Add setTemplateId method

Closes #59 and #60

Author: eddiezane

README.md

@@ -354,6 +354,14 @@ email.setASMGroupId(1);
 email.setSendAt(1409348513);
 ```
 
+### [Templates](https://sendgrid.com/docs/API_Reference/Web_API_v3/Template_Engine/index.html)
+
+#### setTemplateId
+
+```java
+email.setTemplateId("abc123-def456");
+```
+
 ## Contributing
 
 1. Fork it

build.gradle

@@ -51,6 +51,7 @@ dependencies {
   compile 'org.apache.httpcomponents:httpmime:4.3.4'
   compile 'org.json:json:20140107'
   testCompile group: 'junit', name: 'junit', version: '4.12'
+  testCompile group: 'org.skyscreamer', name: 'jsonassert', version: '1.2.3'
 }
 
 repositories {

src/main/java/com/sendgrid/SendGrid.java

@@ -396,6 +396,16 @@ public int getSendAt() {
             return this.smtpapi.getSendAt();
         }
 
+        /**
+         * Convenience method to set the template
+         * @param templateId
+         */
+        public Email setTemplateId(String templateId) {
+            this.getSMTPAPI().addFilter("templates", "enable", 1);
+            this.getSMTPAPI().addFilter("templates", "template_id", templateId);
+            return this;
+        }
+
         public Email addAttachment(String name, File file) throws IOException, FileNotFoundException {
             return this.addAttachment(name, new FileInputStream(file));
         }

src/test/java/com/sendgrid/SendGridTest.java

@@ -3,6 +3,9 @@
 import java.util.HashMap;
 import java.util.Map;
 
+import org.skyscreamer.jsonassert.JSONAssert;
+
+import org.json.JSONObject;
 import org.junit.Test;
 
 import static org.junit.Assert.*;
@@ -159,6 +162,21 @@ public void testAddHeader() {
         assertEquals(correct, email.getHeaders());
     }
 
+    @Test
+    public void testSetTemplateId() {
+        email = new SendGrid.Email();
+        email.setTemplateId("abc-123");
+
+        String filters = email.getSMTPAPI().jsonString();
+
+        JSONObject obj = new JSONObject();
+        obj.put("filters", new JSONObject().put("templates", new JSONObject()
+                .put("settings", new JSONObject().put("enable", 1)
+                        .put("template_id", "abc-123"))));
+
+        JSONAssert.assertEquals(filters, obj.toString(), false);
+    }
+
     @Test
     public void testSmtpapiToHeader() {
         email = new SendGrid.Email();