SQLData


1   /*
2    * @(#)SQLData.java 1.20 03/12/19
3    *
4    * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package java.sql;
9   
10  /**
11   * The interface used for the custom mapping of an SQL user-defined type (UDT) to
12   * a class in the Java programming language. The class object for a class
13   * implementing the <code>SQLData</code> interface will be entered in the
14   * appropriate <code>Connection</code> object's type map along with the SQL
15   * name of the UDT for which it is a custom mapping.
16   * <P>
17   * Typically, a <code>SQLData</code> implementation
18   * will define a field for each attribute of an SQL structured type or a
19   * single field for an SQL <code>DISTINCT</code> type. When the UDT is
20   * retrieved from a data source with the <code>ResultSet.getObject</code>
21   * method, it will be mapped as an instance of this class.  A programmer
22   * can operate on this class instance just as on any other object in the
23   * Java programming language and then store any changes made to it by
24   * calling the <code>PreparedStatement.setObject</code> method,
25   * which will map it back to the SQL type.
26   * <p>
27   * It is expected that the implementation of the class for a custom
28   * mapping will be done by a tool.  In a typical implementation, the
29   * programmer would simply supply the name of the SQL UDT, the name of
30   * the class to which it is being mapped, and the names of the fields to
31   * which each of the attributes of the UDT is to be mapped.  The tool will use
32   * this information to implement the <code>SQLData.readSQL</code> and
33   * <code>SQLData.writeSQL</code> methods.  The <code>readSQL</code> method
34   * calls the appropriate <code>SQLInput</code> methods to read
35   * each attribute from an <code>SQLInput</code> object, and the
36   * <code>writeSQL</code> method calls <code>SQLOutput</code> methods
37   * to write each attribute back to the data source via an
38   * <code>SQLOutput</code> object.
39   * <P>
40   * An application programmer will not normally call <code>SQLData</code> methods
41   * directly, and the <code>SQLInput</code> and <code>SQLOutput</code> methods
42   * are called internally by <code>SQLData</code> methods, not by application code.
43   * 
44   * @since 1.2
45   */
46  public interface SQLData {
47  
48   /** 
49    * Returns the fully-qualified 
50    * name of the SQL user-defined type that this object represents.
51    * This method is called by the JDBC driver to get the name of the
52    * UDT instance that is being mapped to this instance of 
53    * <code>SQLData</code>.
54    *
55    * @return the type name that was passed to the method <code>readSql</code>
56    *            when this object was constructed and populated
57    * @exception SQLException if there is a database access error
58    * @since 1.2
59    */
60    String   getSQLTypeName() throws SQLException  ;
61  
62   /**
63    * Populates this object with data read from the database.
64    * The implementation of the method must follow this protocol:
65    * <UL> 
66    * <LI>It must read each of the attributes or elements of the SQL
67    * type  from the given input stream.  This is done 
68    * by calling a method of the input stream to read each
69    * item, in the order that they appear in the SQL definition
70    * of the type.  
71    * <LI>The method <code>readSQL</code> then
72    * assigns the data to appropriate fields or 
73    * elements (of this or other objects).
74    * Specifically, it must call the appropriate <i>reader</i> method 
75    * (<code>SQLInput.readString</code>, <code>SQLInput.readBigDecimal</code>,
76    * and so on) method(s) to do the following:
77    * for a distinct type, read its single data element;
78    * for a structured type, read a value for each attribute of the SQL type.
79    * </UL>  
80    * The JDBC driver initializes the input stream with a type map
81    * before calling this method, which is used by the appropriate
82    * <code>SQLInput</code> reader method on the stream.
83    *
84    * @param stream the <code>SQLInput</code> object from which to read the data for
85    * the value that is being custom mapped
86    * @param typeName the SQL type name of the value on the data stream
87    * @exception SQLException if there is a database access error
88    * @see SQLInput
89    */
90    void readSQL (SQLInput   stream, String   typeName) throws SQLException  ;
91  
92    /**
93    * Writes this object to the given SQL data stream, converting it back to
94    * its SQL value in the data source.
95    * The implementation of the method must follow this protocol:<BR>
96    * It must write each of the attributes of the SQL type
97    * to the given output stream.  This is done by calling a 
98    * method of the output stream to write each item, in the order that 
99    * they appear in the SQL definition of the type.
100   * Specifically, it must call the appropriate <code>SQLOutput</code> writer
101   * method(s) (<code>writeInt</code>, <code>writeString</code>, and so on)
102   * to do the following: for a Distinct Type, write its single data element;
103   * for a Structured Type, write a value for each attribute of the SQL type.
104   *
105   * @param stream the <code>SQLOutput</code> object to which to write the data for
106   * the value that was custom mapped
107   * @exception SQLException if there is a database access error
108   * @see SQLOutput
109   * @since 1.2
110   */
111   void writeSQL (SQLOutput   stream) throws SQLException  ;
112 }
113 
114
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