Add Checker Framework annotations in comments (issue #359).

Putting the annotations in comments allows us to use Java 8 syntax and avoid
depending on the Checker Framework library.  Note that we need to use
org.checkerframework.checker.nullness.qual.Nullable for marking types nullable,
because javax.annotation.Nullable can't be applied to types.

1 files changed, 12 insertions, 2 deletions

diff --git a/contrib/zpages/src/main/java/io/opencensus/contrib/zpages/TraceConfigzZPageHandler.java b/contrib/zpages/src/main/java/io/opencensus/contrib/zpages/TraceConfigzZPageHandler.java
index 9b075b30..5257960d 100644
--- a/contrib/zpages/src/main/java/io/opencensus/contrib/zpages/TraceConfigzZPageHandler.java
+++ b/contrib/zpages/src/main/java/io/opencensus/contrib/zpages/TraceConfigzZPageHandler.java
@@ -16,8 +16,6 @@
 
 package io.opencensus.contrib.zpages;
 
-import static com.google.common.base.Strings.isNullOrEmpty;
-
 import com.google.common.base.Charsets;
 import io.opencensus.trace.config.TraceConfig;
 import io.opencensus.trace.config.TraceParams;
@@ -27,6 +25,11 @@ import java.io.OutputStream;
 import java.io.OutputStreamWriter;
 import java.io.PrintWriter;
 import java.util.Map;
+import javax.annotation.Nullable;
+
+/*>>>
+import org.checkerframework.checker.nullness.qual.EnsuresNonNullIf;
+*/
 
 // TODO(bdrutu): Add tests.
 /**
@@ -167,6 +170,13 @@ final class TraceConfigzZPageHandler extends ZPageHandler {
     }
   }
 
+  // TODO(sebright): Try to use a Checker Framework stub file for the Guava Strings class and use
+  // Strings.isNullOrEmpty instead.
+  /*>>> @EnsuresNonNullIf(result = false, expression = "#1") */
+  private static boolean isNullOrEmpty(@Nullable String str) {
+    return str == null || str.isEmpty();
+  }
+
   // Prints a table to a PrintWriter that shows existing trace parameters.
   private static void emitTraceParamsTable(TraceParams params, PrintWriter out) {
     out.write(