| /* |
| * Copyright (C) 2010 The Android Open Source Project |
| * |
| * Licensed under the Apache License, Version 2.0 (the "License"); |
| * you may not use this file except in compliance with the License. |
| * You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| |
| package com.android.json.stream; |
| |
| import java.io.Closeable; |
| import java.io.IOException; |
| import java.io.Writer; |
| import java.util.ArrayList; |
| import java.util.List; |
| |
| /** |
| * Writes a JSON (<a href="http://www.ietf.org/rfc/rfc4627.txt">RFC 4627</a>) |
| * 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. |
| * |
| * <h3>Encoding JSON</h3> |
| * 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: |
| * <ul> |
| * <li>To write <strong>arrays</strong>, 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()}. |
| * <li>To write <strong>objects</strong>, 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 the |
| * appropriate {@link #value} method or by nesting other objects or arrays. |
| * Finally close the object using {@link #endObject()}. |
| * </ul> |
| * |
| * <h3>Example</h3> |
| * Suppose we'd like to encode a stream of messages such as the following: <pre> {@code |
| * [ |
| * { |
| * "id": 912345678901, |
| * "text": "How do I write JSON on Android?", |
| * "geo": null, |
| * "user": { |
| * "name": "android_newb", |
| * "followers_count": 41 |
| * } |
| * }, |
| * { |
| * "id": 912345678902, |
| * "text": "@android_newb just use android.util.JsonWriter!", |
| * "geo": [50.454722, -104.606667], |
| * "user": { |
| * "name": "jesse", |
| * "followers_count": 2 |
| * } |
| * } |
| * ]}</pre> |
| * This code encodes the above structure: <pre> {@code |
| * 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(); |
| * }}</pre> |
| * |
| * <p>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}. |
| */ |
| public final class JsonWriter implements Closeable { |
| |
| /** The output data, containing at most one top-level array or object. */ |
| private final Writer out; |
| |
| private final List<JsonScope> stack = new ArrayList<JsonScope>(); |
| { |
| stack.add(JsonScope.EMPTY_DOCUMENT); |
| } |
| |
| /** |
| * A string containing a full set of spaces for a single level of |
| * indentation, or null for no pretty printing. |
| */ |
| private String indent; |
| |
| /** |
| * The name/value separator; either ":" or ": ". |
| */ |
| private String separator = ":"; |
| |
| /** |
| * Creates a new instance that writes a JSON-encoded stream to {@code out}. |
| * For best performance, ensure {@link Writer} is buffered; wrapping in |
| * {@link java.io.BufferedWriter BufferedWriter} if necessary. |
| */ |
| public JsonWriter(Writer out) { |
| if (out == null) { |
| throw new NullPointerException("out == null"); |
| } |
| this.out = out; |
| } |
| |
| /** |
| * Sets the indentation string to be repeated for each level of indentation |
| * in the encoded document. If {@code indent.isEmpty()} the encoded document |
| * will be compact. Otherwise the encoded document will be more |
| * human-readable. |
| * |
| * @param indent a string containing only whitespace. |
| */ |
| public void setIndent(String indent) { |
| if (indent.isEmpty()) { |
| this.indent = null; |
| this.separator = ":"; |
| } else { |
| this.indent = indent; |
| this.separator = ": "; |
| } |
| } |
| |
| /** |
| * Begins encoding a new array. Each call to this method must be paired with |
| * a call to {@link #endArray}. |
| * |
| * @return this writer. |
| */ |
| public JsonWriter beginArray() throws IOException { |
| return open(JsonScope.EMPTY_ARRAY, "["); |
| } |
| |
| /** |
| * Ends encoding the current array. |
| * |
| * @return this writer. |
| */ |
| public JsonWriter endArray() throws IOException { |
| return close(JsonScope.EMPTY_ARRAY, JsonScope.NONEMPTY_ARRAY, "]"); |
| } |
| |
| /** |
| * Begins encoding a new object. Each call to this method must be paired |
| * with a call to {@link #endObject}. |
| * |
| * @return this writer. |
| */ |
| public JsonWriter beginObject() throws IOException { |
| return open(JsonScope.EMPTY_OBJECT, "{"); |
| } |
| |
| /** |
| * Ends encoding the current object. |
| * |
| * @return this writer. |
| */ |
| public JsonWriter endObject() throws IOException { |
| return close(JsonScope.EMPTY_OBJECT, JsonScope.NONEMPTY_OBJECT, "}"); |
| } |
| |
| /** |
| * Enters a new scope by appending any necessary whitespace and the given |
| * bracket. |
| */ |
| private JsonWriter open(JsonScope empty, String openBracket) throws IOException { |
| beforeValue(true); |
| stack.add(empty); |
| out.write(openBracket); |
| return this; |
| } |
| |
| /** |
| * Closes the current scope by appending any necessary whitespace and the |
| * given bracket. |
| */ |
| private JsonWriter close(JsonScope empty, JsonScope nonempty, String closeBracket) |
| throws IOException { |
| JsonScope context = peek(); |
| if (context != nonempty && context != empty) { |
| throw new IllegalStateException("Nesting problem: " + stack); |
| } |
| |
| stack.remove(stack.size() - 1); |
| if (context == nonempty) { |
| newline(); |
| } |
| out.write(closeBracket); |
| return this; |
| } |
| |
| /** |
| * Returns the value on the top of the stack. |
| */ |
| private JsonScope peek() { |
| return stack.get(stack.size() - 1); |
| } |
| |
| /** |
| * Replace the value on the top of the stack with the given value. |
| */ |
| private void replaceTop(JsonScope topOfStack) { |
| stack.set(stack.size() - 1, topOfStack); |
| } |
| |
| /** |
| * Encodes the property name. |
| * |
| * @param name the name of the forthcoming value. May not be null. |
| * @return this writer. |
| */ |
| public JsonWriter name(String name) throws IOException { |
| if (name == null) { |
| throw new NullPointerException("name == null"); |
| } |
| beforeName(); |
| string(name); |
| return this; |
| } |
| |
| /** |
| * Encodes {@code value}. |
| * |
| * @param value the literal string value, or null to encode a null literal. |
| * @return this writer. |
| */ |
| public JsonWriter value(String value) throws IOException { |
| if (value == null) { |
| return nullValue(); |
| } |
| beforeValue(false); |
| string(value); |
| return this; |
| } |
| |
| /** |
| * Encodes {@code null}. |
| * |
| * @return this writer. |
| */ |
| public JsonWriter nullValue() throws IOException { |
| beforeValue(false); |
| out.write("null"); |
| return this; |
| } |
| |
| /** |
| * Encodes {@code value}. |
| * |
| * @return this writer. |
| */ |
| public JsonWriter value(boolean value) throws IOException { |
| beforeValue(false); |
| out.write(value ? "true" : "false"); |
| return this; |
| } |
| |
| /** |
| * Encodes {@code value}. |
| * |
| * @param value a finite value. May not be {@link Double#isNaN() NaNs} or |
| * {@link Double#isInfinite() infinities}. |
| * @return this writer. |
| */ |
| public JsonWriter value(double value) throws IOException { |
| if (Double.isNaN(value) || Double.isInfinite(value)) { |
| throw new IllegalArgumentException("Numeric values must be finite, but was " + value); |
| } |
| beforeValue(false); |
| out.append(Double.toString(value)); |
| return this; |
| } |
| |
| /** |
| * Encodes {@code value}. |
| * |
| * @return this writer. |
| */ |
| public JsonWriter value(long value) throws IOException { |
| beforeValue(false); |
| out.write(Long.toString(value)); |
| return this; |
| } |
| |
| /** |
| * Ensures all buffered data is written to the underlying {@link Writer} |
| * and flushes that writer. |
| */ |
| public void flush() throws IOException { |
| out.flush(); |
| } |
| |
| /** |
| * Flushes and closes this writer and the underlying {@link Writer}. |
| * |
| * @throws IOException if the JSON document is incomplete. |
| */ |
| public void close() throws IOException { |
| out.close(); |
| |
| if (peek() != JsonScope.NONEMPTY_DOCUMENT) { |
| throw new IOException("Incomplete document"); |
| } |
| } |
| |
| private void string(String value) throws IOException { |
| out.write("\""); |
| for (int i = 0, length = value.length(); i < length; i++) { |
| char c = value.charAt(i); |
| |
| /* |
| * From RFC 4627, "All Unicode characters may be placed within the |
| * quotation marks except for the characters that must be escaped: |
| * quotation mark, reverse solidus, and the control characters |
| * (U+0000 through U+001F)." |
| */ |
| switch (c) { |
| case '"': |
| case '\\': |
| case '/': |
| out.write('\\'); |
| out.write(c); |
| break; |
| |
| case '\t': |
| out.write("\\t"); |
| break; |
| |
| case '\b': |
| out.write("\\b"); |
| break; |
| |
| case '\n': |
| out.write("\\n"); |
| break; |
| |
| case '\r': |
| out.write("\\r"); |
| break; |
| |
| case '\f': |
| out.write("\\f"); |
| break; |
| |
| default: |
| if (c <= 0x1F) { |
| out.write(String.format("\\u%04x", (int) c)); |
| } else { |
| out.write(c); |
| } |
| break; |
| } |
| |
| } |
| out.write("\""); |
| } |
| |
| private void newline() throws IOException { |
| if (indent == null) { |
| return; |
| } |
| |
| out.write("\n"); |
| for (int i = 1; i < stack.size(); i++) { |
| out.write(indent); |
| } |
| } |
| |
| /** |
| * Inserts any necessary separators and whitespace before a name. Also |
| * adjusts the stack to expect the name's value. |
| */ |
| private void beforeName() throws IOException { |
| JsonScope context = peek(); |
| if (context == JsonScope.NONEMPTY_OBJECT) { // first in object |
| out.write(','); |
| } else if (context != JsonScope.EMPTY_OBJECT) { // not in an object! |
| throw new IllegalStateException("Nesting problem: " + stack); |
| } |
| newline(); |
| replaceTop(JsonScope.DANGLING_NAME); |
| } |
| |
| /** |
| * 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. |
| * |
| * @param root true if the value is a new array or object, the two values |
| * permitted as top-level elements. |
| */ |
| private void beforeValue(boolean root) throws IOException { |
| switch (peek()) { |
| case EMPTY_DOCUMENT: // first in document |
| if (!root) { |
| throw new IllegalStateException( |
| "JSON must start with an array or an object."); |
| } |
| replaceTop(JsonScope.NONEMPTY_DOCUMENT); |
| break; |
| |
| case EMPTY_ARRAY: // first in array |
| replaceTop(JsonScope.NONEMPTY_ARRAY); |
| newline(); |
| break; |
| |
| case NONEMPTY_ARRAY: // another in array |
| out.append(','); |
| newline(); |
| break; |
| |
| case DANGLING_NAME: // value for name |
| out.append(separator); |
| replaceTop(JsonScope.NONEMPTY_OBJECT); |
| break; |
| |
| case NONEMPTY_DOCUMENT: |
| throw new IllegalStateException( |
| "JSON must have only one top-level value."); |
| |
| default: |
| throw new IllegalStateException("Nesting problem: " + stack); |
| } |
| } |
| } |