MACROMEDIA COLDFUSION 4.5-CFML LANGUAGE Manual do Utilizador descarregar pdf (Página 17)

17Writing CFX Tags with Java

Table 30.12 (continued)

ACTION DESCRIPTION COLUMNS RETURNED

GetProcedureColumns PROCEDURE_NAME, COLUMN_NAME,

COLUMN_TYPE

GetPrimaryKeys A description of primary keys. TABLE_NAME, COLUMN_NAME,

KEY_SEQ

GetIndexInfo ASC_OR_DESC

, COLUMN_NAME,

TABLE_NAME, INDEX_NAME,

NON_UNIQUE, TYPE

NOTE

You can get more specific information about the columns returned by each action by looking through the Java SDK documentation

for the

java.sql.DatabaseMetaData interface.

Writing the Java Code

The <CFX_DatabaseMetaData> tag will use a number of classes and methods from the java.sql pack-

age, which are standard, built-in classes supported by the Java 2 SDK and JRE. It’s not possible for

me to explain everything about these classes in these pages, but here is a quick introduction to the

most important classes used in the next example listing:

■

java.sql.DriverManager. This static class is used to obtain connections to data sources.

Its most important method is

getConnection(), which connects to a database based on a

set of connection arguments (the name and location of the database and so on). Before

the

getConnection() method is called, it is traditional to load a database driver using

Class.forName() (see the Java SDK documentation for details).

■

java.sql.Connection. This class is returned by getConnection() and represents an active

connection to a database. In this example, we will be most interested in its

getMetaData()

method, which returns a DatabaseMetaData object (discussed next).

■

java.sql.DatabaseMetaData. This is the class that the CFX tag is most interested in using.

The various actions supported by the tag (see Table 30.12) map directly to many of this

class’s methods, such as getTables() and getColumns(). These methods all return ResultSet

objects containing the requested information.

■

java.sql.ResultSet. This class is the Java equivalent to a ColdFusion query recordset.

Within the CFX tag, the

ResultSet object returned by DatabaseMetaData is converted to

a ColdFusion query using the methods outlined in Table 30.6.

■

java.sql.ResultSetMetaData. This class is conceptually similar to DatabaseMetaData in

that it returns metadata (column names, data types, and so on), but is smaller in scope

and only returns metadata about a particular

ResultSet, rather than the database as a

whole. This CFX tag uses this class to get the names of the columns in the

ResultSet

returned by DatabaseMetaData.

A description of the indexes in the

database.

A listing of columns returned by

stored procedures. Also includes

information about the procedure’s

input and output parameters.

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