SQL Streamer - Ligthweight SQL Java Stream Adapter

Lightweight SQL to Java Stream API adaptor

Examples

First we setup a SqlStreamer:

1| final java.sql.DataSource ds = ...; // Assume injected in someway
2| final SqlStreamer streamer = SqlStreamer.of(ds.getConnection());

This first example shows, how to do a basic SQL query and process the results using a Java Stream. This example returns a single row, so only one line of output is produced, but of course as a stream its setup to handle any number of results.

SQL:

1| SELECT 1 + 1;

Java:

1| streamer.query()
2|         .select(int.class, "1 + 1") 
3|         .forEach(System.out::println);

Output:

2

Line #	Description
1	creates a query backed by a java.sql.Statement
2	adds a select 1 + 1 clause to the query and int.class maps the SelectStream to an Integer type
3	Stream::forEach(Consumer<Integer> action) is called with each row of the ResultSet produced

Using Tuples

This query selects all columns in table t1 and also executes an SQL AVG() function to average the score. By default if you do not map the select statement result as something else, the default will be a Tuple which can take any number of arbitrary arguments. Also specialized versions of tuples exist for different number of parameters such as Tuple1, Tuple9, etc..

SQL:

1| SELECT AVG(score), t1.* FROM t1 ...;

Java:

1| streamer.query("t1")
2|         .select("AVG(score)", "t1.*")
3|         .forEach(System.out::println);

Prepared Query

Lastly here is an example that shows how use a PreparedStatement backed query. The prepared query can be reused over and over by supplying different values

SQL:

1| SET @skip=1; SET @numrows=5;
2| PREPARE STMT FROM 'SELECT * FROM tbl LIMIT ?, ?';
3| EXECUTE STMT USING @skip, @numrows;

Java:

1| PreparedSqlQuery<Tuple> prepared = streamer.queryBuilder("tbl")
2|         .limit("?", "?")
3|         .build()    // Build a query statement
4|         .prepare(); // Impl: Make it a java.sql.PreparedStatement

---

and now we use the prepared query by supplying the values with values(1, 5) to replace all of the ? in the query. When the .stream() is called, the query is executed and the Stream returned will iterate over the returned ResultSet.

Note that PrearedSqlQuery::stream does not return the enhanced QueryStream, but the normal java.util.stream.Stream which does not allow the prepared query to be further customized.

1| prepared.values(1, 5) // Substitute values for '?'
2|         .stream()     // Execute query and stream over results
3|         .forEach(System.out::println);

For more example please check the examples directory in the repository.