CompositeDataView


1   /*
2    * @(#)CompositeDataView.java   1.5 06/03/29
3    * 
4    * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package javax.management.openmbean;
9   
10  /**
11   * <p>A Java class can implement this interface to indicate how it is
12   * to be converted into a {@code CompositeData} by the MXBean framework.</p>
13   *
14   * <p>A typical way to use this class is to add extra items to the
15   * {@code CompositeData} in addition to the ones that are declared in the
16   * {@code CompositeType} supplied by the MXBean framework.  To do this,
17   * you must create another {@code CompositeType} that has all the same items,
18   * plus your extra items.</p>
19   *
20   * <p>For example, suppose you have a class {@code Measure} that consists of
21   * a String called {@code units} and a {@code value} that is either a
22   * {@code long} or a {@code double}.  It might look like this:</p>
23   *
24   * <pre>
25   * public class Measure implements CompositeDataView {
26   *     private String units;
27   *     private Number value; // a Long or a Double
28   *
29   *     public Measure(String units, Number value) {
30   *         this.units = units;
31   *         this.value = value;
32   *     }
33   *
34   *     public static Measure from(CompositeData cd) {
35   *         return new Measure((String) cd.get("units"),
36   *                            (Number) cd.get("value"));
37   *     }
38   *
39   *     public String getUnits() {
40   *         return units;
41   *     }
42   *
43   *     // Can't be called getValue(), because Number is not a valid type
44   *     // in an MXBean, so the implied "value" property would be rejected.
45   *     public Number _getValue() {
46   *         return value;
47   *     }
48   *
49   *     public CompositeData toCompositeData(CompositeType ct) {
50   *         try {
51   *             {@code List<String> itemNames = new ArrayList<String>(ct.keySet());}
52   *             {@code List<String> itemDescriptions = new ArrayList<String>();}
53   *             {@code List<OpenType<?>> itemTypes = new ArrayList<OpenType<?>>();}
54   *             for (String item : itemNames) {
55   *                 itemDescriptions.add(ct.getDescription(item));
56   *                 itemTypes.add(ct.getType(item));
57   *             }
58   *             itemNames.add("value");
59   *             itemDescriptions.add("long or double value of the measure");
60   *             itemTypes.add((value instanceof Long) ? SimpleType.LONG :
61   *                           SimpleType.DOUBLE);
62   *             CompositeType xct =
63   *                 new CompositeType(ct.getTypeName(),
64   *                                   ct.getDescription(),
65   *                                   itemNames.toArray(new String[0]),
66   *                                   itemDescriptions.toArray(new String[0]),
67   *                                   itemTypes.toArray(new OpenType&lt;?&gt;[0]));
68   *             CompositeData cd =
69   *                 new CompositeDataSupport(xct,
70   *                                          new String[] {"units", "value"},
71   *                                          new Object[] {units, value});
72   *             assert ct.isValue(cd);  // check we've done it right
73   *             return cd;
74   *         } catch (Exception e) {
75   *             throw new RuntimeException(e);
76   *         }
77   *     }
78   * }
79   * </pre>
80   *
81   * <p>The {@code CompositeType} that will appear in the {@code openType} field
82   * of the {@link javax.management.Descriptor Descriptor} for an attribute or
83   * operation of this type will show only the {@code units} item, but the actual
84   * {@code CompositeData} that is generated will have both {@code units} and
85   * {@code value}.</p>
86   *
87   * @see javax.management.MXBean
88   *
89   * @since 1.6
90   */
91  public interface CompositeDataView {
92      /**
93       * <p>Return a {@code CompositeData} corresponding to the values in
94       * this object.  The returned value should usually be an instance of
95       * {@link CompositeDataSupport}, or a class that serializes as a
96       * {@code CompositeDataSupport} via a {@code writeReplace} method.
97       * Otherwise, a remote client that receives the object might not be
98       * able to reconstruct it.
99       *
100      * @param ct The expected {@code CompositeType} of the returned
101      * value.  If the returned value is {@code cd}, then
102      * {@code cd.getCompositeType().equals(ct)} should be true.
103      * Typically this will be because {@code cd} is a
104      * {@link CompositeDataSupport} constructed with {@code ct} as its
105      * {@code CompositeType}.
106      *
107      * @return the {@code CompositeData}.
108      */
109     public CompositeData   toCompositeData(CompositeType   ct);
110 }
111
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