Skip to main content

Learning iBATIS - the retrieving Operation

#1 Retrieving

  •  A sample SQL Mapping descriptor



<select id="getAddress"
parameterClass="int"
resultClass="Address">
SELECT
ADR_ID as id,
ADR_DESCRIPTION as description,
ADR_STREET as street,
ADR_CITY as city,
ADR_PROVINCE as province,
ADR_POSTAL_CODE as postalCode
FROM ADDRESS
WHERE ADR_ID = #id#
</select>



  • Usage


Address address = (Address) sqlMap.queryForObject("getAddress", new Integer(5));



  •    How it works
     More than anything else, iBATIS is an alternative to writing JDBC code. API like JDBC are powerful, but tend to be verbose and repetitive. Look at below example,


public Employee getEmployee (int id) throws SQLException {
Employee employee = null;
String sql = "SELECT * FROM EMPLOYEE " +
"WHERE EMPLOYEE_NUMBER = ?";
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = dataSource.getConnection();
ps = conn.prepareStatement(sql);
ps.setInt(1, id);
rs = ps.executeQuery();
employee = null;
while (rs.next()) {
employee = new Employee();
employee.setId(rs.getInt("ID"));
employee.setEmployeeNumber(rs.getInt("EMPLOYEE_NUMBER"));
employee.setFirstName(rs.getString("FIRST_NAME"));
employee.setLastName(rs.getString("LAST_NAME"));
employee.setTitle(rs.getString("TITLE"));
}
} finally {
try {
if (rs != null) rs.close();
} finally {
try {
if (ps != null) ps.close();
} finally {
if (conn != null) conn.close();
}
}
}
return employee;
}

It's easy to see the overhead created by the JDBC API. Every line is necessary, though, so there's no easy way to reduce it. At best, a few of the lines can be extracted into utility methods, most notably the closing of resources such as the PreparedStatement and the ResultSet.

Under the hood, iBATIS will run nearly the same JDBC code. iBATIS will get a connection to the database, set the parameters, execute the statement, retrieve the results, and close all of the resources. However, the amount of code that you need to write is significantly reduced.


As you've seen in earlier examples, it's a very simple single line of code:
Employee emp = (Employee) sqlMap.queryForObject("getEmployee", new Integer(5));

There's nothing to it. This line of code executes the statement, sets the parameters, and retrieves the results as a real java object. The SQL is encapsulated and externalized neatly in a XML File. iBATIS manages all of the resources behind the scenes, and the net effect is the same as the JDBC code we saw above.







Comments

Popular posts from this blog

Stretch a row if data overflows in jasper reports

It is very common that some columns of the report need to stretch to show all the content in that column. But  if you just specify the property " stretch with overflow' to that column(we called text field in jasper report world) , it will just stretch that column and won't change other columns, so the row could be ridiculous. Haven't find the solution from internet yet. So I just review the properties in iReport one by one and find two useful properties(the bold highlighted in example below) which resolve the problems.   example:
<band height="20" splitType="Stretch"> <textField isStretchWithOverflow="true" pattern="" isBlankWhenNull="true"> <reportElement stretchType="RelativeToTallestObject" mode="Opaque" x="192" y="0" width="183" height="20"/> <box leftPadding="2"> <pen lineWidth="0.25"/> …

JasperReports - Configuration Reference

Spring - Operations with jdbcTemplate

This class manages all the database communication and exception handling using a java.sql.Connection that is obtained from the provided DataSource. JdbcTemplate is a stateless and threadsafe class and you can safely instantiate a single instance to be used for each DAO.


Use of Callback Methods
JdbcTemplate is based on a template style of programming common to many other parts of Spring. Some method calls are handled entirely by the JdbcTemplate, while others require the calling class to provide callback methods that contain the implementation for parts of the JDBC workflow. This is another form of Inversion of Control. Your application code hands over the responsibility of managing the database access to the template class. The template class in turn calls back to your application code when it needs some detail processing filled in. These callback methods are allowed to throw a java.sql.SQLException, since the framework will be able to catch this exception and use its built-in excepti…