JsonWriter

java.lang.Object
- com.google.gson.stream.JsonWriter

All Implemented Interfaces:: java.io.Closeable, java.io.Flushable, java.lang.AutoCloseable

Direct Known Subclasses:: JsonTreeWriter

public class JsonWriter
extends java.lang.Object
implements java.io.Closeable, java.io.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

Field Summary

Fields
Modifier and Type	Field and Description
`private java.lang.String`	`deferredName`
`private static java.lang.String[]`	`HTML_SAFE_REPLACEMENT_CHARS`
`private boolean`	`htmlSafe`
`private java.lang.String`	`indent` A string containing a full set of spaces for a single level of indentation, or null for no pretty printing.
`private boolean`	`lenient`
`private java.io.Writer`	`out` The output data, containing at most one top-level array or object.
`private static java.lang.String[]`	`REPLACEMENT_CHARS`
`private java.lang.String`	`separator` The name/value separator; either ":" or ": ".
`private boolean`	`serializeNulls`
`private int[]`	`stack`
`private int`	`stackSize`

Constructor Summary

Constructors
Constructor and Description

JsonWriter(java.io.Writer out)
Creates a new instance that writes a JSON-encoded stream to out.

Constructors
Constructor and Description
`JsonWriter(java.io.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
`private void`	`beforeName()` Inserts any necessary separators and whitespace before a name.
`private void`	`beforeValue()` Inserts any necessary separators and whitespace before a literal value, inline array, or inline object.
`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`.
`private JsonWriter`	`close(int empty, int nonempty, java.lang.String closeBracket)` Closes the current scope by appending any necessary whitespace and the given bracket.
`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(java.lang.String value)` Writes `value` directly to the writer without quoting or escaping.
`JsonWriter`	`name(java.lang.String name)` Encodes the property name.
`private void`	`newline()`
`JsonWriter`	`nullValue()` Encodes `null`.
`private JsonWriter`	`open(int empty, java.lang.String openBracket)` Enters a new scope by appending any necessary whitespace and the given bracket.
`private int`	`peek()` Returns the value on the top of the stack.
`private void`	`push(int newTop)`
`private void`	`replaceTop(int topOfStack)` Replace the value on the top of the stack with the given value.
`void`	`setHtmlSafe(boolean htmlSafe)` Configure this writer to emit JSON that's safe for direct inclusion in HTML and XML documents.
`void`	`setIndent(java.lang.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.
`private void`	`string(java.lang.String value)`
`JsonWriter`	`value(boolean value)` Encodes `value`.
`JsonWriter`	`value(java.lang.Boolean value)` Encodes `value`.
`JsonWriter`	`value(double value)` Encodes `value`.
`JsonWriter`	`value(long value)` Encodes `value`.
`JsonWriter`	`value(java.lang.Number value)` Encodes `value`.
`JsonWriter`	`value(java.lang.String value)` Encodes `value`.
`private void`	`writeDeferredName()`

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - REPLACEMENT_CHARS
```
private static final java.lang.String[] REPLACEMENT_CHARS
```
  - HTML_SAFE_REPLACEMENT_CHARS
```
private static final java.lang.String[] HTML_SAFE_REPLACEMENT_CHARS
```
  - out
```
private final java.io.Writer out
```
    The output data, containing at most one top-level array or object.
  - stack
```
private int[] stack
```
  - stackSize
```
private int stackSize
```
  - indent
```
private java.lang.String indent
```
    A string containing a full set of spaces for a single level of indentation, or null for no pretty printing.
  - separator
```
private java.lang.String separator
```
    The name/value separator; either ":" or ": ".
  - lenient
```
private boolean lenient
```
  - htmlSafe
```
private boolean htmlSafe
```
  - deferredName
```
private java.lang.String deferredName
```
  - serializeNulls
```
private boolean serializeNulls
```
- Constructor Detail
  - JsonWriter
```
public JsonWriter(java.io.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(java.lang.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 java.io.IOException
```
    Begins encoding a new array. Each call to this method must be paired with a call to endArray().
    
    Returns:
    
    this writer.
    
    Throws:
    
    java.io.IOException
  - endArray
```
public JsonWriter endArray()
                    throws java.io.IOException
```
    Ends encoding the current array.
    
    Returns:
    
    this writer.
    
    Throws:
    
    java.io.IOException
  - beginObject
```
public JsonWriter beginObject()
                       throws java.io.IOException
```
    Begins encoding a new object. Each call to this method must be paired with a call to endObject().
    
    Returns:
    
    this writer.
    
    Throws:
    
    java.io.IOException
  - endObject
```
public JsonWriter endObject()
                     throws java.io.IOException
```
    Ends encoding the current object.
    
    Returns:
    
    this writer.
    
    Throws:
    
    java.io.IOException
  - open
```
private JsonWriter open(int empty,
                        java.lang.String openBracket)
                 throws java.io.IOException
```
    Enters a new scope by appending any necessary whitespace and the given bracket.
    
    Throws:
    
    java.io.IOException
  - close
```
private JsonWriter close(int empty,
                         int nonempty,
                         java.lang.String closeBracket)
                  throws java.io.IOException
```
    Closes the current scope by appending any necessary whitespace and the given bracket.
    
    Throws:
    
    java.io.IOException
  - push
```
private void push(int newTop)
```
  - peek
```
private int peek()
```
    Returns the value on the top of the stack.
  - replaceTop
```
private void replaceTop(int topOfStack)
```
    Replace the value on the top of the stack with the given value.
  - name
```
public JsonWriter name(java.lang.String name)
                throws java.io.IOException
```
    Encodes the property name.
    
    Parameters:
    
    name - the name of the forthcoming value. May not be null.
    
    Returns:
    
    this writer.
    
    Throws:
    
    java.io.IOException
  - writeDeferredName
```
private void writeDeferredName()
                        throws java.io.IOException
```
    Throws:
    
    java.io.IOException
  - value
```
public JsonWriter value(java.lang.String value)
                 throws java.io.IOException
```
    Encodes value.
    
    Parameters:
    
    value - the literal string value, or null to encode a null literal.
    
    Returns:
    
    this writer.
    
    Throws:
    
    java.io.IOException
  - jsonValue
```
public JsonWriter jsonValue(java.lang.String value)
                     throws java.io.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:
    
    java.io.IOException
  - nullValue
```
public JsonWriter nullValue()
                     throws java.io.IOException
```
    Encodes null.
    
    Returns:
    
    this writer.
    
    Throws:
    
    java.io.IOException
  - value
```
public JsonWriter value(boolean value)
                 throws java.io.IOException
```
    Encodes value.
    
    Returns:
    
    this writer.
    
    Throws:
    
    java.io.IOException
  - value
```
public JsonWriter value(java.lang.Boolean value)
                 throws java.io.IOException
```
    Encodes value.
    
    Returns:
    
    this writer.
    
    Throws:
    
    java.io.IOException
  - value
```
public JsonWriter value(double value)
                 throws java.io.IOException
```
    Encodes value.
    
    Parameters:
    
    value - a finite value. May not be NaNs or infinities.
    
    Returns:
    
    this writer.
    
    Throws:
    
    java.io.IOException
  - value
```
public JsonWriter value(long value)
                 throws java.io.IOException
```
    Encodes value.
    
    Returns:
    
    this writer.
    
    Throws:
    
    java.io.IOException
  - value
```
public JsonWriter value(java.lang.Number value)
                 throws java.io.IOException
```
    Encodes value.
    
    Parameters:
    
    value - a finite value. May not be NaNs or infinities.
    
    Returns:
    
    this writer.
    
    Throws:
    
    java.io.IOException
  - flush
```
public void flush()
           throws java.io.IOException
```
    Ensures all buffered data is written to the underlying Writer and flushes that writer.
    
    Specified by:
    
    flush in interface java.io.Flushable
    
    Throws:
    
    java.io.IOException
  - close
```
public void close()
           throws java.io.IOException
```
    Flushes and closes this writer and the underlying Writer.
    
    Specified by:
    
    close in interface java.io.Closeable
    
    Specified by:
    
    close in interface java.lang.AutoCloseable
    
    Throws:
    
    java.io.IOException - if the JSON document is incomplete.
  - string
```
private void string(java.lang.String value)
             throws java.io.IOException
```
    Throws:
    
    java.io.IOException
  - newline
```
private void newline()
              throws java.io.IOException
```
    Throws:
    
    java.io.IOException
  - beforeName
```
private void beforeName()
                 throws java.io.IOException
```
    Inserts any necessary separators and whitespace before a name. Also adjusts the stack to expect the name's value.
    
    Throws:
    
    java.io.IOException
  - beforeValue
```
private void beforeValue()
                  throws java.io.IOException
```
    Inserts any necessary separators and whitespace before a literal value, inline array, or inline object. Also adjusts the stack to expect either a closing bracket or another element.
    
    Throws:
    
    java.io.IOException

Class JsonWriter

Encoding JSON

Example

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

REPLACEMENT_CHARS

HTML_SAFE_REPLACEMENT_CHARS

out

stack

stackSize

indent

separator

lenient

htmlSafe

deferredName

serializeNulls

Constructor Detail

JsonWriter

Method Detail

setIndent

setLenient

isLenient

setHtmlSafe

isHtmlSafe

setSerializeNulls

getSerializeNulls

beginArray

endArray

beginObject

endObject

open

close

push

peek

replaceTop

name

writeDeferredName

value

jsonValue

nullValue

value

value

value

value

value

flush

close

string

newline

beforeName

beforeValue