1 /* 2 * Copyright (C) 2010 Google Inc. 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.gson.internal; 18 19 import com.google.gson.JsonElement; 20 import com.google.gson.JsonIOException; 21 import com.google.gson.JsonNull; 22 import com.google.gson.JsonParseException; 23 import com.google.gson.JsonSyntaxException; 24 import com.google.gson.internal.bind.TypeAdapters; 25 import com.google.gson.stream.JsonReader; 26 import com.google.gson.stream.JsonWriter; 27 import com.google.gson.stream.MalformedJsonException; 28 import java.io.EOFException; 29 import java.io.IOException; 30 import java.io.Writer; 31 import java.util.Objects; 32 33 /** 34 * Reads and writes GSON parse trees over streams. 35 */ 36 public final class Streams { Streams()37 private Streams() { 38 throw new UnsupportedOperationException(); 39 } 40 41 /** 42 * Takes a reader in any state and returns the next value as a JsonElement. 43 */ parse(JsonReader reader)44 public static JsonElement parse(JsonReader reader) throws JsonParseException { 45 boolean isEmpty = true; 46 try { 47 reader.peek(); 48 isEmpty = false; 49 return TypeAdapters.JSON_ELEMENT.read(reader); 50 } catch (EOFException e) { 51 /* 52 * For compatibility with JSON 1.5 and earlier, we return a JsonNull for 53 * empty documents instead of throwing. 54 */ 55 if (isEmpty) { 56 return JsonNull.INSTANCE; 57 } 58 // The stream ended prematurely so it is likely a syntax error. 59 throw new JsonSyntaxException(e); 60 } catch (MalformedJsonException e) { 61 throw new JsonSyntaxException(e); 62 } catch (IOException e) { 63 throw new JsonIOException(e); 64 } catch (NumberFormatException e) { 65 throw new JsonSyntaxException(e); 66 } 67 } 68 69 /** 70 * Writes the JSON element to the writer, recursively. 71 */ write(JsonElement element, JsonWriter writer)72 public static void write(JsonElement element, JsonWriter writer) throws IOException { 73 TypeAdapters.JSON_ELEMENT.write(writer, element); 74 } 75 writerForAppendable(Appendable appendable)76 public static Writer writerForAppendable(Appendable appendable) { 77 return appendable instanceof Writer ? (Writer) appendable : new AppendableWriter(appendable); 78 } 79 80 /** 81 * Adapts an {@link Appendable} so it can be passed anywhere a {@link Writer} 82 * is used. 83 */ 84 private static final class AppendableWriter extends Writer { 85 private final Appendable appendable; 86 private final CurrentWrite currentWrite = new CurrentWrite(); 87 AppendableWriter(Appendable appendable)88 AppendableWriter(Appendable appendable) { 89 this.appendable = appendable; 90 } 91 write(char[] chars, int offset, int length)92 @Override public void write(char[] chars, int offset, int length) throws IOException { 93 currentWrite.setChars(chars); 94 appendable.append(currentWrite, offset, offset + length); 95 } 96 flush()97 @Override public void flush() {} close()98 @Override public void close() {} 99 100 // Override these methods for better performance 101 // They would otherwise unnecessarily create Strings or char arrays 102 write(int i)103 @Override public void write(int i) throws IOException { 104 appendable.append((char) i); 105 } 106 write(String str, int off, int len)107 @Override public void write(String str, int off, int len) throws IOException { 108 // Appendable.append turns null -> "null", which is not desired here 109 Objects.requireNonNull(str); 110 appendable.append(str, off, off + len); 111 } 112 append(CharSequence csq)113 @Override public Writer append(CharSequence csq) throws IOException { 114 appendable.append(csq); 115 return this; 116 } 117 append(CharSequence csq, int start, int end)118 @Override public Writer append(CharSequence csq, int start, int end) throws IOException { 119 appendable.append(csq, start, end); 120 return this; 121 } 122 123 /** 124 * A mutable char sequence pointing at a single char[]. 125 */ 126 private static class CurrentWrite implements CharSequence { 127 private char[] chars; 128 private String cachedString; 129 setChars(char[] chars)130 void setChars(char[] chars) { 131 this.chars = chars; 132 this.cachedString = null; 133 } 134 length()135 @Override public int length() { 136 return chars.length; 137 } charAt(int i)138 @Override public char charAt(int i) { 139 return chars[i]; 140 } subSequence(int start, int end)141 @Override public CharSequence subSequence(int start, int end) { 142 return new String(chars, start, end - start); 143 } 144 145 // Must return string representation to satisfy toString() contract toString()146 @Override public String toString() { 147 if (cachedString == null) { 148 cachedString = new String(chars); 149 } 150 return cachedString; 151 } 152 } 153 } 154 } 155