BMP-EJB.rar_EJB Entity

package com.learnweblogic.examples.ch9.bmp; import java.rmi.RemoteException; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import java.util.ArrayList; import java.util.Collection; import javax.ejb.DuplicateKeyException; import javax.ejb.EntityContext; import javax.ejb.EntityBean; import javax.ejb.EJBException; import javax.ejb.NoSuchEntityException; import javax.ejb.ObjectNotFoundException; import javax.ejb.RemoveException; import javax.naming.Context; import javax.naming.InitialContext; import javax.naming.NamingException; import javax.sql.DataSource; // The source files in this book use explicit imports instead of // importing a package.*. While this is a matter of personal // preference, using explicit imports allows the user to quickly scan // the file and learn which package contains a class. public class StudentBean implements EntityBean { // The next three variables are instance variables, but are not tied // to a particular identity/primary key. These variables are set in // the setEntityContext method before the bean has an identity and // are used for the lifetime of the bean instance. private EntityContext ctx; private DataSource dataSource; private String tableName; // The name, ssn, and grade variables are the bean's fields. They // will be initialized in ejbCreate, loaded from the database in // ejbLoad, and stored to the database in ejbStore. The ssn field // is the student's social security number and serves as the primary // key for this bean. private String name; private Integer ssn; // primary key private int grade; // The setEntityContext method receives an EntityContext reference // which it stores in a member variable. It also uses the EJB's // environment context to look up some deployment-specific // parameters. When the EJB is deployed, the deployer will specify // values for the tableName and poolName parameters in the // ejb-jar.xml which match the deployment environment. This allows // these values not to be hard-coded into the bean. The // setEntityContext method also gets a DataSource object from the // environment. This will be used to get database connections from // the connection pool. public void setEntityContext(EntityContext c) { ctx = c; try { Context envCtx = (Context) new InitialContext().lookup("java:/comp/env"); tableName = (String) envCtx.lookup("tableName"); String poolName = (String) envCtx.lookup("poolName"); dataSource = (DataSource) envCtx.lookup("/jdbc/"+poolName); } catch (NamingException ne) { // EJB was not deployed properly throw new EJBException(ne); } } public void unsetEntityContext() { ctx = null; } // The ejbCreate method will initialize the member variables from the // passed parameters and then insert the new entity bean into the // database. If the insert fails, a SQLException will be thrown. // The ejbCreate method then uses its ejbFindByPrimaryKey method to // determine whether the key already exists in the table. If the // key is already present in the table, ejbFindByPrimaryKey will // return successfully, and the ejbCreate method will throw the // DuplicateKeyException to inform the caller. Otherwise, an // EJBException is thrown with the SQLException. public Integer ejbCreate(String name, int ssn, int grade) { this.name = name; this.ssn = new Integer(ssn); this.grade = grade; Connection con = null; PreparedStatement ps = null; try { con = dataSource.getConnection(); ps = con.prepareStatement("insert into "+tableName+ " (name, ssn, grade) values (?,?,?)"); ps.setString(1, name); ps.setInt(2, ssn); ps.setInt(3, grade); ps.executeUpdate(); return this.ssn; } catch (SQLException sqe) { try { ejbFindByPrimaryKey(this.ssn); throw new DuplicateKeyException("A student with social "+ "security number: "+ssn+" already exists."); } catch (Exception Ignore) {} sqe.printStackTrace(); throw new EJBException (sqe); } finally { try { if (ps != null) ps.close(); if (con != null) con.close(); } catch (Exception ignore) {} } } // This implementation requires no post-create initialization so // this required method is empty public void ejbPostCreate(String name, int ssn, int grade) {} // The ejbRemove method is responsible for deleting the instance // from the database. This method uses a SQL delete to delete the instance. public void ejbRemove() throws RemoveException { Connection con = null; PreparedStatement ps = null; try { con = dataSource.getConnection(); ps = con.prepareStatement("delete from "+tableName+ " where ssn=?"); ps.setInt(1, ssn.intValue()); if (ps.executeUpdate() < 1) { throw new RemoveException ("Error removing Student with ssn: "+ssn); } } catch (SQLException sqe) { throw new EJBException (sqe); } finally { try { if(ps != null) ps.close(); if(con != null) con.close(); } catch (Exception ignore) {} } } // ejbLoad reads the entity bean's current state from the database // and assigns the values to its member variables. The primary key // is available from the EntityContext member variable. If the // entity bean no longer exists, NoSuchEntityException is thrown. // This might occur if the entity bean was deleted by another client // or directly from the database. public void ejbLoad() { ssn = (Integer) ctx.getPrimaryKey(); Connection con = null; PreparedStatement ps = null; ResultSet rs = null; try { con = dataSource.getConnection(); ps = con.prepareStatement("select name, grade from " +tableName+ " where ssn=?"); ps.setInt(1, ssn.intValue()); ps.executeQuery(); rs = ps.getResultSet(); if (rs.next()) { name = rs.getString(1); grade = rs.getInt(2); } else { throw new NoSuchEntityException("Student with social "+ "security number: "+ssn+" no longer exists."); } } catch (SQLException sqe) { throw new EJBException(sqe); } finally { try { if (rs != null) rs.close(); if (ps != null) ps.close(); if (con != null) con.close(); } catch (Exception ignore) {} } } // The ejbStore method will be called to write the entity bean's // state back to the database. The primary key field is not written // since primary keys should never change. An optimized version of // this bean could also skip writing the name field since it is // never updated. public void ejbStore() { Connection con = null; PreparedStatement ps = null; try { con = dataSource.getConnection(); ps = con.prepareStatement("update "+tableName+ " SET name=?, grade=? " + " where ssn=?"); ps.setString(1, name); ps.setInt(2, grade); ps.setInt(3, ssn.intValue()); ps.executeUpdate(); } catch (SQLException sqe) { throw new EJBException(sqe); } finally { try { if (ps != null) ps.close(); if (con != null) con.close(); } catch (Exception ignore) {} } } // The ejbActivate and ejbPassivate methods are required by the // EntityBean interface, but this bean does not use these callbacks. public void ejbActivate() {} public void ejbPassivate() {} // The ejbFindByPrimary