FST 的概念和定义
FST 序列化全称是 Fast Serialization Tool,它是对 Java 序列化的替换实现。既然前文中提到 Java 序列化的两点严重不足,在 FST 中得到了较大的改善,FST 的特征如下:
JDK 提供的序列化提升了 10 倍,体积也减少 3-4 倍多
支持堆外 Maps,和堆外 Maps 的持久化
支持序列化为 JSON
FST 序列化的使用
FST 的使用有两种方式,一种是快捷方式,另一种需要使用 ObjectOutput 和 ObjectInput。
直接使用 FSTConfiguration 提供的序列化和反序列化接口
<pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" cid="n19" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public static void serialSample() {
FSTConfiguration conf = FSTConfiguration.createAndroidDefaultConfiguration();
User object = new User();
object.setName("huaijin");
object.setAge(30);
System.out.println("serialization, " + object);
byte[] bytes = conf.asByteArray(object);
User newObject = (User) conf.asObject(bytes);
System.out.println("deSerialization, " + newObject);
}</pre>
FSTConfiguration 也提供了注册对象的 Class 接口,如果不注册,默认会将对象的 Class Name 写入。这个提供了易用高效的 API 方式,不使用 ByteArrayOutputStreams 而直接得到 byte[]。
使用 ObjectOutput 和 ObjectInput,能更细腻控制序列化的写入写出:
<pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" cid="n24" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">static FSTConfiguration conf = FSTConfiguration.createAndroidDefaultConfiguration();
static void writeObject(OutputStream outputStream, User user) throws IOException {
FSTObjectOutput out = conf.getObjectOutput(outputStream); out.writeObject(user);
out.close();}
static FstObject readObject(InputStream inputStream) throws Exception { FSTObjectInput input = conf.getObjectInput(inputStream);
User fstObject = (User) input.readObject(User.class); input.close();
return fstObject;}</pre>
FST 在 Dubbo 中的应用
Dubbo 中对 FstObjectInput 和 FstObjectOutput 重新包装解决了序列化和反序列化空指针的问题。
并且构造了 FstFactory 工厂类,使用工厂模式生成 FstObjectInput 和 FstObjectOutput。其中同时使用单例模式,控制整个应用中 FstConfiguration 是单例,并且在初始化时将需要序列化的对象全部注册到 FstConfiguration。
对外提供了同一的序列化接口 FstSerialization,提供 serialize 和 deserialize 能力。
FST 序列化/反序列化
FST 序列化存储格式
基本上所有以 Byte 形式存储的序列化对象都是类似的存储结构,不管 class 文件、so 文件、dex 文件都是类似,这方面没有什么创新的格式,最多是在字段内容上做了一些压缩优化,包括我们最常使用的 utf-8 编码都是这个做法。
FST 的序列化存储和一般的字节格式化存储方案也没有标新立异的地方,比如下面这个 FTS 的序列化字节文件
<pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" cid="n41" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">00000001: 0001 0f63 6f6d 2e66 7374 2e46 5354 4265
00000010: 616e f701 fc05 7630 7374 7200 </pre>
格式:
<pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" cid="n44" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">
Header|类名长度|类名String|字段1类型(1Byte) | [长度] | 内容|字段2类型(1Byte) | [长度] | 内容|…</pre>
0000:字节数组类型:00 标识 OBJECT
0001:类名编码,00 标识 UTF 编码,01 表示 ASCII 编码
0002:Length of class name (1Byte) = 15
0003~0011:Class name string (15Byte)
0012:Integer 类型标识 0xf7
0013:Integer 的值=1
0014:String 类型标识 0xfc
0015:String 的长度=5
0016~001a:String 的值"v0str"
001b~001c:END
从上面可以看到 Integer 类型序列化后只占用了一个字节(值等于 1),并不像在内存中占用 4Byte,所以可以看出是根据一定规则做了压缩,具体代码看FSTObjectInput#instantiateSpecialTag
中对不同类型的读取,FSTObjectInput 也定义不同类型对应的枚举值:
<pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" cid="n71" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class FSTObjectOutput implements ObjectOutput {
private static final FSTLogger LOGGER = FSTLogger.getLogger(FSTObjectOutput.class);
public static Object NULL_PLACEHOLDER = new Object() {
public String toString() { return "NULL_PLACEHOLDER"; }};
public static final byte SPECIAL_COMPATIBILITY_OBJECT_TAG = -19; // see issue 52
public static final byte ONE_OF = -18;
public static final byte BIG_BOOLEAN_FALSE = -17;
public static final byte BIG_BOOLEAN_TRUE = -16;
public static final byte BIG_LONG = -10;
public static final byte BIG_INT = -9;
public static final byte DIRECT_ARRAY_OBJECT = -8;
public static final byte HANDLE = -7;
public static final byte ENUM = -6;
public static final byte ARRAY = -5;
public static final byte STRING = -4;
public static final byte TYPED = -3; // var class == object written class
public static final byte DIRECT_OBJECT = -2;
public static final byte NULL = -1;
public static final byte OBJECT = 0;
protected FSTEncoder codec;
...
}</pre>
FST 序列化和反序列化原理
对 Object 进行 Byte 序列化,相当于做了持久化的存储,在反序列的时候,如果 Bean 的定义发生了改变,那么反序列化器就要做兼容的解决方案,我们知道对于 JDK 的序列化和反序列,serialVersionUID 对版本控制起了很重要的作用。FST 对这个问题的解决方案是通过 @Version 注解进行排序。
在进行反序列操作的时候,FST 会先反射或者对象 Class 的所有成员,并对这些成员进行了排序,这个排序对兼容起了关键作用,也就是 @Version 的原理。在 FSTClazzInfo 中定义了一个 defFieldComparator 比较器,用于对 Bean 的所有 Field 进行排序:
<pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" cid="n78" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public final class FSTClazzInfo {
public static final Comparator<FSTFieldInfo> defFieldComparator = new Comparator<FSTFieldInfo>() {
@Override
public int compare(FSTFieldInfo o1, FSTFieldInfo o2) {
int res = 0;
if ( o1.getVersion() != o2.getVersion() ) {
return o1.getVersion() < o2.getVersion() ? -1 : 1;
}
// order: version, boolean, primitives, conditionals, object references
if (o1.getType() == boolean.class && o2.getType() != boolean.class) {
return -1;
}
if (o1.getType() != boolean.class && o2.getType() == boolean.class) {
return 1;
}
if (o1.isConditional() && !o2.isConditional()) {
res = 1;
} else if (!o1.isConditional() && o2.isConditional()) { res = -1;
} else if (o1.isPrimitive() && !o2.isPrimitive()) { res = -1;
} else if (!o1.isPrimitive() && o2.isPrimitive()) res = 1;
// if (res == 0) // 64 bit / 32 bit issues
// res = (int) (o1.getMemOffset() - o2.getMemOffset());
if (res == 0)
res = o1.getType().getSimpleName().compareTo(o2.getType().getSimpleName()); if (res == 0)
res = o1.getName().compareTo(o2.getName());
if (res == 0) { return o1.getField().getDeclaringClass().getName().compareTo(o2.getField().getDeclaringClass().getName());
}
return res;
}
};
...
}</pre>
从代码实现上可以看到,比较的优先级是 Field 的 Version 大小,然后是 Field 类型,所以总的来说 Version 越大排序越靠后,至于为什么要排序,看下 FSTObjectInput#instantiateAndReadNoSer 方法
<pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" cid="n83" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class FSTObjectInput implements ObjectInput {
protected Object instantiateAndReadNoSer(Class c, FSTClazzInfo clzSerInfo, FSTClazzInfo.FSTFieldInfo referencee, int readPos) throws Exception { Object newObj; newObj = clzSerInfo.newInstance(getCodec().isMapBased());
...
} else {
FSTClazzInfo.FSTFieldInfo[] fieldInfo = clzSerInfo.getFieldInfo(); readObjectFields(referencee, clzSerInfo, fieldInfo, newObj,0,0); }
return newObj;
}
protected void readObjectFields(FSTClazzInfo.FSTFieldInfo referencee, FSTClazzInfo serializationInfo, FSTClazzInfo.FSTFieldInfo[] fieldInfo, Object newObj, int startIndex, int version) throws Exception {
if ( getCodec().isMapBased() ) {
readFieldsMapBased(referencee, serializationInfo, newObj); if ( version >= 0 && newObj instanceof Unknown == false) getCodec().readObjectEnd();
return;
}
if ( version < 0 )
version = 0;
int booleanMask = 0;
int boolcount = 8;
final int length = fieldInfo.length;
int conditional = 0;
for (int i = startIndex; i < length; i++) { // 注意这里的循环
try {
FSTClazzInfo.FSTFieldInfo subInfo = fieldInfo[i]; if (subInfo.getVersion() > version ) { // 需要进入下一个版本的迭代
int nextVersion = getCodec().readVersionTag(); // 对象流的下一个版本
if ( nextVersion == 0 ) // old object read
{
oldVersionRead(newObj);
return;
}
if ( nextVersion != subInfo.getVersion() ) { // 同一个Field的版本不允许变,并且版本变更和流的版本保持同步
throw new RuntimeException("read version tag "+nextVersion+" fieldInfo has "+subInfo.getVersion());
} readObjectFields(referencee,serializationInfo,fieldInfo,newObj,i,nextVersion); // 开始下一个Version的递归
return;
}
if (subInfo.isPrimitive()) {
...
} else {
if ( subInfo.isConditional() ) {
...
} // object 把读出来的值保存到FSTFieldInfo中 Object subObject = readObjectWithHeader(subInfo); subInfo.setObjectValue(newObj, subObject);
}
...</pre>
从这段代码的逻辑基本就可以知道 FST 的序列化和反序列化兼容的原理了,注意里面的循环,正是按照排序后的 Filed 进行循环,而每个 FSTFieldInfo 都记录自己在对象流中的位置、类型等详细信息:
序列化:
按照 Version 对 Bean 的所有 Field 进行排序(不包括 static 和 transient 修饰的 member),没有 @Version 注解的 Field 默认 version=0;如果 version 相同,按照 version, boolean, primitives, conditionals, object references 排序
按照排序的 Field 把 Bean 的 Field 逐个写到输出流
@Version 的版本只能加不能减小,如果相等的话,有可能因为默认的排序规则,导致流中的 Filed 顺序和内存中的 FSTFieldInfo[]数组的顺序不一致,而注入错误
反序列化:
反序列化按照对象流的格式进行解析,对象流中保存的 Field 顺序和内存中的 FSTFieldInfo 顺序保持一致
相同版本的 Field 在对象流中存在,在内存 Bean 中缺失:可能抛异常(会有后向兼容问题)
对象流中包含内存 Bean 中没有的高版本 Field:正常(老版本兼容新)
相同版本的 Field 在对象流中缺失,在内存 Bean 中存在:抛出异常
相同的 Field 在对象流和内存 Bean 中的版本不一致:抛出异常
内存 Bean 增加了不高于最大版本的 Field:抛出异常
所以从上面的代码逻辑就可以分析出这个使用规则:@Version 的使用原则就是,每新增一个 Field,就对应的加上 @Version 注解,并且把 version 的值设置为当前版本的最大值加一,不允许删除 Field
另外再看一下 @Version 注解的注释:明确说明了用于后向兼容
<pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" cid="n114" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">package org.nustaq.serialization.annotations;
import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD})
/**
* support for adding fields without breaking compatibility to old streams.
* For each release of your app increment the version value. No Version annotation means version=0.
* Note that each added field needs to be annotated.
*
* e.g.
*
* class MyClass implements Serializable {
*
* // fields on initial release 1.0
* int x;
* String y;
*
* // fields added with release 1.5
* @Version(1) String added;
* @Version(1) String alsoAdded;
*
* // fields added with release 2.0
* @Version(2) String addedv2;
* @Version(2) String alsoAddedv2;
*
* }
*
* If an old class is read, new fields will be set to default values. You can register a VersionConflictListener
* at FSTObjectInput in order to fill in defaults for new fields.
*
* Notes/Limits:
* - Removing fields will break backward compatibility. You can only Add new fields.
* - Can slow down serialization over time (if many versions)
* - does not work for Externalizable or Classes which make use of JDK-special features such as readObject/writeObject
* (AKA does not work if fst has to fall back to 'compatible mode' for an object).
* - in case you use custom serializers, your custom serializer has to handle versioning
*
*/public @interface Version {
byte value();
}</pre>
<pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" cid="n117" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class FSTBean implements Serializable {
/** serialVersionUID */
private static final long serialVersionUID = -2708653783151699375L; private Integer v0in
private String v0str;
}</pre>
准备序列化和反序列化方法
<pre class="md-fences md-end-block ty-contain-cm modeLoaded" spellcheck="false" lang="java" cid="n120" mdtype="fences" style="box-sizing: border-box; overflow: visible; font-family: var(--monospace); font-size: 0.9em; display: block; break-inside: avoid; text-align: left; white-space: normal; background-image: inherit; background-position: inherit; background-size: inherit; background-repeat: inherit; background-attachment: inherit; background-origin: inherit; background-clip: inherit; background-color: rgb(248, 248, 248); position: relative !important; border: 1px solid rgb(231, 234, 237); border-radius: 3px; padding: 8px 4px 6px; margin-bottom: 15px; margin-top: 15px; width: inherit; color: rgb(51, 51, 51); font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: 400; letter-spacing: normal; orphans: 2; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-thickness: initial; text-decoration-style: initial; text-decoration-color: initial;">public class FSTSerial {
private static void serialize(FstSerializer fst, String fileName) { try {
FSTBean fstBean = new FSTBean();
fstBean.setV0int(1);
fstBean.setV0str("v0str");
byte[] v1 = fst.serialize(fstBean);
FileOutputStream fos = new FileOutputStream(new File("byte.bin")); fos.write(v1, 0, v1.length);
fos.close();
} catch (Exception e) {
e.printStackTrace();
}
}
private static void deserilize(FstSerializer fst, String fileName) { try {
FileInputStream fis = new FileInputStream(new File("byte.bin")); ByteArrayOutputStream baos = new ByteArrayOutputStream(); byte[] buf = new byte[256];
int length = 0;
while ((length = fis.read(buf)) > 0) {
baos.write(buf, 0, length);
}
fis.close();
buf = baos.toByteArray();
FSTBean deserial = fst.deserialize(buf, FSTBean.class); System.out.println(deserial);
System.out.println(deserial);
} catch (Exception e) {
e.printStackTrace();
}
}
public static void main(String[] args) {
FstSerializer fst = new FstSerializer();
serialize(fst, "byte.bin");
deserilize(fst, "byte.bin");
}
}</pre>