sqlinputimpl.java

Mobile 应用程序使用 Java Micro Edition (Java ME) 平台

/*
 * @(#)SQLInputImpl.java	1.7 06/08/06
 *
 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */

package javax.sql.rowset.serial;

import java.sql.*;
import javax.sql.*;
import java.io.*;
import java.math.*;
import java.util.Map;

/**
 * An input stream used for custom mapping user-defined types (UDTs).
 * An <code>SQLInputImpl</code> object is an input stream that contains a
 * stream of values that are the attributes of a UDT.
 * <p>
 * This class is used by the driver behind the scenes when the method 
 * <code>getObject</code> is called on an SQL structured or distinct type 
 * that has a custom mapping; a programmer never invokes
 * <code>SQLInputImpl</code> methods directly. They are provided here as a 
 * convenience for those who write <code>RowSet</code> implementations.
 * <P>
 * The <code>SQLInputImpl</code> class provides a set of
 * reader methods analogous to the <code>ResultSet</code> getter
 * methods.  These methods make it possible to read the values in an
 * <code>SQLInputImpl</code> object.
 * <P>
 * The method <code>wasNull</code> is used to determine whether the
 * the last value read was SQL <code>NULL</code>.
 * <P>When the method <code>getObject</code> is called with an
 * object of a class implementing the interface <code>SQLData</code>,
 * the JDBC driver calls the method <code>SQLData.getSQLType</code>
 * to determine the SQL type of the UDT being custom mapped. The driver
 * creates an instance of <code>SQLInputImpl</code>, populating it with the
 * attributes of the UDT.  The driver then passes the input
 * stream to the method <code>SQLData.readSQL</code>, which in turn
 * calls the <code>SQLInputImpl</code> reader methods
 * to read the attributes from the input stream.
 * @see java.sql.SQLData
 */
public class SQLInputImpl implements SQLInput {

    /**
     * <code>true</code> if the last value returned was <code>SQL NULL</code>;
     * <code>false</code> otherwise.
     */
    private boolean lastValueWasNull;
    
    /**
     * The current index into the array of SQL structured type attributes
     * that will be read from this <code>SQLInputImpl</code> object and 
     * mapped to the fields of a class in the Java programming language.
     */
    private int idx;

    /**
     * The array of attributes to be read from this stream.  The order
     * of the attributes is the same as the order in which they were
     * listed in the SQL definition of the UDT.
     */
    private Object attrib[];

    /**
     * The type map to use when the method <code>readObject</code>
     * is invoked. This is a <code>java.util.Map</code> object in which
     * there may be zero or more entries.  Each entry consists of the
     * fully qualified name of a UDT (the value to be mapped) and the 
     * <code>Class</code> object for a class that implements
     * <code>SQLData</code> (the Java class that defines how the UDT
     * will be mapped).
     */
    private Map map;


    /**
     * Creates an <code>SQLInputImpl</code> object initialized with the
     * given array of attributes and the given type map. If any of the
     * attributes is a UDT whose name is in an entry in the type map,
     * the attribute will be mapped according to the corresponding
     * <code>SQLData</code> implementation.
     *
     * @param attributes an array of <code>Object</code> instances in which
     *        each element is an attribute of a UDT. The order of the 
     *        attributes in the array is the same order in which
     *        the attributes were defined in the UDT definition.
     * @param map a <code>java.util.Map</code> object containing zero or more
     *        entries, with each entry consisting of 1) a <code>String</code>
     *        giving the fully
     *        qualified name of the UDT and 2) the <code>Class</code> object
     *        for the <code>SQLData</code> implementation that defines how
     *        the UDT is to be mapped
     * @throws SQLException if the <code>attributes</code> or the <code>map</code>
     *        is a <code>null</code> value
     */
  
    public SQLInputImpl(Object[] attributes, Map<String,Class<?>> map) 
        throws SQLException 
    {        
        if ((attributes == null) || (map == null)) {
            throw new SQLException("Cannot instantiate a SQLInputImpl " +
            "object with null parameters");
        }        
        // assign our local reference to the attribute stream
        attrib = attributes;
        // init the index point before the head of the stream
        idx = -1;
        // set the map
        this.map = map;
    }
        

    /**
     * Retrieves the next attribute in this <code>SQLInputImpl</code> object 
     * as an <code>Object</code> in the Java programming language.
     *
     * @return the next value in the input stream 
     *         as an <code>Object</code> in the Java programming language
     * @throws SQLException if the read position is located at an invalid
     *         position or if there are no further values in the stream
     */
    private Object getNextAttribute() throws SQLException {
        if (++idx >= attrib.length) {
            throw new SQLException("SQLInputImpl exception: Invalid read " + 
				   "position");
        } else {
            return attrib[idx];
        }
    }


    //================================================================
    // Methods for reading attributes from the stream of SQL data.
    // These methods correspond to the column-accessor methods of
    // java.sql.ResultSet.
    //================================================================

    /**
     * Retrieves the next attribute in this <code>SQLInputImpl</code> object as
     * a <code>String</code> in the Java programming language.
     * <p>
     * This method does not perform type-safe checking to determine if the
     * returned type is the expected type; this responsibility is delegated
     * to the UDT mapping as defined by a <code>SQLData</code>
     * implementation.
     * <p>
     * @return the next attribute in this <code>SQLInputImpl</code> object; 
     *     if the value is <code>SQL NULL</code>, return <code>null</code>
     * @throws SQLException if the read position is located at an invalid
     *     position or if there are no further values in the stream.
     */
    public String readString() throws SQLException {

        String attrib = (String)getNextAttribute();   
        
        if (attrib == null) {
            lastValueWasNull = true;
            return null;
        } else {
            lastValueWasNull = false;
            return attrib;
        }
    }

    /**
     * Retrieves the next attribute in this <code>SQLInputImpl</code> object as
     * a <code>boolean</code> in the Java programming language.
     * <p>
     * This method does not perform type-safe checking to determine if the
     * returned type is the expected type; this responsibility is delegated
     * to the UDT mapping as defined by a <code>SQLData</code>
     * implementation.
     * <p>
     * @return the next attribute in this <code>SQLInputImpl</code> object; 
     *     if the value is <code>SQL NULL</code>, return <code>null</code>
     * @throws SQLException if the read position is located at an invalid
     *     position or if there are no further values in the stream.
     */
    public boolean readBoolean() throws SQLException {

        Boolean attrib = (Boolean)getNextAttribute();

        if (attrib == null) {
            lastValueWasNull = true;
            return false;
        } else {
            lastValueWasNull = false;
            return attrib.booleanValue();
        }
    }

    /**
     * Retrieves the next attribute in this <code>SQLInputImpl</code> object as
     * a <code>byte</code> in the Java programming language.
     * <p>
     * This method does not perform type-safe checking to determine if the
     * returned type is the expected type; this responsibility is delegated
     * to the UDT mapping as defined by a <code>SQLData</code>
     * implementation.
     * <p>
     * @return the next attribute in this <code>SQLInputImpl</code> object; 
     *     if the value is <code>SQL NULL</code>, return <code>null</code>
     * @throws SQLException if the read position is located at an invalid
     *     position or if there are no further values in the stream
     */
    public byte readByte() throws SQLException {
        Byte attrib = (Byte)getNextAttribute();

        if (attrib == null) {
            lastValueWasNull = true;
            return (byte)0;
        } else {
            lastValueWasNull = false;
            return attrib.byteValue();
        }
    }

    /**
     * Retrieves the next attribute in this <code>SQLInputImpl</code> object 
     * as a <code>short</code> in the Java programming language.
     * <P>
     * This method does not perform type-safe checking to determine if the
     * returned type is the expected type; this responsibility is delegated
     * to the UDT mapping as defined by a <code>SQLData</code> implementation.
     * <P>
     * @return the next attribute in this <code>SQLInputImpl</code> object;
     *       if the value is <code>SQL NULL</code>, return <code>null</code>
     * @throws SQLException if the read position is located at an invalid
     *       position or if there are no more values in the stream 
     */
    public short readShort() throws SQLException {
        Short attrib = (Short)getNextAttribute();

        if (attrib == null) {
            lastValueWasNull = true;
            return (short)0;
        } else {
            lastValueWasNull = false;
            return attrib.shortValue();
        }
    }
    
    /**
     * Retrieves the next attribute in this <code>SQLInputImpl</code> object 
     * as an <code>int</code> in the Java programming language.     
     * <P>
     * This method does not perform type-safe checking to determine if the
     * returned type is the expected type; this responsibility is delegated
     * to the UDT mapping as defined by a <code>SQLData</code> implementation.
     * <P>
     * @return the next attribute in this <code>SQLInputImpl</code> object;
     *       if the value is <code>SQL NULL</code>, return <code>null</code>
     * @throws SQLException if the read position is located at an invalid
     *       position or if there are no more values in the stream 
     */
    public int readInt() throws SQLException {
        Integer attrib = (Integer)getNextAttribute();
        
        if (attrib == null) {
            lastValueWasNull = true;
            return (int)0;
        } else {
            lastValueWasNull = false;
            return attrib.intValue();
        }
    }

    /**