Optionally print spans to log in json.

Uses jackson ObjectMapper to log one line json between a prefix and suffix strings.

fixes gh-12

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/MilliSpan.java

@@ -22,30 +22,48 @@ import java.util.List;
 import java.util.Map;
 
 import lombok.Builder;
+import lombok.Data;
 import lombok.Singular;
-import lombok.Value;
-import lombok.experimental.NonFinal;
 
 /**
  * @author Spencer Gibb
  */
-@Value
+@Data
 @Builder
 public class MilliSpan implements Span {
-	private long begin;
-	@NonFinal
+	private final long begin;
 	private long end = 0;
-	private String name;
+	private final String name;
 	private final String traceId;
 	@Singular
 	private List<String> parents;
 	private final String spanId;
-	@NonFinal
 	private boolean remote = false;
-	private Map<String, String> kVAnnotations = new LinkedHashMap<>();
+	private final Map<String, String> kVAnnotations = new LinkedHashMap<>();
 	private final String processId;
 	@Singular
-	private List<TimelineAnnotation> timelineAnnotations = new ArrayList<>();
+	private final List<TimelineAnnotation> timelineAnnotations = new ArrayList<>();
+
+	public MilliSpan(long begin, long end, String name, String traceId, List<String> parents, String spanId, boolean remote, String processId) {
+		this.begin = begin;
+		this.end = end;
+		this.name = name;
+		this.traceId = traceId;
+		this.parents = parents;
+		this.spanId = spanId;
+		this.remote = remote;
+		this.processId = processId;
+	}
+
+	//for serialization
+	private MilliSpan() {
+		this.begin = 0;
+		this.name = null;
+		this.traceId = null;
+		this.parents = null;
+		this.spanId = null;
+		this.processId = null;
+	}
 
 	@Override
 	public synchronized void stop() {

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/TimelineAnnotation.java

@@ -17,12 +17,19 @@
 package org.springframework.cloud.sleuth;
 
 import lombok.Data;
+import lombok.RequiredArgsConstructor;
 
 /**
  * @author Spencer Gibb
  */
 @Data
+@RequiredArgsConstructor
 public class TimelineAnnotation {
 	private final long time;
 	private final String msg;
+
+	private TimelineAnnotation() {
+		this.time = 0;
+		this.msg = null;
+	}
 }

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/slf4j/JsonSlf4jSpanListener.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright 2013-2015 the original author or authors.
+ *
+ * Licensed 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.springframework.cloud.sleuth.slf4j;
+
+import com.fasterxml.jackson.databind.DeserializationFeature;
+import lombok.Data;
+import lombok.SneakyThrows;
+import lombok.extern.slf4j.Slf4j;
+
+import org.springframework.cloud.sleuth.event.SpanStoppedEvent;
+import org.springframework.context.event.EventListener;
+import org.springframework.core.Ordered;
+import org.springframework.core.annotation.Order;
+
+import com.fasterxml.jackson.databind.ObjectMapper;
+
+/**
+ * @author Spencer Gibb
+ */
+@Slf4j
+@Order(Ordered.LOWEST_PRECEDENCE)
+@Data
+public class JsonSlf4jSpanListener {
+
+	private final String prefix;
+	private final String suffix;
+	private final ObjectMapper objectMapper = new ObjectMapper();
+
+	public JsonSlf4jSpanListener() {
+		prefix = "[span]";
+		suffix = "[endspan]";
+		objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
+	}
+
+	@SneakyThrows
+	@EventListener(SpanStoppedEvent.class)
+	public void stop(SpanStoppedEvent event) {
+		log.info("{}{}{}", prefix,
+				objectMapper.writeValueAsString(event.getSpan()),
+				suffix);
+	}
+
+}

spring-cloud-sleuth-core/src/main/java/org/springframework/cloud/sleuth/slf4j/SleuthSlf4jAutoConfiguration.java

@@ -18,6 +18,7 @@ package org.springframework.cloud.sleuth.slf4j;
 
 import org.slf4j.MDC;
 import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
+import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
 import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 
@@ -29,8 +30,15 @@ import org.springframework.context.annotation.Configuration;
 public class SleuthSlf4jAutoConfiguration {
 
 	@Bean
+	@ConditionalOnProperty(value = "spring.cloud.sleuth.listener.slf4j.enabled", matchIfMissing = true)
 	public Slf4jSpanListener slf4jSpanStartedListener() {
 		return new Slf4jSpanListener();
 	}
 
+	@Bean
+	@ConditionalOnProperty("spring.cloud.sleuth.listener.json.slf4j.enabled")
+	public JsonSlf4jSpanListener jsonSlf4jSpanListener() {
+		return new JsonSlf4jSpanListener();
+	}
+
 }

spring-cloud-sleuth-core/src/test/java/org/springframework/cloud/sleuth/slf4j/JsonSlf4jSpanListenerTests.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2013-2015 the original author or authors.
+ *
+ * Licensed 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.springframework.cloud.sleuth.slf4j;
+
+import static org.junit.Assert.*;
+
+import org.junit.Rule;
+import org.junit.Test;
+import org.springframework.boot.test.OutputCapture;
+import org.springframework.cloud.sleuth.MilliSpan;
+import org.springframework.cloud.sleuth.Span;
+import org.springframework.cloud.sleuth.event.SpanStoppedEvent;
+
+import java.io.IOException;
+
+/**
+ * @author Spencer Gibb
+ */
+public class JsonSlf4jSpanListenerTests {
+	@Rule
+	public final OutputCapture output = new OutputCapture();
+
+	@Test
+	public void jsonSpanIsOnOneLine() throws IOException {
+		JsonSlf4jSpanListener listener = new JsonSlf4jSpanListener();
+		Span span = MilliSpan.builder()
+				.name("testSpan")
+				.spanId("spanId1")
+				.parent("parentId1")
+				.traceId("traceId1")
+				.begin(1)
+				.end(10)
+				.build();
+		span.addKVAnnotation("myKey", "myVal");
+		span.addTimelineAnnotation("myTimelineAnnotation");
+		listener.stop(new SpanStoppedEvent(this, span));
+
+		String output = this.output.toString().trim();
+		assertTrue("output doesn't container prefix", output.contains(listener.getPrefix()));
+		assertTrue("output doesn't container suffix", output.contains(listener.getSuffix()));
+
+		int prefixIndex = output.indexOf(listener.getPrefix());
+		int suffixIndex = output.indexOf(listener.getSuffix());
+		String json = output.substring(prefixIndex + listener.getPrefix().length(), suffixIndex);
+		assertFalse("json contains linefeed", output.contains("\n"));
+		assertFalse("json contains carriage return", output.contains("\r"));
+
+		MilliSpan read = listener.getObjectMapper().readValue(json, MilliSpan.class);
+		assertEquals("span not equals", read, span);
+	}
+}