buid SQLFlow client by Builder pattern

Author: weiguoz

src/main/java/org/sqlflow/client/SQLFlow.java

@@ -20,14 +20,6 @@
 import proto.Sqlflow.Session;
 
 public interface SQLFlow {
-  /**
-   * Open a channel to the SQLFlow server. The serverUrl argument always ends with a port.
-   *
-   * @param serverUrl an address the SQLFlow server exposed.
-   *     <p>Example: "localhost:50051"
-   */
-  void init(String serverUrl);
-
   /**
    * Submit a task to SQLFlow server. This method return immediately.
    *

src/main/java/org/sqlflow/client/impl/SQLFlowImpl.java

@@ -15,7 +15,6 @@
 
 package org.sqlflow.client.impl;
 
-import com.google.common.annotations.VisibleForTesting;
 import io.grpc.ManagedChannel;
 import io.grpc.ManagedChannelBuilder;
 import io.grpc.StatusRuntimeException;
@@ -32,14 +31,8 @@ public class SQLFlowImpl implements SQLFlow {
   private ManagedChannel channel;
   private SQLFlowGrpc.SQLFlowBlockingStub blockingStub;
 
-  public void init(String serverUrl) {
-    this.channel = ManagedChannelBuilder.forTarget(serverUrl).usePlaintext().build();
-    blockingStub = SQLFlowGrpc.newBlockingStub(channel);
-  }
-
-  @VisibleForTesting
-  public SQLFlowImpl(ManagedChannel channel) {
-    this.channel = channel;
+  private SQLFlowImpl(Builder builder) {
+    this.channel = builder.channel;
     blockingStub = SQLFlowGrpc.newBlockingStub(channel);
   }
 
@@ -80,4 +73,31 @@ public void release() throws InterruptedException {
       throw e;
     }
   }
+
+  public static class Builder {
+    private ManagedChannel channel;
+
+    public static Builder newInstance() {
+      return new Builder();
+    }
+
+    public Builder withChannel(ManagedChannel channel) {
+      this.channel = channel;
+      return this;
+    }
+
+    /**
+     * Open a channel to the SQLFlow server. The serverUrl argument always ends with a port.
+     *
+     * @param serverUrl an address the SQLFlow server exposed.
+     *     <p>Example: "localhost:50051"
+     */
+    public Builder forTarget(String serverUrl) {
+      return withChannel(ManagedChannelBuilder.forTarget(serverUrl).usePlaintext().build());
+    }
+
+    public SQLFlow build() {
+      return new SQLFlowImpl(this);
+    }
+  }
 }

src/test/java/org/sqlflow/client/SQLFlowTest.java

@@ -86,7 +86,7 @@ public void setUp() throws Exception {
 
     ManagedChannel channel =
         grpcCleanup.register(InProcessChannelBuilder.forName(serverName).directExecutor().build());
-    client = new SQLFlowImpl(channel);
+    client = SQLFlowImpl.Builder.newInstance().withChannel(channel).build();
   }
 
   @Test
@@ -98,7 +98,7 @@ public void testSubmit() {
     Session session =
         Session.newBuilder()
             .setUserId(userId)
-            .setDbConnStr("mysql://root@[email protected]:3306/iris")
+            .setDbConnStr("mysql://root:[email protected]:3306/iris")
             .build();
     String jobId = client.submit(session, sql);
     assertEquals(mockJobId(userId, sql), jobId);