[blog] flink on zeppelin - part2

_posts/2020-05-25-flink-on-zeppelin-part2.md

@@ -0,0 +1,109 @@
+---
+layout: post
+title:  "Flink on Zeppelin Notebooks for Interactive Data Analysis - Part 2"
+date:   2020-06-23T08:00:00.000Z
+categories: ecosystem
+authors:
+- zjffdu:
+  name: "Jeff Zhang"
+  twitter: "zjffdu"
+---
+
+In a previous post, we introduced the basics of Flink on Zeppelin and how to do Streaming ETL. In this second part of the "Flink on Zeppelin" series of posts, I will share how to 
+perform streaming data visualization via Flink on Zeppelin and how to use Apache Flink UDFs in Zeppelin. 
+
+# Streaming Data Visualization
+
+With [Zeppelin](https://zeppelin.apache.org/), you can build a real time streaming dashboard without writing any line of javascript/html/css code.
+
+Overall, Zeppelin supports 3 kinds of streaming data analytics:
+
+* Single Mode
+* Update Mode
+* Append Mode
+
+### Single Mode
+Single mode is used for cases when the result of a SQL statement is always one row, such as the following example. 
+The output format is translated in HTML, and you can specify a paragraph local property template for the final output content template. 
+And you can use `{i}` as placeholder for the {i}th column of the result.
+
+<center>
+<img src="{{ site.baseurl }}/img/blog/2020-05-25-flink-on-zeppelin-part2/flink_single_mode.gif" width="80%" alt="Single Mode"/>
+</center>
+
+### Update Mode
+Update mode is suitable for the cases when the output format is more than one row, 
+and will always be continuously updated. Here’s one example where we use ``GROUP BY``.
+
+<center>
+<img src="{{ site.baseurl }}/img/blog/2020-05-25-flink-on-zeppelin-part2/flink_update_mode.gif" width="80%" alt="Update Mode"/>
+</center>
+
+### Append Mode
+Append mode is suitable for the cases when the output data is always appended. 
+For instance, the example below uses a tumble window.
+
+<center>
+<img src="{{ site.baseurl }}/img/blog/2020-05-25-flink-on-zeppelin-part2/flink_append_mode.gif" width="80%" alt="Append Mode"/>
+</center>
+
+# UDF
+
+SQL is a very powerful language, especially in expressing data flow. But most of the time, you need to handle complicated business logic that cannot be expressed by SQL.
+In these cases UDFs (user-defined functions) come particularly handy. In Zeppelin, you can write Scala or Python UDFs, while you can also import Scala, Python and Java UDFs.
+Here are 2 examples of Scala and Python UDFs:
+
+* Scala UDF
+
+```scala
+%flink
+
+class ScalaUpper extends ScalarFunction {
+def eval(str: String) = str.toUpperCase
+}
+btenv.registerFunction("scala_upper", new ScalaUpper())
+
+```
+
+* Python UDF
+
+```python
+
+%flink.pyflink
+
+class PythonUpper(ScalarFunction):
+def eval(self, s):
+ return s.upper()
+
+bt_env.register_function("python_upper", udf(PythonUpper(), DataTypes.STRING(), DataTypes.STRING()))
+
+```
+
+After you define the UDFs, you can use them directly in SQL:
+
+* Use Scala UDF in SQL
+
+<center>
+<img src="{{ site.baseurl }}/img/blog/2020-05-25-flink-on-zeppelin-part2/flink_scala_udf.png" width="100%" alt="Scala UDF"/>
+</center>
+
+* Use Python UDF in SQL
+
+<center>
+<img src="{{ site.baseurl }}/img/blog/2020-05-25-flink-on-zeppelin-part2/flink_python_udf.png" width="100%" alt="Python UDF"/>
+</center>
+
+# Summary
+
+In this post, we explained how to perform streaming data visualization via Flink on Zeppelin and how to use UDFs. 
+Besides that, you can do more in Zeppelin with Flink, such as batch processing, Hive integration and more.
+You can check the following articles for more details and here's a list of [Flink on Zeppelin tutorial videos](https://www.youtube.com/watch?v=YxPo0Fosjjg&list=PL4oy12nnS7FFtg3KV1iS5vDb0pTz12VcX) for your reference.
+
+# References
+
+* [Apache Zeppelin official website](http://zeppelin.apache.org)
+* Flink on Zeppelin tutorials - [Part 1](https://medium.com/@zjffdu/flink-on-zeppelin-part-1-get-started-2591aaa6aa47)
+* Flink on Zeppelin tutorials - [Part 2](https://medium.com/@zjffdu/flink-on-zeppelin-part-2-batch-711731df5ad9)
+* Flink on Zeppelin tutorials - [Part 3](https://medium.com/@zjffdu/flink-on-zeppelin-part-3-streaming-5fca1e16754)
+* Flink on Zeppelin tutorials - [Part 4](https://medium.com/@zjffdu/flink-on-zeppelin-part-4-advanced-usage-998b74908cd9)
+* [Flink on Zeppelin tutorial videos](https://www.youtube.com/watch?v=YxPo0Fosjjg&list=PL4oy12nnS7FFtg3KV1iS5vDb0pTz12VcX)