Start adding a Logback demo for opencensus-contrib-log-correlation-st…

…ackdriver (Java).

This commit adds a demo for log correlation using OpenCensus, Logback, and
Stackdriver.  It is very similar to the demo that was originally contained in
census-instrumentation/opencensus-java#1212.

The demo can be run with `./gradlew run` in the
`java/log_correlation/stackdriver/logback/` directory.

java/log_correlation/stackdriver/logback/README.md

@@ -0,0 +1,12 @@
+# OpenCensus/Logback/Stackdriver Log Correlation Demo
+
+An application that demonstrates log correlation in Stackdriver with
+`opencensus-contrib-log-correlation-stackdriver`. The application contains SLF4J log statements and
+OpenCensus tracing instrumentation. It configures logging with a Logback XML configuration and
+exports logs using the
+[Stackdriver Logging Logback appender](https://cloud.google.com/logging/docs/setup/java#logback_appender).
+It also exports traces using `opencensus-exporter-trace-stackdriver`, so that Stackdriver can show
+the log entries associated with each trace.
+
+The application requires a Google Cloud project with Stackdriver Logging enabled. It can be run with
+`./gradlew run`.

java/log_correlation/stackdriver/logback/build.gradle

@@ -0,0 +1,32 @@
+description = 'OpenCensus/Logback/Stackdriver Log Correlation Demo'
+
+apply plugin: 'java'
+
+repositories {
+    mavenCentral()
+}
+
+group = "io.opencensus"
+version = "0.16.0-SNAPSHOT"
+
+def opencensusVersion = "0.15.0"
+
+tasks.withType(JavaCompile) {
+    sourceCompatibility = '1.7'
+    targetCompatibility = '1.7'
+}
+
+dependencies {
+    compile "io.opencensus:opencensus-api:${opencensusVersion}",
+            "io.opencensus:opencensus-exporter-trace-stackdriver:${opencensusVersion}",
+            "org.slf4j:slf4j-api:1.7.25"
+
+    runtime "io.opencensus:opencensus-contrib-log-correlation-stackdriver:${opencensusVersion}",
+            "io.opencensus:opencensus-impl-lite:${opencensusVersion}",
+            "com.google.cloud:google-cloud-logging-logback:0.48.0-alpha"
+}
+
+apply plugin: 'application'
+
+mainClassName =
+    'io.opencensus.demo.logcorrelation.stackdriver.logback.OpenCensusTraceLoggingEnhancerDemo'

java/log_correlation/stackdriver/logback/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.9-bin.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

java/log_correlation/stackdriver/logback/gradlew

@@ -0,0 +1,172 @@
+#!/usr/bin/env sh
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS=""
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=$(save "$@")
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
+if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
+  cd "$(dirname "$0")"
+fi
+
+exec "$JAVACMD" "$@"

java/log_correlation/stackdriver/logback/gradlew.bat

@@ -0,0 +1,84 @@
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS=
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

java/log_correlation/stackdriver/logback/src/main/java/io/opencensus/demo/logcorrelation/stackdriver/logback/OpenCensusTraceLoggingEnhancerDemo.java

@@ -0,0 +1,89 @@
+/*
+ * Copyright 2018, OpenCensus 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 io.opencensus.demo.logcorrelation.stackdriver.logback;
+
+import io.opencensus.common.Scope;
+import io.opencensus.exporter.trace.stackdriver.StackdriverTraceConfiguration;
+import io.opencensus.exporter.trace.stackdriver.StackdriverTraceExporter;
+import io.opencensus.trace.Sampler;
+import io.opencensus.trace.Tracer;
+import io.opencensus.trace.Tracing;
+import io.opencensus.trace.samplers.Samplers;
+import java.io.IOException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/** Demo for {@code OpenCensusTraceLoggingEnhancer} using SLF4J and Logback. */
+public final class OpenCensusTraceLoggingEnhancerDemo {
+
+  private static final Logger logger =
+      LoggerFactory.getLogger(OpenCensusTraceLoggingEnhancerDemo.class.getName());
+
+  private static final Tracer tracer = Tracing.getTracer();
+
+  private OpenCensusTraceLoggingEnhancerDemo() {}
+
+  /**
+   * Runs the demo. It creates a sampled and a non-sampled trace to demonstrate how log correlation
+   * handles both cases.
+   */
+  public static void main(String[] args) throws IOException {
+    StackdriverTraceExporter.createAndRegister(StackdriverTraceConfiguration.builder().build());
+    createSampledTrace();
+    createNonSampledTrace();
+    Tracing.getExportComponent().shutdown();
+  }
+
+  private static void createSampledTrace() {
+    doWork(Samplers.alwaysSample());
+  }
+
+  private static void createNonSampledTrace() {
+    doWork(Samplers.neverSample());
+  }
+
+  private static void doWork(Sampler sampler) {
+    try (Scope scope = tracer.spanBuilder("ParentSpan").setSampler(sampler).startScopedSpan()) {
+      pause();
+      logger.warn("parent span log message 1");
+      pause();
+      doMoreWork();
+      pause();
+      logger.info("parent span log message 2");
+      pause();
+    }
+  }
+
+  private static void doMoreWork() {
+    try (Scope scope = tracer.spanBuilder("ChildSpan").startScopedSpan()) {
+      pause();
+      logger.info("child span log message 1");
+      pause();
+      logger.error("child span log message 2");
+      pause();
+    }
+  }
+
+  /** Sleeps for 500 ms to spread out the events on the trace. */
+  private static void pause() {
+    try {
+      Thread.sleep(500);
+    } catch (InterruptedException e) {
+      // ignore
+    }
+  }
+}