Takes care to not load any types that refer to new ones (#941)

brave/src/main/java/brave/internal/Platform.java

@@ -93,13 +93,24 @@ public void log(String msg, Object param1, @Nullable Throwable thrown) {
 
   /** Attempt to match the host runtime to a capable Platform implementation. */
   static Platform findPlatform() {
-    Platform jre9 = Jre9.buildIfSupported();
-
-    if (jre9 != null) return jre9;
-
-    Platform jre7 = Jre7.buildIfSupported();
+    // Find JRE 9 new methods
+    try {
+      Class zoneId = Class.forName("java.time.ZoneId");
+      Class.forName("java.time.Clock").getMethod("tickMillis", zoneId);
+      return new Jre9(); // intentionally doesn't not access the type prior to the above guard
+    } catch (ClassNotFoundException e) {
+      // pre JRE 8
+    } catch (NoSuchMethodException e) {
+      // pre JRE 9
+    }
 
-    if (jre7 != null) return jre7;
+    // Find JRE 7 new methods
+    try {
+      Class.forName("java.util.concurrent.ThreadLocalRandom");
+      return new Jre7(); // intentionally doesn't not access the type prior to the above guard
+    } catch (ClassNotFoundException e) {
+      // pre JRE 7
+    }
 
     // compatible with JRE 6
     return new Jre6();
@@ -115,7 +126,8 @@ static Platform findPlatform() {
   public abstract long randomLong();
 
   /**
-   * Returns the high 8-bytes for {@link brave.Tracing.Builder#traceId128Bit 128-bit trace IDs}.
+   * Returns the high 8-bytes for {@link brave.Tracing.Builder#traceId128Bit(boolean) 128-bit trace
+   * IDs}.
    *
    * <p>The upper 4-bytes are epoch seconds and the lower 4-bytes are random. This makes it
    * convertible to <a href="http://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-request-tracing.html"></a>Amazon
@@ -136,21 +148,6 @@ public Clock clock() {
   }
 
   static class Jre9 extends Jre7 {
-
-    static Jre9 buildIfSupported() {
-      // Find JRE 9 new methods
-      try {
-        Class zoneId = Class.forName("java.time.ZoneId");
-        Class.forName("java.time.Clock").getMethod("tickMillis", zoneId);
-        return new Jre9();
-      } catch (ClassNotFoundException e) {
-        // pre JRE 8
-      } catch (NoSuchMethodException e) {
-        // pre JRE 9
-      }
-      return null;
-    }
-
     @IgnoreJRERequirement @Override public Clock clock() {
       return new Clock() {
         // we could use jdk.internal.misc.VM to do this more efficiently, but it is internal
@@ -171,18 +168,6 @@ static Jre9 buildIfSupported() {
   }
 
   static class Jre7 extends Platform {
-
-    static Jre7 buildIfSupported() {
-      // Find JRE 7 new methods
-      try {
-        Class.forName("java.util.concurrent.ThreadLocalRandom");
-        return new Jre7();
-      } catch (ClassNotFoundException e) {
-        // pre JRE 7
-      }
-      return null;
-    }
-
     @IgnoreJRERequirement @Override public String getHostString(InetSocketAddress socket) {
       return socket.getHostString();
     }

brave/src/test/java/brave/internal/PlatformTest.java

@@ -42,7 +42,7 @@
 @PowerMockIgnore({"org.apache.logging.*", "javax.script.*"})
 @PrepareForTest({Platform.class, NetworkInterface.class})
 public class PlatformTest {
-  Platform platform = Platform.Jre7.buildIfSupported();
+  Platform platform = new Platform.Jre7();
 
   @Test public void clock_hasNiceToString_jre7() {
     assertThat(platform.clock())
@@ -62,7 +62,7 @@ public class PlatformTest {
     when(System.currentTimeMillis())
         .thenReturn(1465510280_000L); // Thursday, June 9, 2016 10:11:20 PM
 
-    long traceIdHigh = Platform.Jre7.buildIfSupported().nextTraceIdHigh();
+    long traceIdHigh = platform.nextTraceIdHigh();
 
     assertThat(HexCodec.toLowerHex(traceIdHigh)).startsWith("5759e988");
   }

instrumentation/benchmarks/src/main/java/brave/internal/PlatformBenchmarks.java

@@ -36,8 +36,8 @@
 @OutputTimeUnit(TimeUnit.MICROSECONDS)
 public class PlatformBenchmarks {
   static final Platform jre6 = new Platform.Jre6();
-  static final Platform jre7 = Platform.Jre7.buildIfSupported();
-  static final Platform jre9 = Platform.Jre9.buildIfSupported();
+  static final Platform jre7 = new Platform.Jre7();
+  static final Platform jre9 = new Platform.Jre9();
   static final Clock jre7Clock = jre7.clock();
   static final Clock jre9Clock = jre9.clock();
 

instrumentation/servlet/src/main/java/brave/servlet/ServletRuntime.java

@@ -63,7 +63,7 @@ private static ServletRuntime findServletRuntime() {
     try {
       Class.forName("javax.servlet.AsyncEvent");
       HttpServletRequest.class.getMethod("isAsyncStarted");
-      return new Servlet3();
+      return new Servlet3(); // intentionally doesn't not access the type prior to the above guard
     } catch (NoSuchMethodException e) {
       // pre Servlet v3
     } catch (ClassNotFoundException e) {

instrumentation/spring-webmvc/src/main/java/brave/spring/webmvc/WebMvcRuntime.java

@@ -42,7 +42,7 @@ static WebMvcRuntime findWebMvcRuntime() {
     // Find spring-webmvc v3.1 new methods
     try {
       Class.forName("org.springframework.web.method.HandlerMethod");
-      return new WebMvc31();
+      return new WebMvc31(); // intentionally doesn't not access the type prior to the above guard
     } catch (ClassNotFoundException e) {
       // pre spring-webmvc v3.1
     }