com.google.gson.stream

Class JsonWriter

java.lang.Object

com.google.gson.stream.JsonWriter

All Implemented Interfaces:

Closeable, Flushable, AutoCloseable

public class JsonWriter
extends Object
implements Closeable, Flushable

Writes a JSON (RFC 4627) encoded value to a stream, one token at a time. The stream includes both literal values (strings, numbers, booleans and nulls) as well as the begin and end delimiters of objects and arrays.

Encoding JSON

To encode your data as JSON, create a new JsonWriter. Each JSON document must contain one top-level array or object. Call methods on the writer as you walk the structure's contents, nesting arrays and objects as necessary:

• To write arrays, first call beginArray(). Write each of the array's elements with the appropriate value(java.lang.String) methods or by nesting other arrays and objects. Finally close the array using endArray().
• To write objects, first call beginObject(). Write each of the object's properties by alternating calls to name(java.lang.String) with the property's value. Write property values with the appropriate value(java.lang.String) method or by nesting other objects or arrays. Finally close the object using endObject().

Example

Suppose we'd like to encode a stream of messages such as the following:

 [
   {
     "id": 912345678901,
     "text": "How do I stream JSON in Java?",
     "geo": null,
     "user": {
       "name": "json_newb",
       "followers_count": 41
      }
   },
   {
     "id": 912345678902,
     "text": "@json_newb just use JsonWriter!",
     "geo": [50.454722, -104.606667],
     "user": {
       "name": "jesse",
       "followers_count": 2
     }
   }
 ]

This code encodes the above structure:

   public void writeJsonStream(OutputStream out, List<Message> messages) throws IOException {
     JsonWriter writer = new JsonWriter(new OutputStreamWriter(out, "UTF-8"));
     writer.setIndentSpaces(4);
     writeMessagesArray(writer, messages);
     writer.close();
   }

   public void writeMessagesArray(JsonWriter writer, List<Message> messages) throws IOException {
     writer.beginArray();
     for (Message message : messages) {
       writeMessage(writer, message);
     }
     writer.endArray();
   }

   public void writeMessage(JsonWriter writer, Message message) throws IOException {
     writer.beginObject();
     writer.name("id").value(message.getId());
     writer.name("text").value(message.getText());
     if (message.getGeo() != null) {
       writer.name("geo");
       writeDoublesArray(writer, message.getGeo());
     } else {
       writer.name("geo").nullValue();
     }
     writer.name("user");
     writeUser(writer, message.getUser());
     writer.endObject();
   }

   public void writeUser(JsonWriter writer, User user) throws IOException {
     writer.beginObject();
     writer.name("name").value(user.getName());
     writer.name("followers_count").value(user.getFollowersCount());
     writer.endObject();
   }

   public void writeDoublesArray(JsonWriter writer, List<Double> doubles) throws IOException {
     writer.beginArray();
     for (Double value : doubles) {
       writer.value(value);
     }
     writer.endArray();
   }

Each JsonWriter may be used to write a single JSON stream. Instances of this class are not thread safe. Calls that would result in a malformed JSON string will fail with an IllegalStateException.

Since:

1.6

Author:

Jesse Wilson

Constructor Summary

Constructors

Constructor and Description
JsonWriter(Writer out) Creates a new instance that writes a JSON-encoded stream to out.

Method Summary

Methods

Modifier and Type	Method and Description
JsonWriter	beginArray() Begins encoding a new array.
JsonWriter	beginObject() Begins encoding a new object.
void	close() Flushes and closes this writer and the underlying Writer.
JsonWriter	endArray() Ends encoding the current array.
JsonWriter	endObject() Ends encoding the current object.
void	flush() Ensures all buffered data is written to the underlying Writer and flushes that writer.
boolean	getSerializeNulls() Returns true if object members are serialized when their value is null.
boolean	isHtmlSafe() Returns true if this writer writes JSON that's safe for inclusion in HTML and XML documents.
boolean	isLenient() Returns true if this writer has relaxed syntax rules.
JsonWriter	name(String name) Encodes the property name.
JsonWriter	nullValue() Encodes null.
void	setHtmlSafe(boolean htmlSafe) Configure this writer to emit JSON that's safe for direct inclusion in HTML and XML documents.
void	setIndent(String indent) Sets the indentation string to be repeated for each level of indentation in the encoded document.
void	setLenient(boolean lenient) Configure this writer to relax its syntax rules.
void	setSerializeNulls(boolean serializeNulls) Sets whether object members are serialized when their value is null.
JsonWriter	value(boolean value) Encodes value.
JsonWriter	value(double value) Encodes value.
JsonWriter	value(long value) Encodes value.
JsonWriter	value(Number value) Encodes value.
JsonWriter	value(String value) Encodes value.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

JsonWriter

public JsonWriter(Writer out)

Creates a new instance that writes a JSON-encoded stream to out. For best performance, ensure Writer is buffered; wrapping in BufferedWriter if necessary.

Method Detail

setIndent

public final void setIndent(String indent)

Sets the indentation string to be repeated for each level of indentation in the encoded document. If indent.isEmpty() the encoded document will be compact. Otherwise the encoded document will be more human-readable.

Parameters:

indent - a string containing only whitespace.

setLenient

public final void setLenient(boolean lenient)

Configure this writer to relax its syntax rules. By default, this writer only emits well-formed JSON as specified by RFC 4627. Setting the writer to lenient permits the following:

• Top-level values of any type. With strict writing, the top-level value must be an object or an array.
• Numbers may be NaNs or infinities.

isLenient

public boolean isLenient()

Returns true if this writer has relaxed syntax rules.

setHtmlSafe

public final void setHtmlSafe(boolean htmlSafe)

Configure this writer to emit JSON that's safe for direct inclusion in HTML and XML documents. This escapes the HTML characters <, >, & and = before writing them to the stream. Without this setting, your XML/HTML encoder should replace these characters with the corresponding escape sequences.

isHtmlSafe

public final boolean isHtmlSafe()

Returns true if this writer writes JSON that's safe for inclusion in HTML and XML documents.

setSerializeNulls

public final void setSerializeNulls(boolean serializeNulls)

Sets whether object members are serialized when their value is null. This has no impact on array elements. The default is true.

getSerializeNulls

public final boolean getSerializeNulls()

Returns true if object members are serialized when their value is null. This has no impact on array elements. The default is true.

beginArray

public JsonWriter beginArray()
                      throws IOException

Begins encoding a new array. Each call to this method must be paired with a call to endArray().

Returns:

this writer.

Throws:

IOException

endArray

public JsonWriter endArray()
                    throws IOException

Ends encoding the current array.

Returns:

this writer.

Throws:

IOException

beginObject

public JsonWriter beginObject()
                       throws IOException

Begins encoding a new object. Each call to this method must be paired with a call to endObject().

Returns:

this writer.

Throws:

IOException

endObject

public JsonWriter endObject()
                     throws IOException

Ends encoding the current object.

Returns:

this writer.

Throws:

IOException

name

public JsonWriter name(String name)
                throws IOException

Encodes the property name.

Parameters:

name - the name of the forthcoming value. May not be null.

Returns:

this writer.

Throws:

IOException

value

public JsonWriter value(String value)
                 throws IOException

Encodes value.

Parameters:

value - the literal string value, or null to encode a null literal.

Returns:

this writer.

Throws:

IOException

nullValue

public JsonWriter nullValue()
                     throws IOException

Encodes null.

Returns:

this writer.

Throws:

IOException

value

public JsonWriter value(boolean value)
                 throws IOException

Encodes value.

Returns:

this writer.

Throws:

IOException

value

public JsonWriter value(double value)
                 throws IOException

Encodes value.

Parameters:

value - a finite value. May not be NaNs or infinities.

Returns:

this writer.

Throws:

IOException

value

public JsonWriter value(long value)
                 throws IOException

Encodes value.

Returns:

this writer.

Throws:

IOException

value

public JsonWriter value(Number value)
                 throws IOException

Encodes value.

Parameters:

value - a finite value. May not be NaNs or infinities.

Returns:

this writer.

Throws:

IOException

flush

public void flush()
           throws IOException

Ensures all buffered data is written to the underlying Writer and flushes that writer.

Specified by:

flush in interface Flushable

Throws:

IOException

close

public void close()
           throws IOException

Flushes and closes this writer and the underlying Writer.

Specified by:

close in interface Closeable

Specified by:

close in interface AutoCloseable

Throws:

IOException - if the JSON document is incomplete.