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JAVA 자료구조 TypeAdapter (Gson 2.3.1 API) - Google Gson
2015.10.26 21:51
TypeAdapter (Gson 2.3.1 API) - Google Gson
com.google.gson
Class TypeAdapter<T>
java.lang.Object com.google.gson.TypeAdapter<T>
-
public abstract class TypeAdapter<T>
- extends Object
Converts Java objects to and from JSON.
Defining a type's JSON form
By default Gson converts application classes to JSON using its built-in type adapters. If Gson's default JSON conversion isn't appropriate for a type, extend this class to customize the conversion. Here's an example of a type adapter for an (X,Y) coordinate point:
public class PointAdapter extends TypeAdapter<Point> {
public Point read(JsonReader reader) throws IOException {
if (reader.peek() == JsonToken.NULL) {
reader.nextNull();
return null;
}
String xy = reader.nextString();
String[] parts = xy.split(",");
int x = Integer.parseInt(parts[0]);
int y = Integer.parseInt(parts[1]);
return new Point(x, y);
}
public void write(JsonWriter writer, Point value) throws IOException {
if (value == null) {
writer.nullValue();
return;
}
String xy = value.getX() + "," + value.getY();
writer.value(xy);
}
}
With this type adapter installed, Gson will convert Points
to JSON as strings like "5,8"
rather than objects like {"x":5,"y":8}
. In this case the type adapter binds a rich Java class to a compact JSON value.
The read()
method must read exactly one value and write()
must write exactly one value. For primitive types this is means readers should make exactly one call to nextBoolean()
, nextDouble()
, nextInt()
, nextLong()
, nextString()
or nextNull()
. Writers should make exactly one call to one of value()
or nullValue()
. For arrays, type adapters should start with a call to beginArray()
, convert all elements, and finish with a call to endArray()
. For objects, they should start with beginObject()
, convert the object, and finish with endObject()
. Failing to convert a value or converting too many values may cause the application to crash.
Type adapters should be prepared to read null from the stream and write it to the stream. Alternatively, they should use nullSafe()
method while registering the type adapter with Gson. If your Gson
instance has been configured to GsonBuilder.serializeNulls()
, these nulls will be written to the final document. Otherwise the value (and the corresponding name when writing to a JSON object) will be omitted automatically. In either case your type adapter must handle null.
To use a custom type adapter with Gson, you must register it with a GsonBuilder
:
GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(Point.class, new PointAdapter());
// if PointAdapter didn't check for nulls in its read/write methods, you should instead use
// builder.registerTypeAdapter(Point.class, new PointAdapter().nullSafe());
...
Gson gson = builder.create();
- Since:
- 2.1
Constructor Summary | |
---|---|
TypeAdapter() |
Method Summary | |
---|---|
T |
fromJson(Reader in) Converts the JSON document in in to a Java object. |
T |
fromJson(String json) Converts the JSON document in json to a Java object. |
T |
fromJsonTree(JsonElement jsonTree) Converts jsonTree to a Java object. |
TypeAdapter<T> |
nullSafe() This wrapper method is used to make a type adapter null tolerant. |
abstract T |
read(JsonReader in) Reads one JSON value (an array, object, string, number, boolean or null) and converts it to a Java object. |
String |
toJson(T value) Converts value to a JSON document. |
void |
toJson(Writer out, T value) Converts value to a JSON document and writes it to out . |
JsonElement |
toJsonTree(T value) Converts value to a JSON tree. |
abstract void |
write(JsonWriter out, T value) Writes one JSON value (an array, object, string, number, boolean or null) for value . |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Constructor Detail |
---|
TypeAdapter
public TypeAdapter()
Method Detail |
---|
write
public abstract void write(JsonWriter out, T value) throws IOException
- Writes one JSON value (an array, object, string, number, boolean or null) for
value
. -
- Parameters:
value
- the Java object to write. May be null.- Throws:
IOException
toJson
public final void toJson(Writer out, T value) throws IOException
- Converts
value
to a JSON document and writes it toout
. Unlike Gson's similartoJson
method, this write is strict. Create alenient
JsonWriter
and callwrite(com.google.gson.stream.JsonWriter, Object)
for lenient writing. -
- Parameters:
value
- the Java object to convert. May be null.- Throws:
IOException
- Since:
- 2.2
nullSafe
public final TypeAdapter<T> nullSafe()
- This wrapper method is used to make a type adapter null tolerant. In general, a type adapter is required to handle nulls in write and read methods. Here is how this is typically done:
Gson gson = new GsonBuilder().registerTypeAdapter(Foo.class, new TypeAdapter<Foo>() { public Foo read(JsonReader in) throws IOException { if (in.peek() == JsonToken.NULL) { in.nextNull(); return null; } // read a Foo from in and return it } public void write(JsonWriter out, Foo src) throws IOException { if (src == null) { out.nullValue(); return; } // write src as JSON to out } }).create();
Gson gson = new GsonBuilder().registerTypeAdapter(Foo.class, new TypeAdapter<Foo>() { public Foo read(JsonReader in) throws IOException { // read a Foo from in and return it } public void write(JsonWriter out, Foo src) throws IOException { // write src as JSON to out } }.nullSafe()).create();
-
toJson
public final String toJson(T value) throws IOException
- Converts
value
to a JSON document. Unlike Gson's similartoJson
method, this write is strict. Create alenient
JsonWriter
and callwrite(com.google.gson.stream.JsonWriter, Object)
for lenient writing. -
- Parameters:
value
- the Java object to convert. May be null.- Throws:
IOException
- Since:
- 2.2
toJsonTree
public final JsonElement toJsonTree(T value)
- Converts
value
to a JSON tree. -
- Parameters:
value
- the Java object to convert. May be null.- Returns:
- the converted JSON tree. May be
JsonNull
. - Since:
- 2.2
read
public abstract T read(JsonReader in) throws IOException
- Reads one JSON value (an array, object, string, number, boolean or null) and converts it to a Java object. Returns the converted object.
-
- Returns:
- the converted Java object. May be null.
- Throws:
IOException
fromJson
public final T fromJson(Reader in) throws IOException
- Converts the JSON document in
in
to a Java object. Unlike Gson's similarfromJson
method, this read is strict. Create alenient
JsonReader
and callread(JsonReader)
for lenient reading. -
- Returns:
- the converted Java object. May be null.
- Throws:
IOException
- Since:
- 2.2
fromJson
public final T fromJson(String json) throws IOException
- Converts the JSON document in
json
to a Java object. Unlike Gson's similarfromJson
method, this read is strict. Create alenient
JsonReader
and callread(JsonReader)
for lenient reading. -
- Returns:
- the converted Java object. May be null.
- Throws:
IOException
- Since:
- 2.2
fromJsonTree
public final T fromJsonTree(JsonElement jsonTree)
- Converts
jsonTree
to a Java object. -
- Parameters:
jsonTree
- the Java object to convert. May beJsonNull
.- Since:
- 2.2
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