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

Class 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. 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 Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method 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, char 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.
      private static boolean isTrustedNumberType​(java.lang.Class<? extends java.lang.Number> c)
      Returns whether the toString() of c can be trusted to return a valid JSON number.
      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, char 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​(double value)
      Encodes value.
      JsonWriter value​(float 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.
      private void writeDeferredName()  

      • Methods inherited from class java.lang.Object

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

    • Field Detail

      • VALID_JSON_NUMBER_PATTERN

        private static final java.util.regex.Pattern VALID_JSON_NUMBER_PATTERN

      • 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 JSON output destination

      • 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:
        • 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,
                        char 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,
                         char 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. 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:
        java.lang.UnsupportedOperationException - if this writer does not support writing raw JSON values.
        java.io.IOException
        Since:
        2.4

      • 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
        Since:
        2.7

      • value

        public JsonWriter value​(float value)
                 throws java.io.IOException
        Encodes value.
        Parameters:
        value - a finite value, or if lenient, also NaN or infinity.
        Returns:
        this writer.
        Throws:
        java.lang.IllegalArgumentException - if the value is NaN or Infinity and this writer is not lenient.
        java.io.IOException
        Since:
        2.9.1

      • value

        public JsonWriter value​(double value)
                 throws java.io.IOException
        Encodes value.
        Parameters:
        value - a finite value, or if lenient, also NaN or infinity.
        Returns:
        this writer.
        Throws:
        java.lang.IllegalArgumentException - if the value is NaN or Infinity and this writer is not lenient.
        java.io.IOException

      • value

        public JsonWriter value​(long value)
                 throws java.io.IOException
        Encodes value.
        Returns:
        this writer.
        Throws:
        java.io.IOException

      • isTrustedNumberType

        private static boolean isTrustedNumberType​(java.lang.Class<? extends java.lang.Number> c)
        Returns whether the toString() of c can be trusted to return a valid JSON number.

      • value

        public JsonWriter value​(java.lang.Number value)
                 throws java.io.IOException
        Encodes value. The value is written by directly writing the Object.toString() result to JSON. Implementations must make sure that the result represents a valid JSON number.
        Parameters:
        value - a finite value, or if lenient, also NaN or infinity.
        Returns:
        this writer.
        Throws:
        java.lang.IllegalArgumentException - if the value is NaN or Infinity and this writer is not lenient; or if the toString() result is not a valid JSON number.
        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.

      • 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