Git 链接
Fastjson是一个Java语言编写的高性能功能完善的JSON库。它采用一种“假定有序快速匹配”的算法，把JSON Parse的性能提升到极致，是目前Java语言中最快的JSON库。Fastjson接口简单易用，已经被广泛使用在缓存序列化、协议交互、Web输出、Android客户端等多种应用场景。
git：https://github.com/alibaba/fastjson
Samples：https://github.com/alibaba/fastjson/wiki/Samples-DataBind
测试代码
@Test
public void test() {
User user = new User(0L, "json");
String jsonString = JSON.toJSONString(user);
System.out.println(jsonString);
User parseUser = JSON.parseObject(jsonString, User.class);
System.out.println(parseUser);
}
public class User {
private Longid;
private String name;
public User(long id, String name) {
this.id = id;
this.name = name;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}@Override
public String toString() {
return "User [id=" + id + ", name=" + name + "]";
}
}
输出：
{"id":0,"name":"json"}
User [id=0, name=json]
序列化、反序列化流程 序列化流程 根据对象的实例，获取对象的类，判断出实现 ObjectSerializer 接口的类，调用接口的方法 write，将对象实例转化成 String。
反序列化流程 根据输入的 Class
序列化源码分析 最终会调用到函数：
public static String toJSONString(Object object, //
SerializeConfig config, //
SerializeFilter[] filters, //
String dateFormat, //
int defaultFeatures, //
SerializerFeature... features) {
// out 对象保存解析对象的结果，最终会转换成 string（return out.toString();
）
SerializeWriter out = new SerializeWriter(null, defaultFeatures, features);
try {
// 解析对象的类
JSONSerializer serializer = new JSONSerializer(out, config);
if (dateFormat != null && dateFormat.length() != 0) {
serializer.setDateFormat(dateFormat);
serializer.config(SerializerFeature.WriteDateUseDateFormat, true);
}
if (filters != null) {
for (SerializeFilter filter : filters) {
serializer.addFilter(filter);
}
}
// 将对象 object 解析成 string，保存在内部的 out 中
serializer.write(object);
return out.toString();
} finally {
out.close();
}
}
其中
write 方法如下：public final void write(Object object) {
if (object == null) {
out.writeNull();
return;
}
Class clazz = object.getClass();
/**
* 获取到对应的解析类，所有的类都实现了接口 ObjectSerializer
*
* 如果是 bool，会定位到 BooleanCodec 类
* 如果是 bool[]，会定位到 PrimitiveArraySerializer 类
*/
ObjectSerializer writer = getObjectWriter(clazz);
try {
// 调用 write 方法，把对应的域，写入 out 对象中！
writer.write(this, object, null, null, 0);
} catch (IOException e) {
throw new JSONException(e.getMessage(), e);
}
}
在测试用例中，使用的是类
JavaBeanSerializer，因为要序列化的是自定义的 JavaBean 类 User。SerializeConfig
其中 put 函数是将键值对放入 IdentityHashMap
public SerializeConfig(int tableSize, boolean fieldBase) {
this.fieldBased = fieldBase;
serializers = new IdentityHashMap(tableSize);
try {
if (asm) {
asmFactory = new ASMSerializerFactory();
}
} catch (Throwable eror) {
asm = false;
}
put(Boolean.class, BooleanCodec.instance);
put(Character.class, CharacterCodec.instance);
put(Byte.class, IntegerCodec.instance);
put(Short.class, IntegerCodec.instance);
put(Integer.class, IntegerCodec.instance);
put(Long.class, LongCodec.instance);
put(Float.class, FloatCodec.instance);
put(Double.class, DoubleSerializer.instance);
put(BigDecimal.class, BigDecimalCodec.instance);
put(BigInteger.class, BigIntegerCodec.instance);
put(String.class, StringCodec.instance);
put(byte[].class, PrimitiveArraySerializer.instance);
put(short[].class, PrimitiveArraySerializer.instance);
put(int[].class, PrimitiveArraySerializer.instance);
put(long[].class, PrimitiveArraySerializer.instance);
put(float[].class, PrimitiveArraySerializer.instance);
put(double[].class, PrimitiveArraySerializer.instance);
put(boolean[].class, PrimitiveArraySerializer.instance);
put(char[].class, PrimitiveArraySerializer.instance);
put(Object[].class, ObjectArrayCodec.instance);
put(Class.class, MiscCodec.instance);
// 省略……
put(LinkedList.class, CollectionCodec.instance);
}
分析其中的代码：
put(Boolean.class, BooleanCodec.instance);
类 BooleanCodec 继承了接口 ObjectSerializer, ObjectDeserializer，两个接口：
public interface ObjectSerializer {/**
* fastjson invokes this call-back method during serialization when it encounters a field of the
* specified type.
* @param serializer
* @param object src the object that needs to be converted to Json.
* @param fieldName parent object field name
* @param fieldType parent object field type
* @param features parent object field serializer features
* @throws IOException
*/
void write(JSONSerializer serializer, //
Object object, //
Object fieldName, //
Type fieldType, //
int features) throws IOException;
}
public interface ObjectDeserializer {
/**
* fastjson invokes this call-back method during deserialization when it encounters a field of the
* specified type.
* In the implementation of this call-back method, you should consider invoking
* {@link JSON#parseObject(String, Type, Feature[])} method to create objects
* for any non-trivial field of the returned object.
*
* @param parser context DefaultJSONParser being deserialized
* @param type The type of the Object to deserialize to
* @param fieldName parent object field name
* @return a deserialized object of the specified type which is a subclass of {@code T}
*/
T deserialze(DefaultJSONParser parser, Type type, Object fieldName);
int getFastMatchToken();
}
BooleanCodec 的 write 实现如下，其中参数 serializer 中包含实例为 out 的 SerializeWriter 对象，out 最终转换成输出的 string；
public void write(JSONSerializer serializer, Object object, Object fieldName, Type fieldType, int features) throws IOException {
SerializeWriter out = serializer.out;
Boolean value = https://www.it610.com/article/(Boolean) object;
if (value == null) {
out.writeNull(SerializerFeature.WriteNullBooleanAsFalse);
return;
}
if (value.booleanValue()) {
out.write("true");
} else {
out.write("false");
}
}
BooleanCodec 的 deserialze 实现如下，如果 lexer.token() 是 true、1等，就会返回true；类 JSONToken 中有对各种字符的定义。
@SuppressWarnings("unchecked")
public T deserialze(DefaultJSONParser parser, Type clazz, Object fieldName) {
final JSONLexer lexer = parser.lexer;
Boolean boolObj;
try {
if (lexer.token() == JSONToken.TRUE) {
lexer.nextToken(JSONToken.COMMA);
boolObj = Boolean.TRUE;
} else if (lexer.token() == JSONToken.FALSE) {
lexer.nextToken(JSONToken.COMMA);
boolObj = Boolean.FALSE;
} else if (lexer.token() == JSONToken.LITERAL_INT) {
int intValue = https://www.it610.com/article/lexer.intValue();
lexer.nextToken(JSONToken.COMMA);
if (intValue == 1) {
boolObj = Boolean.TRUE;
} else {
boolObj = Boolean.FALSE;
}
} else {
Object value = parser.parse();
if (value == null) {
return null;
}
boolObj = TypeUtils.castToBoolean(value);
}
} catch (Exception ex) {
throw new JSONException("parseBoolean error, field : " + fieldName, ex);
}
if (clazz == AtomicBoolean.class) {
return (T) new AtomicBoolean(boolObj.booleanValue());
}
return (T) boolObj;
}
反序列化 在反序列化string到对象时，会调用下面的函数。其中最重要的是第25行代码，将输入的input字符串转换成对应的class类型。
@SuppressWarnings("unchecked")
public static T parseObject(String input, Type clazz, ParserConfig config, ParseProcess processor,
int featureValues, Feature... features) {
if (input == null) {
return null;
}
if (features != null) {
for (Feature feature : features) {
featureValues |= feature.mask;
}
}
DefaultJSONParser parser = new DefaultJSONParser(input, config, featureValues);
if (processor != null) {
if (processor instanceof ExtraTypeProvider) {
parser.getExtraTypeProviders().add((ExtraTypeProvider) processor);
}
if (processor instanceof ExtraProcessor) {
parser.getExtraProcessors().add((ExtraProcessor) processor);
}
if (processor instanceof FieldTypeResolver) {
parser.setFieldTypeResolver((FieldTypeResolver) processor);
}
}
// 获取所需要的类
T value = https://www.it610.com/article/(T) parser.parseObject(clazz, null);
parser.handleResovleTask(value);
parser.close();
return (T) value;
}
T value = https://www.it610.com/article/(T) parser.parseObject(clazz, null) 的代码如下，对于本例中的 User 对象，最终ObjectDeserializer会定位到类JavaBeanDeserializer，其 deserialze 代码有点长，就不贴出来了。
@SuppressWarnings("unchecked")
public T parseObject(Type type, Object fieldName) {
int token = lexer.token();
if (token == JSONToken.NULL) {
lexer.nextToken();
return null;
}
if (token == JSONToken.LITERAL_STRING) {
if (type == byte[].class) {
byte[] bytes = lexer.bytesValue();
lexer.nextToken();
return (T) bytes;
}
if (type == char[].class) {
String strVal = lexer.stringVal();
lexer.nextToken();
return (T) strVal.toCharArray();
}
}
// 根据输入的class类型，获取解析所需要的类
ObjectDeserializer derializer = config.getDeserializer(type);
try {
return (T) derializer.deserialze(this, type, fieldName);
} catch (JSONException e) {
throw e;
} catch (Throwable e) {
throw new JSONException(e.getMessage(), e);
}
}
其它用法 可以利用fastjson，将"1 2 3 4 5" 或 "1,2,3,4,5"这样的字符串，转换成数组。实际应用过程中，十分方便简洁。
@Test
public void testArray() {
String arrayString = "1 2 3 4 5";
int[] array1 = JSON.parseObject("[" + arrayString + "]", int[].class);
System.out.println(Arrays.toString(array1));
String boolString = "1, true, 0, false";
boolean[] array2 = JSON.parseObject("[" + boolString + "]", boolean[].class);
System.out.println(Arrays.toString(array2));
}
fastjson 的整理思路 总的来说，是定义了两个接口：ObjectSerializer 和 ObjectDeserializer 。针对不同的类，实现了不同的序列化和反序列化方式，并能够根据类的信息，选择合适的接口实现类。
总结 【FastJSON|FastJSON 源码分析】仅仅通过序列化、反序列化一个Java Bean对象，对fastjson的源码进行分析。很多地方没有展开讨论，至少没法通过博客的形式写出来，具体细节太多了。如果有什么问题，欢迎指正~
