/*
* Copyright (C) 2010 Google Inc.
*
* 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.google.gson.stream;
import java.io.Closeable;
import java.io.Flushable;
import java.io.IOException;
import java.io.Writer;
import static com.google.gson.stream.JsonScope.DANGLING_NAME;
import static com.google.gson.stream.JsonScope.EMPTY_ARRAY;
import static com.google.gson.stream.JsonScope.EMPTY_DOCUMENT;
import static com.google.gson.stream.JsonScope.EMPTY_OBJECT;
import static com.google.gson.stream.JsonScope.NONEMPTY_ARRAY;
import static com.google.gson.stream.JsonScope.NONEMPTY_DOCUMENT;
import static com.google.gson.stream.JsonScope.NONEMPTY_OBJECT;
/**
* 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 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
* }
* }
* ]}</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.setIndentSpaces(4);
* 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}.
*
* @author Jesse Wilson
* @since 1.6
*/
public class JsonWriter implements Closeable, Flushable {
/*
* 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)."
*
* We also escape '\u2028' and '\u2029', which JavaScript interprets as
* newline characters. This prevents eval() from failing with a syntax
* error. http://code.google.com/p/google-gson/issues/detail?id=341
*/
private static final String[] REPLACEMENT_CHARS;
private static final String[] HTML_SAFE_REPLACEMENT_CHARS;
static {
REPLACEMENT_CHARS = new String[128];
for (int i = 0; i <= 0x1f; i++) {
REPLACEMENT_CHARS[i] = String.format("\\u%04x", (int) i);
}
REPLACEMENT_CHARS['"'] = "\\\"";
REPLACEMENT_CHARS['\\'] = "\\\\";
REPLACEMENT_CHARS['\t'] = "\\t";
REPLACEMENT_CHARS['\b'] = "\\b";
REPLACEMENT_CHARS['\n'] = "\\n";
REPLACEMENT_CHARS['\r'] = "\\r";
REPLACEMENT_CHARS['\f'] = "\\f";
HTML_SAFE_REPLACEMENT_CHARS = REPLACEMENT_CHARS.clone();
HTML_SAFE_REPLACEMENT_CHARS['<'] = "\\u003c";
HTML_SAFE_REPLACEMENT_CHARS['>'] = "\\u003e";
HTML_SAFE_REPLACEMENT_CHARS['&'] = "\\u0026";
HTML_SAFE_REPLACEMENT_CHARS['='] = "\\u003d";
HTML_SAFE_REPLACEMENT_CHARS['\''] = "\\u0027";
}
/**
* The output data, containing at most one top-level array or object.
*/
private final Writer out;
private int[] stack = new int[32];
private int stackSize = 0;
{
push(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 = ":";
private boolean lenient;
private boolean htmlSafe;
private String deferredName;
private boolean serializeNulls = true;
/**
* 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 final void setIndent(String indent) {
if (indent.length() == 0) {
this.indent = null;
this.separator = ":";
} else {
this.indent = indent;
this.separator = ": ";
}
}
/**
* Configure this writer to relax its syntax rules. By default, this writer only emits
* well-formed JSON as specified by <a href="http://www.ietf.org/rfc/rfc4627.txt">RFC
* 4627</a>. Setting the writer to lenient permits the following:
* <ul>
* <li>Top-level values of any type. With strict writing, the top-level value must be an
* object or an array.
* <li>Numbers may be {@link Double#isNaN() NaNs} or {@link
* Double#isInfinite() infinities}.
* </ul>
*/
public final void setLenient(boolean lenient) {
this.lenient = lenient;
}
/**
* Returns true if this writer has relaxed syntax rules.
*/
public boolean isLenient() {
return lenient;
}
/**
* Configure this writer to emit JSON that's safe for direct inclusion in HTML and XML
* documents. This escapes the HTML characters {@code <}, {@code >},
* {@code &} and {@code =} before writing them to the stream. Without this setting, your
* XML/HTML encoder should replace these characters with the corresponding escape sequences.
*/
public final void setHtmlSafe(boolean htmlSafe) {
this.htmlSafe = htmlSafe;
}
/**
* Returns true if this writer writes JSON that's safe for inclusion in HTML and XML
* documents.
*/
public final boolean isHtmlSafe() {
return htmlSafe;
}
/**
* Sets whether object members are serialized when their value is null. This has no impact on
* array elements. The default is true.
*/
public final void setSerializeNulls(boolean serializeNulls) {
this.serializeNulls = serializeNulls;
}
/**
* Returns true if object members are serialized when their value is null. This has no impact
* on array elements. The default is true.
*/
public final boolean getSerializeNulls() {
return serializeNulls;
}
/**
* 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 {
writeDeferredName();
return open(EMPTY_ARRAY, "[");
}
/**
* Ends encoding the current array.
*
* @return this writer.
*/
public JsonWriter endArray() throws IOException {
return close(EMPTY_ARRAY, 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 {
writeDeferredName();
return open(EMPTY_OBJECT, "{");
}
/**
* Ends encoding the current object.
*
* @return this writer.
*/
public JsonWriter endObject() throws IOException {
return close(EMPTY_OBJECT, NONEMPTY_OBJECT, "}");
}
/**
* Enters a new scope by appending any necessary whitespace and the given bracket.
*/
private JsonWriter open(int empty, String openBracket) throws IOException {
beforeValue(true);
push(empty);
out.write(openBracket);
return this;
}
/**
* Closes the current scope by appending any necessary whitespace and the given bracket.
*/
private JsonWriter close(int empty, int nonempty, String closeBracket)
throws IOException {
int context = peek();
if (context != nonempty && context != empty) {
throw new IllegalStateException("Nesting problem.");
}
if (deferredName != null) {
throw new IllegalStateException("Dangling name: " + deferredName);
}
stackSize--;
if (context == nonempty) {
newline();
}
out.write(closeBracket);
return this;
}
private void push(int newTop) {
if (stackSize == stack.length) {
int[] newStack = new int[stackSize * 2];
System.arraycopy(stack, 0, newStack, 0, stackSize);
stack = newStack;
}
stack[stackSize++] = newTop;
}
/**
* Returns the value on the top of the stack.
*/
private int peek() {
if (stackSize == 0) {
throw new IllegalStateException("JsonWriter is closed.");
}
return stack[stackSize - 1];
}
/**
* Replace the value on the top of the stack with the given value.
*/
private void replaceTop(int topOfStack) {
stack[stackSize - 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");
}
if (deferredName != null) {
throw new IllegalStateException();
}
if (stackSize == 0) {
throw new IllegalStateException("JsonWriter is closed.");
}
deferredName = name;
return this;
}
private void writeDeferredName() throws IOException {
if (deferredName != null) {
beforeName();
string(deferredName);
deferredName = null;
}
}
/**
* 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();
}
writeDeferredName();
beforeValue(false);
string(value);
return this;
}
/**
* Encodes {@code null}.
*
* @return this writer.
*/
public JsonWriter nullValue() throws IOException {
if (deferredName != null) {
if (serializeNulls) {
writeDeferredName();
} else {
deferredName = null;
return this; // skip the name and the value
}
}
beforeValue(false);
out.write("null");
return this;
}
/**
* Encodes {@code value}.
*
* @return this writer.
*/
public JsonWriter value(boolean value) throws IOException {
writeDeferredName();
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);
}
writeDeferredName();
beforeValue(false);
out.append(Double.toString(value));
return this;
}
/**
* Encodes {@code value}.
*
* @return this writer.
*/
public JsonWriter value(long value) throws IOException {
writeDeferredName();
beforeValue(false);
out.write(Long.toString(value));
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(Number value) throws IOException {
if (value == null) {
return nullValue();
}
writeDeferredName();
String string = value.toString();
if (!lenient
&& (string.equals("-Infinity") || string.equals("Infinity") || string.equals("NaN"))) {
throw new IllegalArgumentException("Numeric values must be finite, but was " + value);
}
beforeValue(false);
out.append(string);
return this;
}
/**
* Ensures all buffered data is written to the underlying {@link Writer} and flushes that
* writer.
*/
public void flush() throws IOException {
if (stackSize == 0) {
throw new IllegalStateException("JsonWriter is closed.");
}
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();
int size = stackSize;
if (size > 1 || size == 1 && stack[size - 1] != NONEMPTY_DOCUMENT) {
throw new IOException("Incomplete document");
}
stackSize = 0;
}
private void string(String value) throws IOException {
String[] replacements = htmlSafe ? HTML_SAFE_REPLACEMENT_CHARS : REPLACEMENT_CHARS;
out.write("\"");
int last = 0;
int length = value.length();
for (int i = 0; i < length; i++) {
char c = value.charAt(i);
String replacement;
if (c < 128) {
replacement = replacements[c];
if (replacement == null) {
continue;
}
} else if (c == '\u2028') {
replacement = "\\u2028";
} else if (c == '\u2029') {
replacement = "\\u2029";
} else {
continue;
}
if (last < i) {
out.write(value, last, i - last);
}
out.write(replacement);
last = i + 1;
}
if (last < length) {
out.write(value, last, length - last);
}
out.write("\"");
}
private void newline() throws IOException {
if (indent == null) {
return;
}
out.write("\n");
for (int i = 1, size = stackSize; i < 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 {
int context = peek();
if (context == NONEMPTY_OBJECT) { // first in object
out.write(',');
} else if (context != EMPTY_OBJECT) { // not in an object!
throw new IllegalStateException("Nesting problem.");
}
newline();
replaceTop(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.
*/
@SuppressWarnings("fallthrough")
private void beforeValue(boolean root) throws IOException {
switch (peek()) {
case NONEMPTY_DOCUMENT:
if (!lenient) {
throw new IllegalStateException(
"JSON must have only one top-level value.");
}
// fall-through
case EMPTY_DOCUMENT: // first in document
if (!lenient && !root) {
throw new IllegalStateException(
"JSON must start with an array or an object.");
}
replaceTop(NONEMPTY_DOCUMENT);
break;
case EMPTY_ARRAY: // first in array
replaceTop(NONEMPTY_ARRAY);
newline();
break;
case NONEMPTY_ARRAY: // another in array
out.append(',');
newline();
break;
case DANGLING_NAME: // value for name
out.append(separator);
replaceTop(NONEMPTY_OBJECT);
break;
default:
throw new IllegalStateException("Nesting problem.");
}
}
}