(stringAppender.getStringAppenderWrapper()).isSameAs(StringAppender.stringBuilderAppenderWrapper);
+		assertThat(stringAppender.getStringAppenderWrapper())
+			.isInstanceOf(StringAppender.StringBuilderAppenderWrapper.class);
 	}
 
 	@Test
@@ -116,7 +117,8 @@ public void buildAndStartStringAppender() {
 		assertThat(stringAppender.isStarted()).isTrue();
 		assertThat(stringAppender.getContext()).isEqualTo(mockContext);
 		assertThat(stringAppender.getName()).isEqualTo("TestStringAppender");
-		assertThat(stringAppender.getStringAppenderWrapper()).isEqualTo(StringAppender.stringBufferAppenderWrapper);
+		assertThat(stringAppender.getStringAppenderWrapper())
+			.isInstanceOf(StringAppender.StringBufferAppenderWrapper.class);
 		assertThat(rootLogger.getAppender("TestStringAppender")).isEqualTo(stringAppender);
 
 		verify(delegate, times(1)).setAppender(isA(CompositeAppender.class));