23.5 Integrating Custom Database Actions

The JSTL database access actions look for the default values set by the configuration settings described in Tables Table 23-5 and Table 23-6.

Table 23-5. Data-source configuration setting

Variable name:	javax.servlet.jsp.jstl.sql.dataSource
Java constant:	Config.SQL_DATA_SOURCE
Java type:	String or javax.sql.DataSource
Set by:	<sql:setDataSource>, context parameter or custom code
Used by:	<sql:query>, <sql:update>, and <sql:transaction>

Table 23-6. Maximum rows configuration setting

Variable name:	javax.servlet.jsp.jstl.sql.maxRows
Java constant:	Config.SQL_MAX_ROWS
Java type:	String or Integer
Set by:	Context parameter or custom code
Used by:	<sql:query>

The data-source setting can be set as a String in this format, in which optional parts are shown between brackets:

url [, [driver] [, [user] [, [password]]]

Commas separate the parts, so if the value for any part contains a comma, it must be escaped with a backslash. This type of value creates a simple DataSource without any pooling capabilities, and is intended only for prototype and low-end applications, as described in Chapter 12. It can also be set to a JNDI path for a DataSource made available by the container or to a DataSource created by custom code, such as a servlet or listener. These options are described in detail in Chapter 24.

The maximum rows setting can be set as a String value for a context parameter or as an Integer by custom code. It can be used to prevent runaway queries, because it sets a limit for how many rows are retrieved for a query result.

There are also two support classes related to the JSTL database actions. The javax.servlet.jsp.jstl.sql.SQLExcecutionTag interface is implemented by the tag handlers for both <sql:query> and <sql:update>. It provides one method that allows a nested custom action to add a value for a parameter placeholder in the SQL statement:

public void addSQLParameter(Object value)

The value must be of a type that is accepted for the corresponding column when set by calling java.sql.PreparedStatement.setObject(int index, Object value).

The ResultSupport class provides methods for converting a JDBC ResultSet into a JSTL Result object, described in Chapter 12:

public static Result toResult(java.sql.ResultSet rs)
public static Result toResult(java.sql.ResultSet rs, int maxRows)

I'll show you an example of how to use it in Chapter 24.