Package com.google.gson.stream

Class JsonWriter

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

    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

    • Constructor Summary

      Constructors 
      Constructor 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 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​(java.lang.String value)
      Writes value directly to the writer without quoting or escaping.
      JsonWriter name​(java.lang.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​(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.
      JsonWriter value​(boolean value)
      Encodes value.
      JsonWriter value​(double value)
      Encodes value.
      JsonWriter value​(long value)
      Encodes value.
      JsonWriter value​(java.lang.Boolean value)
      Encodes value.
      JsonWriter value​(java.lang.Number value)
      Encodes value.
      JsonWriter value​(java.lang.String value)
      Encodes value.

      • Methods inherited from class java.lang.Object

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

    • 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

      • 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

      • 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.lang.AutoCloseable
        Specified by:
        close in interface java.io.Closeable
        Throws:
        java.io.IOException - if the JSON document is incomplete.