Module com.google.gson
Package com.google.gson.stream

Class 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. Call methods on the writer as you walk the structure's contents, nesting arrays and objects as necessary:

    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 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:

      • 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.

      • 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. This might not be supported by all implementations, if not supported an UnsupportedOperationException is thrown.
        Parameters:
        value - the literal string value, or null to encode a null literal.
        Returns:
        this writer.
        Throws:
        UnsupportedOperationException - if this writer does not support writing raw JSON values.
        IOException
        Since:
        2.4