Use StringBuilder to create ids

presto-main/src/main/java/com/facebook/presto/execution/StageExecutionId.java

@@ -90,6 +90,14 @@ public int hashCode()
     @JsonValue
     public String toString()
     {
-        return stageId + "." + id;
+        StringBuilder builder = new StringBuilder();
+        appendString(builder);
+        return builder.toString();
+    }
+
+    public void appendString(StringBuilder builder)
+    {
+        stageId.appendString(builder);
+        builder.append(".").append(id);
     }
 }

presto-main/src/main/java/com/facebook/presto/execution/StageId.java

@@ -79,7 +79,15 @@ public int getId()
     @JsonValue
     public String toString()
     {
-        return queryId + "." + id;
+        StringBuilder builder = new StringBuilder();
+        appendString(builder);
+        return builder.toString();
+    }
+
+    public void appendString(StringBuilder builder)
+    {
+        queryId.appendString(builder);
+        builder.append(".").append(id);
     }
 
     @Override

presto-main/src/main/java/com/facebook/presto/execution/TaskId.java

@@ -83,7 +83,15 @@ public QueryId getQueryId()
     @JsonValue
     public String toString()
     {
-        return stageExecutionId + "." + id + "." + attemptNumber;
+        StringBuilder builder = new StringBuilder();
+        appendString(builder);
+        return builder.toString();
+    }
+
+    public void appendString(StringBuilder builder)
+    {
+        stageExecutionId.appendString(builder);
+        builder.append(".").append(id).append(".").append(attemptNumber);
     }
 
     @Override

presto-main/src/test/java/com/facebook/presto/execution/TestId.java

@@ -0,0 +1,36 @@
+/*
+ * 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 com.facebook.presto.execution;
+
+import com.facebook.presto.spi.QueryId;
+import org.testng.annotations.Test;
+
+import static org.testng.Assert.assertEquals;
+
+public class TestId
+{
+    @Test
+    public void testAppendString()
+    {
+        QueryId queryId = new QueryId("foo");
+        StageId stageId = new StageId(queryId, 1);
+        StageExecutionId stageExecutionId = new StageExecutionId(stageId, 2);
+        TaskId taskId = new TaskId(stageExecutionId, 3, 1);
+
+        assertEquals(queryId.toString(), "foo");
+        assertEquals(stageId.toString(), String.format("%s.%s", queryId.getId(), stageId.getId()));
+        assertEquals(stageExecutionId.toString(), String.format("%s.%s.%s", queryId.getId(), stageId.getId(), stageExecutionId.getId()));
+        assertEquals(taskId.toString(), String.format("%s.%s.%s.%s.%s", queryId.getId(), stageId.getId(), stageExecutionId.getId(), taskId.getId(), taskId.getAttemptNumber()));
+    }
+}

presto-spi/src/main/java/com/facebook/presto/spi/QueryId.java

@@ -58,6 +58,11 @@ public String toString()
         return id;
     }
 
+    public void appendString(StringBuilder builder)
+    {
+        builder.append(id);
+    }
+
     @Override
     public int hashCode()
     {