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This guide walks you through the process of accessing relational data with Spring.
You’ll build an application using Spring’s JdbcTemplate to access data stored in a relational database.
The simple data access logic you will work with below below manages first and last names of customers. To represent this data at the application level, create a Customer class.
src/main/java/hello/Customer.java
link:complete/src/main/java/hello/Customer.java[role=include]Spring provides a template class called JdbcTemplate that makes it easy to work with SQL relational databases and JDBC. Most JDBC code is mired in resource acquisition, connection management, exception handling, and general error checking that is wholly unrelated to what the code is meant to achieve. The JdbcTemplate takes care of all of that for you. All you have to do is focus on the task at hand.
src/main/java/hello/Application.java
link:complete/src/main/java/hello/Application.java[role=include]@SpringBootApplication is a convenience annotation that adds all of the following:
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@Configurationtags the class as a source of bean definitions for the application context. -
@EnableAutoConfigurationtells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings. -
@ComponentScantells Spring to look for other components, configurations, and services in the thehellopackage. In this case, there aren’t any.
The main() method uses Spring Boot’s SpringApplication.run() method to launch an application. Did you notice that there wasn’t a single line of XML? No web.xml file either. This web application is 100% pure Java and you didn’t have to deal with configuring any plumbing or infrastructure.
Spring Boot spots H2, an in-memory relational database engine, and automatically creates a connection. Because we are using spring-jdbc, Spring Boot automatically creates a JdbcTemplate. The @Autowired JdbcTemplate field automatically loads it and makes it available.
This Application class implements Spring Boot’s CommandLineRunner, which means it will execute the run() method after the application context is loaded up.
First, you install some DDL using JdbcTemplate’s `execute method.
Second, you take a list of strings and using Java 8 streams, split them into firstname/lastname pairs in a Java array.
Then you install some records in your newly created table using JdbcTemplate’s `batchUpdate method. The first argument to the method call is the query string, the last argument (the array of Object s) holds the variables to be substituted into the query where the “?” characters are.
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For single insert statements, JdbcTemplate’s `insert method is good. But for multiple inserts, it’s better to use batchUpdate.
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Use ? for arguments to avoid SQL injection attacks by instructing JDBC to bind variables.
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Finally you use the query method to search your table for records matching the criteria. You again use the “?” arguments to create parameters for the query, passing in the actual values when you make the call. The last argument is a Java 8 lambda used to convert each result row into a new Customer object.
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Java 8 lambdas map nicely onto single method interfaces, like Spring’s RowMapper. If you are using Java 7 or earlier, you can easily plug in an anonymous interface implementation and have the same method body as the lambda expresion’s body contains, and it will work with no fuss from Spring.
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https://raw.githubusercontent.com/spring-guides/getting-started-macros/master/build_an_executable_jar_mainhead.adoc https://raw.githubusercontent.com/spring-guides/getting-started-macros/master/build_an_executable_jar_with_both.adoc
You should see the following output:
2015-06-19 10:58:31.152 INFO 67731 --- [ main] hello.Application : Creating tables 2015-06-19 10:58:31.219 INFO 67731 --- [ main] hello.Application : Inserting customer record for John Woo 2015-06-19 10:58:31.220 INFO 67731 --- [ main] hello.Application : Inserting customer record for Jeff Dean 2015-06-19 10:58:31.220 INFO 67731 --- [ main] hello.Application : Inserting customer record for Josh Bloch 2015-06-19 10:58:31.220 INFO 67731 --- [ main] hello.Application : Inserting customer record for Josh Long 2015-06-19 10:58:31.230 INFO 67731 --- [ main] hello.Application : Querying for customer records where first_name = 'Josh': 2015-06-19 10:58:31.242 INFO 67731 --- [ main] hello.Application : Customer[id=3, firstName='Josh', lastName='Bloch'] 2015-06-19 10:58:31.242 INFO 67731 --- [ main] hello.Application : Customer[id=4, firstName='Josh', lastName='Long'] 2015-06-19 10:58:31.244 INFO 67731 --- [ main] hello.Application : Started Application in 1.693 seconds (JVM running for 2.054)
Congratulations! You’ve just used Spring to develop a simple JDBC client.