Spring Boot is a great way to get up and running with Spring applications quickly. It provides many features out of the box, including auto-configuration, embedded servers, and starter dependencies.
Spring XD is a tool for building data pipelines. It can ingest data from many sources, process it in various ways, and output it to many sinks.
In this post, we'll learn how to use Spring Boot with Spring XD. We'll start with a simple example that ingests data from a file and outputs it to a database. Then we'll explore some of the more advanced features of Spring XD.
Before we get started, we need to install a few things:
Let's start with a simple example. We'll create a file called data.txt
with the following contents:
Hello, world!
Next, we'll create a Spring XD stream that ingests data from this file and outputs it to the console. We can do this with the following command:
xd:>stream create --name hello --definition "file --dir=./ --pattern=data.txt | log" --deploy
This stream has two components: a file source and a log sink. The file source is configured to read from the ./
directory (the current directory) and look for files with the pattern data.txt
. The log sink simply outputs the data to the console.
We can see the stream running with the following command:
xd:>stream list
And we can see the output of the stream with the following command:
xd:>log hello
In the previous example, we outputted the data to the console. But in many cases, we'll want to output the data to a database. Spring XD makes this easy with the jdbc
sink.
First, we need to create a database. We'll use H2, which is a lightweight database that can run in memory. We can create a database with the following command:
xd:>jdbc create --name mydb --url jdbc:h2:mem:mydb
This will create a database called mydb
in memory.
Next, we need to create a table in this database. We'll use the following SQL:
CREATE TABLE messages (
id IDENTITY,
message VARCHAR(255)
);
We can execute this SQL with the following command:
xd:>jdbc execute --name mydb --sql "CREATE TABLE messages (id IDENTITY, message VARCHAR(255))"
Now we have a database and a table, we can create a stream that outputs the data to this table. We can do this with the following command:
xd:>stream create --name db --definition "file --dir=./ --pattern=data.txt | jdbc --name=mydb --tableName=messages --columns=message" --deploy
This stream is similar to the previous one, but it has a jdbc
sink instead of a log
sink. The jdbc
sink is configured to write to the messages
table in the mydb
database. The columns
property specifies which columns in the table should be populated with data from the stream.
We can verify that the data has been inserted into the database with the following SQL:
SELECT * FROM messages;
In the previous examples, we've seen how to ingest data from a file and output it to either the console or a database. But in many cases, we'll want to process the data in some way before outputting it. Spring XD makes this easy with processors.
Processors can transform the data in any way we want. In this example, we'll create a processor that converts the data to uppercase. We can do this with the following command:
xd:>processor create --name uppercase --definition "transform --expression=payload.toUpperCase()" --deploy
This processor has a single transform
module. The transform
module takes an expression that is evaluated for each piece of data in the stream. In this case, the expression is payload.toUpperCase()
, which converts the data to uppercase.
Now we can modify our db
stream to use this processor:
xd:>stream create --name db --definition "file --dir=./ --pattern=data.txt | uppercase | jdbc --name=mydb --tableName=messages --columns=message" --deploy
We can verify that the data has been inserted into the database with the following SQL:
SELECT * FROM messages;
In this post, we've learned how to use Spring Boot with Spring XD. We've seen how to create a stream that ingests data from a file and outputs it to either the console or a database. And we've seen how to use a processor to transform the data before it is outputted.