jdbcresultset.java

纯Java的数据库

 * who must work under JDK 1.1.x due to operating constraints, yet wish to
 * use some of the more advanced features available under the JDBC 2
 * specification.<p>
 *
 * (fredt@users) <br>
 * (boucherb@users)<p>
 *
 * </div>
 * @see jdbcStatement#executeQuery
 * @see jdbcStatement#getResultSet
 * @see <a href=
 * "http://java.sun.com/j2se/1.4/docs/api/java/sql/ResultSetMetaData.html">
 * <code>ResultSetMetaData</code></a>
 *
 * Extensively rewritten and extended in successive versions of HSQLDB.
 *
 * @author Thomas Mueller (Hypersonic SQL Group)
 * @version 1.8.0
 * @since Hypersonic SQL
 */
public class jdbcResultSet implements ResultSet {

// fredt@users 20020320 - patch 497714 by lakuhns@users - scrollable ResultSet
// variable values in different states
// Condition definitions
//                  bInit  iCurrentRow  nCurrent  nCurrent.next
//                  -----  -----------  --------  -------------
// beforeFirst      false       0         N/A          N/A
// first            true        1        !null    next or null
// last             true    last row #   !null        null
// afterLast        true   last row + 1   N/A         N/A
//------------------------ Private Attributes --------------------------
/*
 * Campbell's comments
 * Future Development Information for Developers and Contributors<p>
 * Providing a
 * full and robust implementation guaranteeing consistently accurate
 * results and behaviour depends upon introducing several new engine
 * features for which the internals of the product currently have no
 * infrastructure: <p>
 *
 * <OL>
 * <LI>a unique rowid for each row in the database which lasts the life
 *  of a row, independent of any updates made to that row</LI>
 * <LI>the ability to explicitly lock either the tables or the
 *  individual rows of an updateable result, for the duration that
 *  the result is open</LI>
 * <LI>the ability to choose between transactions supporting repeatable
 *  reads, committed reads, and uncommitted reads
 * <LI>the ability to map an updated result row's columns back to
 *  specific updateable objects on the database.<p>
 *
 *  <B>Note:</B> Typically, it is easy to do this mapping if all the
 *  rows of a result consist of columns from a single table.  And it
 *  is especially easy if the result's columns are a superset of the
 *  primary key columns of that table.  The ability to
 *  update a result consisting of any combintation of join, union,
 *  intersect, difference and grouping operations, however, is much more
 *  complex to implement and often impossible, especially under
 *  grouping and non-natural joins.  Also, it is not even guaranteed
 *  that the columns of a result map back to *any* updateable object
 *  on the database, for instance in the cases where the
 *  result's column values are general expressions or the result
 *  comes from a stored procedure where the data may not even come,
 *  directly or indirectly, from updateable database objects such as
 *  columns in table rows.
 * </OL>
 *
 * For developers working under a JDBC3 environment,
 * it is gently recommended to take a look at Sun's early access
 * <a href="http://developer.java.sun.com/developer/earlyAccess/crs/">
 * <code>RowSet</code></a> implementation, as this can be used to add
 * JDBC driver independent scrollablility and updateability.
 * However, as a driver independent implementation, it obviously cannot
 * guarantee to use the traditional table and/or row locking features
 * that many DBMS make available to ensure the success of all
 * valid updates against updateable results sets.  As such, performing
 * updates through Sun's early access <code>RowSet</code> implementation
 * may not always succeed, even when it is generally expected that they
 * should.  This is because the condition used to find the original row
 * on the database to update (which, for a driver independent
 * implementation, would have to be equality on all columns values of
 * the originally retrieved row) can become invalid if another
 * transaction modifies or deletes that row on the database at some
 * point between the time the row was last retrieved or refreshed in
 * the RowSet and the time the RowSet attempts to make its next
 * update to that row.  Also, any driver independent implementation
 * of RowSet is still dependent on each driver guaranteeing that its
 * <code>ResultSet</code> objects return completely accurate
 * <code>ResultSetMetaData</code> that fulfills all of the
 * JDBC <code>ResultSetMetaData</code> contracts under all circumstances.
 * However, up to and including 1.7.0, HSQLDB does not make such guarantees
 * under all conditions. See the discussion at {@link #getMetaData}.
 * (boucherb@users) (version 1.7.0)<p>
*/

// boucherb@users/hiep256@users 20010829 - patch 1.7.2 - allow expression to
// return Results as Object, where object is Result or jdbcResultSet.
// - rResult access changed to allow getting internal result object
// from Parser.processCall()

    /** Statement is closed when its result set is closed */
    boolean autoClose;

    /** The internal representation. */
    public Result rResult;

    /**
     * The current record containing the data for the row
     */
    private Record nCurrent;

    /** The row upon which this ResultSet is currently positioned. */
    private int iCurrentRow;

    /** When the result of updating the database, the number of updated rows. */
    private int iUpdateCount;

    /** Is current row before the first row? */
    private boolean bInit;    // false if before first row

    /** How many columns does this ResultSet have? */
    int iColumnCount;

    /** Did the last getXXX method encounter a null value? */
    private boolean bWasNull;

    /** The ResultSetMetaData object for this ResultSet */
    private ResultSetMetaData rsmd;

    /** Properties of this ResultSet's parent Connection. */
    private HsqlProperties connProperties;

    /** is the connection via network */
    private boolean isNetConn;

    /**
     * The Statement that generated this result. Null if the result is
     * from DatabaseMetaData<p>
     */
    jdbcStatement sqlStatement;

    //------------------------ Package Attributes --------------------------

    /**
     * The scrollability / scroll sensitivity type of this result.
     */
    int rsType = TYPE_FORWARD_ONLY;

    /**
     * <!-- start generic documentation -->
     * Moves the cursor down one row from its current position.
     * A <code>ResultSet</code> cursor is initially positioned
     * before the first row; the first call to the method
     * <code>next</code> makes the first row the current row; the
     * second call makes the second row the current row, and so on.
     *
     * <P>If an input stream is open for the current row, a call
     * to the method <code>next</code> will
     * implicitly close it. A <code>ResultSet</code> object's
     * warning chain is cleared when a new row is read. <p>
     *
     * <!-- end generic documentation -->
     *
     * @return <code>true</code> if the new current row is valid;
     * <code>false</code> if there are no more rows
     * @exception SQLException if a database access error occurs
     */
    public boolean next() throws SQLException {

        bWasNull = false;

        // Have an empty resultset so exit with false
        if (rResult == null || rResult.isEmpty()) {
            return false;
        }

        if (!bInit) {

            // The resultset has not been traversed, so set the cursor
            // to the first row (1)
            nCurrent    = rResult.rRoot;
            bInit       = true;
            iCurrentRow = 1;
        } else {

            // The resultset has been traversed, if afterLast, return false
            if (nCurrent == null) {
                return false;
            }

            // On a valid row so go to next
            nCurrent = nCurrent.next;

            iCurrentRow++;
        }

        // finally test to see if we are in an afterLast situation
        if (nCurrent == null) {

            // Yes, set the current row to after last and exit with false
            iCurrentRow = rResult.getSize() + 1;

            return false;
        } else {

            // Not afterLast, so success
            return true;
        }
    }

    /**
     * <!-- start generic documentation -->
     * Releases this <code>ResultSet</code> object's database and
     * JDBC resources immediately instead of waiting for
     * this to happen when it is automatically closed.
     *
     * <P><B>Note:</B> A <code>ResultSet</code> object
     * is automatically closed by the
     * <code>Statement</code> object that generated it when
     * that <code>Statement</code> object is closed,
     * re-executed, or is used to retrieve the next result from a
     * sequence of multiple results. A <code>ResultSet</code> object
     * is also automatically closed when it is garbage collected. <p>
     * <!-- end generic documentation -->
     *
     * @exception SQLException if a database access error occurs
     */
    public void close() throws SQLException {

        iUpdateCount = -1;
        rResult      = null;

        if (autoClose) {
            sqlStatement.close();
        }
    }

    /**
     * <!-- start generic documentation -->
     * Reports whether
     * the last column read had a value of SQL <code>NULL</code>.
     * Note that you must first call one of the getter methods
     * on a column to try to read its value and then call
     * the method <code>wasNull</code> to see if the value read was
     * SQL <code>NULL</code>. <p>
     * <!-- end generic documentation -->
     *
     * @return <code>true</code> if the last column value read was SQL
     *     <code>NULL</code> and <code>false</code> otherwise
     * @exception SQLException if a database access error occurs
     */
    public boolean wasNull() throws SQLException {
        return bWasNull;
    }

    //======================================================================
    // Methods for accessing results by column index
    //======================================================================

    /**
     * <!-- start generic documentation -->
     * Retrieves the value of the designated column in the current row
     * of this <code>ResultSet</code> object as
     * a <code>String</code> in the Java programming language. <p>
     * <!-- end generic documentation -->
     *
     * @param columnIndex the first column is 1, the second is 2, ...
     * @return the column value; if the value is SQL <code>NULL</code>, the
     * value returned is <code>null</code>
     * @exception SQLException if a database access error occurs
     */
    public String getString(int columnIndex) throws SQLException {
        return (String) getColumnInType(columnIndex, Types.CHAR);
    }

    /**
     * <!-- start generic documentation -->
     * Retrieves the value of the designated column in the current row
     * of this <code>ResultSet</code> object as
     * a <code>boolean</code> in the Java programming language. <p>
     * <!-- end generic documentation -->
     *
     * @param columnIndex the first column is 1, the second is 2, ...
     * @return the column value; if the value is SQL <code>NULL</code>, the
     * value returned is <code>false</code>
     * @exception SQLException if a database access error occurs
     */
    public boolean getBoolean(int columnIndex) throws SQLException {

        Object o = getColumnInType(columnIndex, Types.BOOLEAN);

        return o == null ? false
                         : ((Boolean) o).booleanValue();
    }

    /**
     * <!-- start generic documentation -->
     * Retrieves the value of the designated column in the current row
     * of this <code>ResultSet</code> object as
     * a <code>byte</code> in the Java programming language. <p>
     * <!-- end generic documentation -->
     *
     * @param columnIndex the first column is 1, the second is 2, ...
     * @return the column value; if the value is SQL <code>NULL</code>, the
     * value returned is <code>0</code>
     * @exception SQLException if a database access error occurs
     */
    public byte getByte(int columnIndex) throws SQLException {

        Object o = getColumnInType(columnIndex, Types.TINYINT);

        return o == null ? 0
                         : ((Number) o).byteValue();
    }