org.genericdao

Class GenericViewDAO<B>

java.lang.Object

org.genericdao.GenericViewDAO<B>

public class GenericViewDAO<B>
extends Object

This class is used to read rows of a database table and return them in instances of a JavaBean of type B. Usually, the table is a view created by executing a SQL Join. You provide the SQL, this class creates the JavaBeans. The fields returned must have the same names as the properties of the JavaBean. (The GenericDAO class uses the internal implementation of this class to implement its match() and read() methods.)

Here is an example of a bean representing a student:

 public class Student {
     private String studentId;
     private String firstName;
     private String lastName;
     private double gpa;

     public String getStudentId() {
         return studentId;
     }

     public String getFirstName() {
         return firstName;
     }

     public String getLastName() {
         return lastName;
     }

     public String getGpa() {
         return gpa;
     }

     public void setStudentId(String s) {
         studentId = s;
     }

     public void setFirstName(String s) {
         firstName = s;
     }

     public void setLastName(String s) {
         lastName = s;
     }

     public void setGpa(double d) {
         gpa = d;
     }
 }
 

To use this class, instantiate it in the usual way and then call executeQuery(). Provide a SQL query that produces a table that contains a field for every property of the StudentId JavaBean. To prevent injection attacks, pass user data as separate parameters. Here are some examples:

 String sql = "select studentId, firstName, lastName, gpa from student";
 StudentId[] a = executeQuery(sql);

 String sql = "select studentId, firstName, lastName, gpa from student where firstName='Fred'";
 StudentId[] a = executeQuery(sql);

 String sql = "select studentId, firstName, lastName, gpa from student where firstName=?";
 StudentId[] a = executeQuery(sql, request.getParameter("firstName"));

 String sql = "select student.id as studentId, student.first as firstName, "
         + "student.last as lastName, grades.average as gpa "
         + "from student, grades";
 StudentId[] a = executeQuery(sql);

 String sql = "select student.id as studentId, student.first as firstName, "
         + "student.last as lastName, grades.average as gpa "
         + "from student, grades where student.id=?";
 StudentId[] a = executeQuery(sql, request.getParameter("id"));
 Student s = null;
 if (a.length != 0) {
     s = a[0];
 }
 

Constructor Summary

Constructors

Constructor and Description
GenericViewDAO(Class<B> beanClass, ConnectionPool connectionPool) Constructor

Method Summary

Modifier and Type	Method and Description
B[]	executeQuery(String sql, Object... args) Runs a query using the provided SQL and parameters.
String[]	getPropertyNames()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

GenericViewDAO

public GenericViewDAO(Class<B> beanClass,
                      ConnectionPool connectionPool)
               throws DAOException

Constructor

Parameters:

beanClass - the class description of the bean.

connectionPool - the connection pool to use to manage connections to the database.

Throws:

DAOException - if there are any problems, including problems accessing the database, problems with the bean class, etc.

Method Detail

executeQuery

public B[] executeQuery(String sql,
                        Object... args)
                 throws RollbackException

Runs a query using the provided SQL and parameters.

Parameters:

sql - a SQL query, as would be passed to a PreparedStatement.

args - arguments for the SQL query (if any).

Returns:

an array of beans that contain the data in the rows returned by the SQL query. If no rows are returned by the query, a zero length array is returned. (This method never returns null.)

Throws:

RollbackException - if there are errors in the types of the arguments, or if there is an error accessing the database, including SQLException or deadlock.

getPropertyNames

public String[] getPropertyNames()