JsonWriter (Gson 2.8.1 API)

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 7159) 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.setIndent("    ");
     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.

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

Method Summary

All Methods Instance Methods Concrete 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`	`jsonValue(String value)` Writes `value` directly to the writer without quoting or escaping.
`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(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 7159. 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
  - jsonValue
```
public JsonWriter jsonValue(String value)
                     throws IOException
```
    Writes value directly to the writer without quoting or escaping.
    
    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(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.

Class JsonWriter

Encoding JSON

Example

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Constructor Detail

JsonWriter

Method Detail

setIndent

setLenient

isLenient

setHtmlSafe

isHtmlSafe

setSerializeNulls

getSerializeNulls

beginArray

endArray

beginObject

endObject

name

value

jsonValue

nullValue

value

value

value

value

value

flush

close