Spring JDBC Dao SQL ‘SELECT’ statement examples

Spring JDBC/Dao FAQ: Can you share some Spring JDBC examples, specifically SQL SELECT query examples using Spring Dao objects?

Sure. I've done a lot of work with The Spring Framework lately, and I love the Spring Dao approach, so this page is a collection of Spring JDBC SELECT query examples (Spring DAO examples) from a real-world Java project I've been working on. In each example I try to show each type of SQL SELECT query that I've used in that project, with a brief explanation before each SQL query.

(The project is a Java-based web interface for the open source Nagios project, but that doesn't matter too much. I just wanted to explain why you're going to see the name "Nagios" in these examples.)

You'll see that many of these examples refer to a NagiosRowMapper. I show the code for that RowMapper (which is an instance of the Spring Framework ParameterizedRowMapper) near the end of this blog post, so you can refer to it as needed.

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Spring JDBC/Dao example #1: Perform a query for exactly one field

In this first Spring Dao example, I use Spring JDBC to get exactly one String field from one record. That is, this Spring DAO method shows how to return one String, not a list of String items:

// spring jdbc select example (returns a String)
public String getNagiosHostTemplateNameById(int hostTemplateId)
{
  String SELECT = " SELECT name "
                + " FROM hosts"
                + " WHERE is_template=true AND id = :id";
  SqlParameterSource namedParameters = new MapSqlParameterSource("id", hostTemplateId);
  return (String)getSimpleJdbcTemplate().queryForObject(SELECT, String.class, namedParameters);
}
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Spring DAO example #2: How to perform a query for one complex object

In this Spring Dao example, I perform a JDBC SELECT query for the given hostId, and then return a complex object (a NagiosHost object) from the query results:

// spring jdbc select example (returns an Object)
public NagiosHost getNagiosHostById(int hostId) 
{
  System.err.println("\nENTERED BaseNagiosHostDao::getNagiosHostById");
  String SELECT = " SELECT * "
                + " FROM hosts"
                + " WHERE is_template=false AND id = :id";
  SqlParameterSource namedParameters = new MapSqlParameterSource("id", hostId);
  return (NagiosHost)getSimpleJdbcTemplate().queryForObject(SELECT, new NagiosHostMapper(), namedParameters);
}
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Example #3: Pass a parameter in, get a list/collection back

In this next Spring Dao example, I perform a JDBC SELECT query for the given hostId, and then return a list of complex objects (NagiosHost objects) from the query results:

// spring jdbc select example (returns a List)
public List getAllHostsExceptGivenId(int hostId) 
{
  String SELECT = " SELECT * FROM hosts "
    + " WHERE is_template=false"
    + " AND id <> ?"
    + " ORDER BY host_name";

  return getSimpleJdbcTemplate().query(SELECT, new NagiosHostMapper(), new Object[]{hostId} );
}
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Example #4: Pass in no parameters and get a list/collection back

In this next Spring JDBC example, I return a list of all NagiosHost objects from a SQL SELECT statement:

// spring jdbc select example (returns a List)
public List getAllHosts() 
{
  String SELECT_ALL = " SELECT * FROM hosts "
    + " WHERE is_template=false" 
    + " ORDER BY host_name";

  return getSimpleJdbcTemplate().query(SELECT_ALL, new NagiosHostMapper());
}
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Example #5: Pass in a parameter and query for a record count

In this Spring Dao example, I show how to get a record count that matches the criteria passed in:

// spring jdbc select example
// returns a count of hosts (isTemplate==false) or templates (isTemplate==true)
//
public int getHostCount(boolean isTemplate)
{ 
  String SELECT_COUNT = "SELECT COUNT(0) FROM hosts WHERE is_template = :is_template"; 
  SqlParameterSource namedParameters = new MapSqlParameterSource("is_template", isTemplate); 
  return getSimpleJdbcTemplate().queryForInt(sql, namedParameters);
} 
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Example #6: Query for a record count (no parameters passed in)

In this final Spring JDBC example, I show how to get a record count that matches the criteria passed in:

// spring jdbc select example
// returns a count of hosts (isTemplate==false) or templates (isTemplate==true)
//
public int getHostCount()
{ 
  String SELECT_COUNT = "SELECT COUNT(0) FROM hosts WHERE is_template = false"; 
  SqlParameterSource namedParameters = new MapSqlParameterSource("is_template", isTemplate); 
  return getSimpleJdbcTemplate().queryForInt(sql, namedParameters);
} 
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The Spring RowMapper class needed for the earlier examples

For most of the previous examples referred to a NagiosHostMapper class. The following Spring JDBC example shows most of that class, where I put a comment by the repetitive lines that I've omitted. Just create a class like this as an inner class in your Spring DAO class, and you'll be ready to go.

//
// create this as an inner class in your spring dao class
//
protected static final class NagiosHostMapper implements ParameterizedRowMapper
{
  public NagiosHost mapRow(ResultSet rs, int rowNum)
  throws SQLException 
  {
    NagiosHost host = new NagiosHost();
    host.setId( rs.getInt("id") );
    host.setIsTemplate( rs.getBoolean("is_template") );
    host.setName( rs.getString("name") );
    //
    // i skipped 30+ lines here to keep this short ...
    //
    host.setInitialStateUp( rs.getBoolean("initial_state_up") );
    host.setUpdatedBy( rs.getInt("updated_by_id") );
    host.setUpdatedTime( rs.getTimestamp("updated_time") );
    return host;
  }
}
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Other Spring DAO class details

It may also help to know a few other details about my Spring DAO class. I'll show some of the information here, and then add more details in another blog post when I have more time.

For now, here are the other parts of my Spring DAO class that I think are important:

/**
 * Some details from my Spring DAO class.
 */
public class BaseNagiosHostDao
  extends SimpleJdbcDaoSupport
  implements BaseDao
{
  protected SimpleJdbcTemplate simpleJdbcTemplate;
  protected TransactionTemplate transactionTemplate;  

  // used for dynamic insert statements
  SimpleJdbcInsert insertHost;

  public void setSimpleJdbcTemplate(SimpleJdbcTemplate simpleJdbcTemplate)
  {
    this.simpleJdbcTemplate = simpleJdbcTemplate;
  }

  // spring-injected
  public void setTransactionTemplate(TransactionTemplate transactionTemplate) 
  {
    this.transactionTemplate = transactionTemplate;
  }

  //
  // the rest of the methods i've shown above are in this area ...
  //

}
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