Examples of com.google.gson.stream.JsonWriter

com.google.gson.stream.JsonWriter

etf.org/rfc/rfc4627.txt">RFC 4627) 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 {@code 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 {@link #beginArray()}. Write each of the array's elements with the appropriate {@link #value}methods or by nesting other arrays and objects. Finally close the array using {@link #endArray()}.
To write objects, first call {@link #beginObject()}. Write each of the object's properties by alternating calls to {@link #name} with the property's value. Write property values with theappropriate {@link #value} method or by nesting other objects or arrays.Finally close the object using {@link #endObject()}.

Example

Suppose we'd like to encode a stream of messages such as the following:

  {@code [}{ "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:

    {@code}public void writeJsonStream(OutputStream out, List messages) throws IOException  JsonWriter writer = new JsonWriter(new OutputStreamWriter(out, "UTF-8")); writer.setIndentSpaces(4); writeMessagesArray(writer, messages); writer.close(); } public void writeMessagesArray(JsonWriter writer, List 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 doubles) throws IOException { writer.beginArray(); for (Double value : doubles) { writer.value(value); } writer.endArray(); }}

Each {@code 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 {@link IllegalStateException}. @author Jesse Wilson @since 1.6

  public void toJson(JsonElement jsonElement, Appendable writer) throws JsonIOException {
    try {
      if (generateNonExecutableJson) {
        writer.append(JSON_NON_EXECUTABLE_PREFIX);
      }
      JsonWriter jsonWriter = new JsonWriter(Streams.writerForAppendable(writer));
      if (prettyPrinting) {
        jsonWriter.setIndent("  ");
      }
      toJson(jsonElement, jsonWriter);
    } catch (IOException e) {
      throw new RuntimeException(e);
    }

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    return createJsonGenerator(new OutputStreamWriter(out, enc));
  }


  @Override
  public JsonGenerator createJsonGenerator(Writer writer) {
    return new GsonGenerator(this, new JsonWriter(writer));
  }

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  public void exportData(HttpServletResponse resp, Principal prin) throws IOException {


    resp.setContentType("application/json");


    // this writer puts things out onto the wire
    JsonWriter writer = new JsonWriter(resp.getWriter());
    writer.setIndent("  ");


    try {


          writer.beginObject();


      writer.name("exported-at");
      writer.value(dateFormat.format(new Date()));


      writer.name("exported-from");
      writer.value(config.getIssuer());


      writer.name("exported-by");
      writer.value(prin.getName());


      // delegate to the service to do the actual export
      dataService_1_1.exportData(writer);


      writer.endObject(); // end root
      writer.close();


    } catch (IOException e) {
      logger.error("Unable to export data", e);
    }
  }

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  protected void doPost(HttpServletRequest req, HttpServletResponse resp)
      throws ServletException, IOException {
    resp.setCharacterEncoding(ENCODING);
    resp.setContentType(CONTENT_TYPE_JSON);


    JsonWriter writer = new JsonWriter(resp.getWriter());
    String method = req.getParameter(WjrParamKey.KEY_METHOD);
    if (METHOD_LOAD_CONFIG.equals(method)) {
      writeConfig(writer, loadConfig(req));
    } else if (METHOD_LOAD_STORE.equals(method)) {
      writeStore(writer, loadStore());

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    public void writeTo(Object object, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, Object> httpHeaders, OutputStream entityStream) throws IOException,
            WebApplicationException {


        try (OutputStreamWriter writer = new OutputStreamWriter(entityStream, Charsets.UTF_8)) {
            try (JsonWriter jsonWriter = new JsonWriter(new BufferedWriter(writer))) {
                if (object instanceof GeneratedMessage) {
                    ProtobufJsonWriter.serialize((GeneratedMessage) object, jsonWriter);
                } else {
                    Iterable<? extends Message> iterable = (Iterable<? extends Message>) object;
                    jsonWriter.beginArray();
                    for (Message msg : iterable) {
                        ProtobufJsonWriter.serialize(msg, jsonWriter);
                    }
                    jsonWriter.endArray();
                }
            }
        }
    }

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  @Override public void processTrial(Trial trial) {
    if (!writer.isPresent()) {
      try {
        Files.createParentDirs(workFile);
        JsonWriter writer =
            new JsonWriter(new OutputStreamWriter(new FileOutputStream(workFile), Charsets.UTF_8));
        writer.setIndent("  ");  // always pretty print
        writer.beginArray();
        this.writer = Optional.of(writer);
      } catch (IOException e) {
        logger.log(SEVERE, String.format(
            "An error occured writing trial %s. Results in %s will be incomplete.", trial.id(),
            resultFile), e);
      }
    }
    if (writer.isPresent()) {
      gson.toJson(trial, Trial.class, writer.get());
    }
  }

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    Mockito.when(tokenRepository.getAllRefreshTokens()).thenReturn(allRefreshTokens);
    Mockito.when(sysScopeRepository.getAll()).thenReturn(new HashSet<SystemScope>());
        
    // do the data export
    StringWriter stringWriter = new StringWriter();
    JsonWriter writer = new JsonWriter(stringWriter);
    writer.beginObject();
    dataService.exportData(writer);
    writer.endObject();
    writer.close();
    
    // parse the output as a JSON object for testing
    JsonElement elem = new JsonParser().parse(stringWriter.toString());
    JsonObject root = elem.getAsJsonObject();

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    Mockito.when(tokenRepository.getAllAccessTokens()).thenReturn(allAccessTokens);
    Mockito.when(sysScopeRepository.getAll()).thenReturn(new HashSet<SystemScope>());
        
    // do the data export
    StringWriter stringWriter = new StringWriter();
    JsonWriter writer = new JsonWriter(stringWriter);
    writer.beginObject();
    dataService.exportData(writer);
    writer.endObject();
    writer.close();
    
    // parse the output as a JSON object for testing
    JsonElement elem = new JsonParser().parse(stringWriter.toString());
    JsonObject root = elem.getAsJsonObject();

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    Mockito.when(tokenRepository.getAllRefreshTokens()).thenReturn(new HashSet<OAuth2RefreshTokenEntity>());
    Mockito.when(sysScopeRepository.getAll()).thenReturn(new HashSet<SystemScope>());
    
    // do the data export
    StringWriter stringWriter = new StringWriter();
    JsonWriter writer = new JsonWriter(stringWriter);
    writer.beginObject();
    dataService.exportData(writer);
    writer.endObject();
    writer.close();
    
    // parse the output as a JSON object for testing
    JsonElement elem = new JsonParser().parse(stringWriter.toString());
    JsonObject root = elem.getAsJsonObject();

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    Mockito.when(tokenRepository.getAllRefreshTokens()).thenReturn(new HashSet<OAuth2RefreshTokenEntity>());
    Mockito.when(sysScopeRepository.getAll()).thenReturn(new HashSet<SystemScope>());
    
    // do the data export
    StringWriter stringWriter = new StringWriter();
    JsonWriter writer = new JsonWriter(stringWriter);
    writer.beginObject();
    dataService.exportData(writer);
    writer.endObject();
    writer.close();
    
    // parse the output as a JSON object for testing
    JsonElement elem = new JsonParser().parse(stringWriter.toString());
    JsonObject root = elem.getAsJsonObject();

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