{"id":3185,"date":"2025-12-24T10:00:35","date_gmt":"2025-12-24T15:00:35","guid":{"rendered":"https:\/\/www.mymiller.name\/wordpress\/?p=3185"},"modified":"2025-12-24T10:00:35","modified_gmt":"2025-12-24T15:00:35","slug":"java-tips-part-3","status":"publish","type":"post","link":"https:\/\/www.mymiller.name\/wordpress\/java_tips\/java-tips-part-3\/","title":{"rendered":"Java Tips Part 3"},"content":{"rendered":"\n

Continuing my Java Tips from experience that I have learned from code reviews to different programming tasks.<\/p>\n\n\n\n

Tip 11: Use Hibernate Statistics<\/h2>\n\n\n\n

Now, this is only for your development profiles\/environments, not for production. Hibernate has built-in statistics on your queries. This will break down how much time is spent along each step in the query. A great tool for performance tuning.<\/p>\n\n\n\n

\nspring.jpa.properties.hibernate.generate_statistics=true\nlogging.level.org.hibernate.stat=DEBUG<\/code><\/pre>\n\n\n\n
Tip 12: Hibernate Slow Query Log<\/h2>\n\n\n\n
Following up using Hibernate Statistics, The difference here is this one is more suited for use on test, and production with a lower impact on performance.  In fact, this is highly recommended to use during performance testing.<\/p>\n\n\n\n
Using this feature you are able to specify what queries to log, if they take over x milliseconds then log the query for you to follow. In the example below we set it to 10ms.  You will need to determine the best value for your application. Also, remember not all queries are built the same.  A query to look up all users in the database won’t be as fast as a query to look up a single field from a single row in an indexed table.<\/p>\n\n\n\n
spring.jpa.properties.hibernate.session.events.log.LOG_QUERIES_SLOWER_THAN_MS=10<\/code><\/pre>\n\n\n\n
Tip 13: Use ResultSetExtractor on Queries<\/h2>\n\n\n\n
Native queries in Hibernate\/JPA result in List<Object[]> as our results.  This is not very clean to work with.  There is a very simple way to handle this, let’s say we have the following query: <\/p>\n\n\n\n
String SQL = \"select first, last from Person\";\r\n      List <Object[]> results = jdbcTemplateObject.query(SQL);<\/code><\/pre>\n\n\n\n
This is going to give you all the records In the Person table, with 2 columns of data “first”, and “last”. Now you have to know that those 2 columns are Strings, that 0 is “first” and 1 is “last”. It would be far easier to push this code directly to a Person object.  So we create a ResultSetExtractor like this:<\/p>\n\n\n\n
\tprivate static final class PersonEtractor implements ResultSetExtractor<List<Person>> {\r\n\r\n\t\t@Override\r\n\t\tpublic List<Person> extractData(ResultSet resultSet) throws SQLException, DataAccessException {\r\n\r\n\t\t\tList<Person> personList= new ArrayList<>();\r\n\r\n\t\t\twhile (resultSet.next()) {\r\n\t\t\t\tPerson person= new Person();\r\n\t\t\t\tperson.setName(resultSet.getString(\"first\"));\r\n\t\t\t\tperson.setType(resultSet.getString(\"last\"));\r\n\t\t\t\tpersonList.add(equipment);\r\n\t\t\t}\r\n\t\t\treturn personList;\r\n\t\t}\r\n\t}\r\n<\/code><\/pre>\n\n\n\n
This is an extractor that is created as a separate class.  We could just as easily create this as an inline function.  However, then we couldn’t reuse the code if we needed to.  Now to use this in our query:<\/p>\n\n\n\n
String SQL = \"select first, last from Person\";\n      List <Object[]> results = jdbcTemplateObject.query(SQL, new PersonExtractor());<\/code><\/pre>\n\n\n\n
Why do this v’s working with the List<Object[]>?<\/p>\n\n\n\n