1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<!--NewPage-->
<HTML>
<HEAD>
<!-- Generated by javadoc (build 1.6.0_65) on Thu Nov 20 01:11:54 PST 2014 -->
<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
<TITLE>
InstanceCreator (Gson 2.3.1 API)
</TITLE>
<META NAME="date" CONTENT="2014-11-20">
<LINK REL ="stylesheet" TYPE="text/css" HREF="../../../stylesheet.css" TITLE="Style">
<SCRIPT type="text/javascript">
function windowTitle()
{
if (location.href.indexOf('is-external=true') == -1) {
parent.document.title="InstanceCreator (Gson 2.3.1 API)";
}
}
</SCRIPT>
<NOSCRIPT>
</NOSCRIPT>
</HEAD>
<BODY BGCOLOR="white" onload="windowTitle();">
<HR>
<!-- ========= START OF TOP NAVBAR ======= -->
<A NAME="navbar_top"><!-- --></A>
<A HREF="#skip-navbar_top" title="Skip navigation links"></A>
<TABLE BORDER="0" WIDTH="100%" CELLPADDING="1" CELLSPACING="0" SUMMARY="">
<TR>
<TD COLSPAN=2 BGCOLOR="#EEEEFF" CLASS="NavBarCell1">
<A NAME="navbar_top_firstrow"><!-- --></A>
<TABLE BORDER="0" CELLPADDING="0" CELLSPACING="3" SUMMARY="">
<TR ALIGN="center" VALIGN="top">
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../overview-summary.html"><FONT CLASS="NavBarFont1"><B>Overview</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-summary.html"><FONT CLASS="NavBarFont1"><B>Package</B></FONT></A> </TD>
<TD BGCOLOR="#FFFFFF" CLASS="NavBarCell1Rev"> <FONT CLASS="NavBarFont1Rev"><B>Class</B></FONT> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="class-use/InstanceCreator.html"><FONT CLASS="NavBarFont1"><B>Use</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-tree.html"><FONT CLASS="NavBarFont1"><B>Tree</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../deprecated-list.html"><FONT CLASS="NavBarFont1"><B>Deprecated</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../index-all.html"><FONT CLASS="NavBarFont1"><B>Index</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../help-doc.html"><FONT CLASS="NavBarFont1"><B>Help</B></FONT></A> </TD>
</TR>
</TABLE>
</TD>
<TD ALIGN="right" VALIGN="top" ROWSPAN=3><EM>
</EM>
</TD>
</TR>
<TR>
<TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2">
<A HREF="../../../com/google/gson/GsonBuilder.html" title="class in com.google.gson"><B>PREV CLASS</B></A>
<A HREF="../../../com/google/gson/JsonArray.html" title="class in com.google.gson"><B>NEXT CLASS</B></A></FONT></TD>
<TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2">
<A HREF="../../../index.html?com/google/gson/InstanceCreator.html" target="_top"><B>FRAMES</B></A>
<A HREF="InstanceCreator.html" target="_top"><B>NO FRAMES</B></A>
<SCRIPT type="text/javascript">
<!--
if(window==top) {
document.writeln('<A HREF="../../../allclasses-noframe.html"><B>All Classes</B></A>');
}
//-->
</SCRIPT>
<NOSCRIPT>
<A HREF="../../../allclasses-noframe.html"><B>All Classes</B></A>
</NOSCRIPT>
</FONT></TD>
</TR>
<TR>
<TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">
SUMMARY: NESTED | FIELD | CONSTR | <A HREF="#method_summary">METHOD</A></FONT></TD>
<TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">
DETAIL: FIELD | CONSTR | <A HREF="#method_detail">METHOD</A></FONT></TD>
</TR>
</TABLE>
<A NAME="skip-navbar_top"></A>
<!-- ========= END OF TOP NAVBAR ========= -->
<HR>
<!-- ======== START OF CLASS DATA ======== -->
<H2>
<FONT SIZE="-1">
com.google.gson</FONT>
<BR>
Interface InstanceCreator<T></H2>
<DL>
<DT><DT><B>Type Parameters:</B><DD><CODE>T</CODE> - the type of object that will be created by this implementation.</DL>
<HR>
<DL>
<DT><PRE>public interface <B>InstanceCreator<T></B></DL>
</PRE>
<P>
This interface is implemented to create instances of a class that does not define a no-args
constructor. If you can modify the class, you should instead add a private, or public
no-args constructor. However, that is not possible for library classes, such as JDK classes, or
a third-party library that you do not have source-code of. In such cases, you should define an
instance creator for the class. Implementations of this interface should be registered with
<A HREF="../../../com/google/gson/GsonBuilder.html#registerTypeAdapter(java.lang.reflect.Type, java.lang.Object)"><CODE>GsonBuilder.registerTypeAdapter(Type, Object)</CODE></A> method before Gson will be able to use
them.
<p>Let us look at an example where defining an InstanceCreator might be useful. The
<code>Id</code> class defined below does not have a default no-args constructor.</p>
<pre>
public class Id<T> {
private final Class<T> clazz;
private final long value;
public Id(Class<T> clazz, long value) {
this.clazz = clazz;
this.value = value;
}
}
</pre>
<p>If Gson encounters an object of type <code>Id</code> during deserialization, it will throw an
exception. The easiest way to solve this problem will be to add a (public or private) no-args
constructor as follows:</p>
<pre>
private Id() {
this(Object.class, 0L);
}
</pre>
<p>However, let us assume that the developer does not have access to the source-code of the
<code>Id</code> class, or does not want to define a no-args constructor for it. The developer
can solve this problem by defining an <code>InstanceCreator</code> for <code>Id</code>:</p>
<pre>
class IdInstanceCreator implements InstanceCreator<Id> {
public Id createInstance(Type type) {
return new Id(Object.class, 0L);
}
}
</pre>
<p>Note that it does not matter what the fields of the created instance contain since Gson will
overwrite them with the deserialized values specified in Json. You should also ensure that a
<i>new</i> object is returned, not a common object since its fields will be overwritten.
The developer will need to register <code>IdInstanceCreator</code> with Gson as follows:</p>
<pre>
Gson gson = new GsonBuilder().registerTypeAdapter(Id.class, new IdInstanceCreator()).create();
</pre>
<P>
<P>
<DL>
<DT><B>Author:</B></DT>
<DD>Inderjeet Singh, Joel Leitch</DD>
</DL>
<HR>
<P>
<!-- ========== METHOD SUMMARY =========== -->
<A NAME="method_summary"><!-- --></A>
<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
<TH ALIGN="left" COLSPAN="2"><FONT SIZE="+2">
<B>Method Summary</B></FONT></TH>
</TR>
<TR BGCOLOR="white" CLASS="TableRowColor">
<TD ALIGN="right" VALIGN="top" WIDTH="1%"><FONT SIZE="-1">
<CODE> <A HREF="../../../com/google/gson/InstanceCreator.html" title="type parameter in InstanceCreator">T</A></CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../com/google/gson/InstanceCreator.html#createInstance(java.lang.reflect.Type)">createInstance</A></B>(<A HREF="http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/reflect/Type.html?is-external=true" title="class or interface in java.lang.reflect">Type</A> type)</CODE>
<BR>
Gson invokes this call-back method during deserialization to create an instance of the
specified type.</TD>
</TR>
</TABLE>
<P>
<!-- ============ METHOD DETAIL ========== -->
<A NAME="method_detail"><!-- --></A>
<TABLE BORDER="1" WIDTH="100%" CELLPADDING="3" CELLSPACING="0" SUMMARY="">
<TR BGCOLOR="#CCCCFF" CLASS="TableHeadingColor">
<TH ALIGN="left" COLSPAN="1"><FONT SIZE="+2">
<B>Method Detail</B></FONT></TH>
</TR>
</TABLE>
<A NAME="createInstance(java.lang.reflect.Type)"><!-- --></A><H3>
createInstance</H3>
<PRE>
<A HREF="../../../com/google/gson/InstanceCreator.html" title="type parameter in InstanceCreator">T</A> <B>createInstance</B>(<A HREF="http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/reflect/Type.html?is-external=true" title="class or interface in java.lang.reflect">Type</A> type)</PRE>
<DL>
<DD>Gson invokes this call-back method during deserialization to create an instance of the
specified type. The fields of the returned instance are overwritten with the data present
in the Json. Since the prior contents of the object are destroyed and overwritten, do not
return an instance that is useful elsewhere. In particular, do not return a common instance,
always use <code>new</code> to create a new instance.
<P>
<DD><DL>
<DT><B>Parameters:</B><DD><CODE>type</CODE> - the parameterized T represented as a <A HREF="http://docs.oracle.com/javase/1.5.0/docs/api/java/lang/reflect/Type.html?is-external=true" title="class or interface in java.lang.reflect"><CODE>Type</CODE></A>.
<DT><B>Returns:</B><DD>a default object instance of type T.</DL>
</DD>
</DL>
<!-- ========= END OF CLASS DATA ========= -->
<HR>
<!-- ======= START OF BOTTOM NAVBAR ====== -->
<A NAME="navbar_bottom"><!-- --></A>
<A HREF="#skip-navbar_bottom" title="Skip navigation links"></A>
<TABLE BORDER="0" WIDTH="100%" CELLPADDING="1" CELLSPACING="0" SUMMARY="">
<TR>
<TD COLSPAN=2 BGCOLOR="#EEEEFF" CLASS="NavBarCell1">
<A NAME="navbar_bottom_firstrow"><!-- --></A>
<TABLE BORDER="0" CELLPADDING="0" CELLSPACING="3" SUMMARY="">
<TR ALIGN="center" VALIGN="top">
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../overview-summary.html"><FONT CLASS="NavBarFont1"><B>Overview</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-summary.html"><FONT CLASS="NavBarFont1"><B>Package</B></FONT></A> </TD>
<TD BGCOLOR="#FFFFFF" CLASS="NavBarCell1Rev"> <FONT CLASS="NavBarFont1Rev"><B>Class</B></FONT> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="class-use/InstanceCreator.html"><FONT CLASS="NavBarFont1"><B>Use</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-tree.html"><FONT CLASS="NavBarFont1"><B>Tree</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../deprecated-list.html"><FONT CLASS="NavBarFont1"><B>Deprecated</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../index-all.html"><FONT CLASS="NavBarFont1"><B>Index</B></FONT></A> </TD>
<TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../help-doc.html"><FONT CLASS="NavBarFont1"><B>Help</B></FONT></A> </TD>
</TR>
</TABLE>
</TD>
<TD ALIGN="right" VALIGN="top" ROWSPAN=3><EM>
</EM>
</TD>
</TR>
<TR>
<TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2">
<A HREF="../../../com/google/gson/GsonBuilder.html" title="class in com.google.gson"><B>PREV CLASS</B></A>
<A HREF="../../../com/google/gson/JsonArray.html" title="class in com.google.gson"><B>NEXT CLASS</B></A></FONT></TD>
<TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2">
<A HREF="../../../index.html?com/google/gson/InstanceCreator.html" target="_top"><B>FRAMES</B></A>
<A HREF="InstanceCreator.html" target="_top"><B>NO FRAMES</B></A>
<SCRIPT type="text/javascript">
<!--
if(window==top) {
document.writeln('<A HREF="../../../allclasses-noframe.html"><B>All Classes</B></A>');
}
//-->
</SCRIPT>
<NOSCRIPT>
<A HREF="../../../allclasses-noframe.html"><B>All Classes</B></A>
</NOSCRIPT>
</FONT></TD>
</TR>
<TR>
<TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">
SUMMARY: NESTED | FIELD | CONSTR | <A HREF="#method_summary">METHOD</A></FONT></TD>
<TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">
DETAIL: FIELD | CONSTR | <A HREF="#method_detail">METHOD</A></FONT></TD>
</TR>
</TABLE>
<A NAME="skip-navbar_bottom"></A>
<!-- ======== END OF BOTTOM NAVBAR ======= -->
<HR>
Copyright © 2008–2014 <a href="http://www.google.com">Google, Inc.</a>. All rights reserved.
</BODY>
</HTML>
|
