MessagePack枚举类的反序列化报错：Caused by: javassist.CannotCompileException: [source error] no such constructor: com.example..

问题1：

反序列化的枚举类：

@Message
public enum EnumClassd {
    Unknown   (0);
    @Getter
    @Setter
    private Integer code;
    EnumClassd(Integer code) {
        this.code = code;
    }

}

MessagePack反序列化上述枚举类时报错：

org.msgpack.MessageTypeException: org.msgpack.template.builder.TemplateBuildException: Cannot compile: 
{
  if (!$3 && $1.trySkipNil()) {
    return null;
  }
  com.example.EnumClass _$$_t;
  if ($2 == null) {
    _$$_t = new com.example.EnumClass();
  } else {
    _$$_t = (com.example.EnumClass) $2;
  }
  $1.readArrayBegin();
  if ($1.trySkipNil()) {  } else {
    org.msgpack.template.builder.DefaultBuildContext.readPrivateField($1, _$$_t, com.example.EnumClass.class, "code", templates[0]);
  }
  $1.readArrayEnd();
  return _$$_t;
}


    at org.msgpack.template.TemplateRegistry.buildAndRegister(TemplateRegistry.java:575)
    at org.msgpack.template.TemplateRegistry.lookupAfterBuilding(TemplateRegistry.java:472)
    at org.msgpack.template.TemplateRegistry.lookup(TemplateRegistry.java:251)
    at org.msgpack.template.builder.JavassistTemplateBuilder.toTemplate(JavassistTemplateBuilder.java:129)
    at org.msgpack.template.builder.JavassistTemplateBuilder.buildTemplate(JavassistTemplateBuilder.java:117)
    at org.msgpack.template.builder.AbstractTemplateBuilder.buildTemplate(AbstractTemplateBuilder.java:61)
    at org.msgpack.template.TemplateRegistry.buildAndRegister(TemplateRegistry.java:562)
    at org.msgpack.template.TemplateRegistry.lookupAfterBuilding(TemplateRegistry.java:472)
    at org.msgpack.template.TemplateRegistry.lookup(TemplateRegistry.java:251)
    at org.msgpack.template.TemplateRegistry.lookupGenericTypeImpl0(TemplateRegistry.java:320)
    at org.msgpack.template.TemplateRegistry.lookupGenericTypeImpl(TemplateRegistry.java:308)
    at org.msgpack.template.TemplateRegistry.lookupGenericType(TemplateRegistry.java:280)
    at org.msgpack.template.TemplateRegistry.lookup(TemplateRegistry.java:205)
    at org.msgpack.template.builder.JavassistTemplateBuilder.toTemplate(JavassistTemplateBuilder.java:129)
    at org.msgpack.template.builder.JavassistTemplateBuilder.buildTemplate(JavassistTemplateBuilder.java:117)
    at org.msgpack.template.builder.AbstractTemplateBuilder.buildTemplate(AbstractTemplateBuilder.java:61)
    at org.msgpack.template.TemplateRegistry.buildAndRegister(TemplateRegistry.java:562)
    at org.msgpack.template.TemplateRegistry.lookupAfterBuilding(TemplateRegistry.java:472)
    at org.msgpack.template.TemplateRegistry.lookup(TemplateRegistry.java:251)
    at org.msgpack.MessagePack.read(MessagePack.java:370)
    at com.example.jenkinscodehubtest.util.OsvfUtil.ReadNextBlock(OsvfUtil.java:61)
    at com.example.jenkinscodehubtest.JenkinsCodehubTestApplicationTests.deal(JenkinsCodehubTestApplicationTests.java:46)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.junit.platform.commons.util.ReflectionUtils.invokeMethod(ReflectionUtils.java:688)
    at org.junit.jupiter.engine.execution.MethodInvocation.proceed(MethodInvocation.java:60)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$ValidatingInvocation.proceed(InvocationInterceptorChain.java:131)
    at org.junit.jupiter.engine.extension.TimeoutExtension.intercept(TimeoutExtension.java:149)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestableMethod(TimeoutExtension.java:140)
    at org.junit.jupiter.engine.extension.TimeoutExtension.interceptTestMethod(TimeoutExtension.java:84)
    at org.junit.jupiter.engine.execution.ExecutableInvoker$ReflectiveInterceptorCall.lambda$ofVoidMethod$0(ExecutableInvoker.java:115)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.lambda$invoke$0(ExecutableInvoker.java:105)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain$InterceptedInvocation.proceed(InvocationInterceptorChain.java:106)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.proceed(InvocationInterceptorChain.java:64)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.chainAndInvoke(InvocationInterceptorChain.java:45)
    at org.junit.jupiter.engine.execution.InvocationInterceptorChain.invoke(InvocationInterceptorChain.java:37)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:104)
    at org.junit.jupiter.engine.execution.ExecutableInvoker.invoke(ExecutableInvoker.java:98)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.lambda$invokeTestMethod$6(TestMethodTestDescriptor.java:210)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.invokeTestMethod(TestMethodTestDescriptor.java:206)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:131)
    at org.junit.jupiter.engine.descriptor.TestMethodTestDescriptor.execute(TestMethodTestDescriptor.java:65)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:139)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
    at java.util.ArrayList.forEach(ArrayList.java:1249)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
    at java.util.ArrayList.forEach(ArrayList.java:1249)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.invokeAll(SameThreadHierarchicalTestExecutorService.java:38)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$5(NodeTestTask.java:143)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$7(NodeTestTask.java:129)
    at org.junit.platform.engine.support.hierarchical.Node.around(Node.java:137)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.lambda$executeRecursively$8(NodeTestTask.java:127)
    at org.junit.platform.engine.support.hierarchical.ThrowableCollector.execute(ThrowableCollector.java:73)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.executeRecursively(NodeTestTask.java:126)
    at org.junit.platform.engine.support.hierarchical.NodeTestTask.execute(NodeTestTask.java:84)
    at org.junit.platform.engine.support.hierarchical.SameThreadHierarchicalTestExecutorService.submit(SameThreadHierarchicalTestExecutorService.java:32)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestExecutor.execute(HierarchicalTestExecutor.java:57)
    at org.junit.platform.engine.support.hierarchical.HierarchicalTestEngine.execute(HierarchicalTestEngine.java:51)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:108)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:88)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.lambda$execute$0(EngineExecutionOrchestrator.java:54)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.withInterceptedStreams(EngineExecutionOrchestrator.java:67)
    at org.junit.platform.launcher.core.EngineExecutionOrchestrator.execute(EngineExecutionOrchestrator.java:52)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:96)
    at org.junit.platform.launcher.core.DefaultLauncher.execute(DefaultLauncher.java:75)
    at com.intellij.junit5.JUnit5IdeaTestRunner.startRunnerWithArgs(JUnit5IdeaTestRunner.java:71)
    at com.intellij.rt.junit.IdeaTestRunner$Repeater.startRunnerWithArgs(IdeaTestRunner.java:33)
    at com.intellij.rt.junit.JUnitStarter.prepareStreamsAndStart(JUnitStarter.java:220)
    at com.intellij.rt.junit.JUnitStarter.main(JUnitStarter.java:53)
Caused by: org.msgpack.template.builder.TemplateBuildException: Cannot compile: 
{
  if (!$3 && $1.trySkipNil()) {
    return null;
  }
  com.example.EnumClass _$$_t;
  if ($2 == null) {
    _$$_t = new com.example.EnumClass();
  } else {
    _$$_t = (com.example.EnumClass) $2;
  }
  $1.readArrayBegin();
  if ($1.trySkipNil()) {  } else {
    org.msgpack.template.builder.DefaultBuildContext.readPrivateField($1, _$$_t, com.example.EnumClass.class, "code", templates[0]);
  }
  $1.readArrayEnd();
  return _$$_t;
}

    at org.msgpack.template.builder.BuildContext.build(BuildContext.java:73)
    at org.msgpack.template.builder.DefaultBuildContext.buildTemplate(DefaultBuildContext.java:56)
    at org.msgpack.template.builder.JavassistTemplateBuilder.buildTemplate(JavassistTemplateBuilder.java:119)
    at org.msgpack.template.builder.AbstractTemplateBuilder.buildTemplate(AbstractTemplateBuilder.java:61)
    at org.msgpack.template.TemplateRegistry.buildAndRegister(TemplateRegistry.java:562)
    ... 86 more
Caused by: javassist.CannotCompileException: [source error] no such constructor: com.example.EnumClass
    at javassist.CtBehavior.setBody(CtBehavior.java:446)
    at javassist.CtBehavior.setBody(CtBehavior.java:412)
    at javassist.CtNewMethod.make(CtNewMethod.java:138)
    at org.msgpack.template.builder.BuildContext.buildReadMethod(BuildContext.java:144)
    at org.msgpack.template.builder.BuildContext.build(BuildContext.java:65)
    ... 90 more
Caused by: compile error: no such constructor: com.example.EnumClass
    at javassist.compiler.MemberCodeGen.atMethodCallCore2(MemberCodeGen.java:593)
    at javassist.compiler.MemberCodeGen.atMethodCallCore(MemberCodeGen.java:575)
    at javassist.compiler.MemberCodeGen.atNewExpr(MemberCodeGen.java:302)
    at javassist.compiler.ast.NewExpr.accept(NewExpr.java:73)
    at javassist.compiler.CodeGen.atAssignCore(CodeGen.java:860)
    at javassist.compiler.CodeGen.atVariableAssign(CodeGen.java:793)
    at javassist.compiler.CodeGen.atAssignExpr(CodeGen.java:747)
    at javassist.compiler.CodeGen.atStmnt(CodeGen.java:332)
    at javassist.compiler.ast.Stmnt.accept(Stmnt.java:50)
    at javassist.compiler.CodeGen.atStmnt(CodeGen.java:351)
    at javassist.compiler.ast.Stmnt.accept(Stmnt.java:50)
    at javassist.compiler.CodeGen.atIfStmnt(CodeGen.java:391)
    at javassist.compiler.CodeGen.atStmnt(CodeGen.java:355)
    at javassist.compiler.ast.Stmnt.accept(Stmnt.java:50)
    at javassist.compiler.CodeGen.atStmnt(CodeGen.java:351)
    at javassist.compiler.ast.Stmnt.accept(Stmnt.java:50)
    at javassist.compiler.CodeGen.atMethodBody(CodeGen.java:292)
    at javassist.compiler.Javac.compileBody(Javac.java:223)
    at javassist.CtBehavior.setBody(CtBehavior.java:438)
    ... 94 more

Disconnected from the target VM, address: '127.0.0.1:54789', transport: 'socket'

Process finished with exit code -1

解决方法：

将注解@Message改为注解@MessagePackOrdinalEnum即可解决(https://github.com/msgpack/msgpack/issues/66)

问题2：

Exception in thread "main" org.msgpack.MessageTypeException: Expected raw value, but got boolean
    at org.msgpack.unpacker.Accept.acceptBoolean(Accept.java:33)
    at org.msgpack.unpacker.MessagePackUnpacker.readOneWithoutStackLarge(MessagePackUnpacker.java:154)
    at org.msgpack.unpacker.MessagePackUnpacker.readOneWithoutStack(MessagePackUnpacker.java:139)
    at org.msgpack.unpacker.MessagePackUnpacker.readOne(MessagePackUnpacker.java:73)
    at org.msgpack.unpacker.MessagePackUnpacker.readString(MessagePackUnpacker.java:502)
    at org.msgpack.template.StringTemplate.read(StringTemplate.java:46)
    at org.msgpack.template.StringTemplate.read(StringTemplate.java:25)
    at org.msgpack.template.AbstractTemplate.read(AbstractTemplate.java:31)
    at com.my.msgpack.SimpleMessagePackPractice$MyMessage2_$$_Template_1305193908_1.read(SimpleMessagePackPractice$MyMessage2_$$_Template_1305193908_1.java)
    at org.msgpack.template.AbstractTemplate.read(AbstractTemplate.java:31)
    at org.msgpack.MessagePack.read(MessagePack.java:388)
    at org.msgpack.MessagePack.read(MessagePack.java:371)
    at com.my.msgpack.SimpleMessagePackPractice.main(SimpleMessagePackPractice.java:61)

 该报错是因为MessagePack序列化的结果中只包含了value，而不包含key。因而在进行反序列化需要保证类中属性的顺序必须保证完全一致，否则就会出错：

如果两个属性的类型一致，可以反序列化，但是值发生错乱。
如果两个属性的类型不一致，会抛出类型不匹配异常。
因此解决方法是报错序列化和反序列化的对象顺序类型保持一致。
 
 
MessagePack详情见下文：

一、MessagePack是什么

先看官方的定义：MessagePack是一种高效的二进制序列化格式。它允许您像JSON一样在多个语言之间交换数据。但是，它更快并且更小。

 

从官方定义中，可以有如下的结论：

  1. MessagePack是一个二进制序列化格式，因而它序列化的结果可以在多个语言间进行数据的交换。

  2. 从性能上讲，它要比json的序列化格式要好。

  3. 从结果大小上讲，它要比json的序列化结果要小。

 

但是官方并没有提MessagePack和google pb的对比，实际上从空间和时间两个方面对比，pb均要优于MessagePack，但pb相对MessagePack 的缺点是支持的语言种类比较少，需要编写专门的 .proto文件，使用上没有MessagePack方便。

二、MessagePack的主要概念

 

2.1 type system

类型体系是MessagePack的基础，也是MessagePack在序列化后比json占用空间小的关键。当前包含的type有如下几类：
  • Integer represents an integer
  • Nil represents nil
  • Boolean represents true or false
  • Float represents a IEEE 754 double precision floating point number including NaN and Infinity
  • Raw
    • String extending Raw type represents a UTF-8 string
    • Binary extending Raw type represents a byte array
  • Array represents a sequence of objects
  • Map represents key-value pairs of objects
  • Extension represents a tuple of type information and a byte array where type information is an integer whose meaning is defined by applications or MessagePack specification
    • Timestamp represents an instantaneous point on the time-line in the world that is independent from time zones or calendars. Maximum precision is nanoseconds.
 
这个类型体系将我们在代码开发中用到的数据格式进行了映射，并且通过Extension这个类型给使用者留出了自由扩充的空间，但由于表示形式的限制，当前Extension最多有127个。
 
每一种类型能够表示的范围可以查看MessagePack规范中的Limitation部分和Extension types部分。

2.2 formats

在MessagePack中一个value的组成格式是这样的：类型[长度][data]。下面列出几个示例，详细完整的描述请看附录中的MessagePack规范。
 

2.2.1常量型

比如对于null、true、false这三个值，在MessagePack会被固定的映射为如下的值。
format name
first byte (in binary)
first byte (in hex)
nil
11000000
0xc0
false
11000010
0xc2
true
11000011
0xc3

2.2.2 int型（包含有符号整数和无符号整数）

 
示例如下 
  • 0xcc表示当前的值的类型是无符号整数并且长度不超过8个bit，具体的值内容需要通过后续8个bit位的内容来计算
  • 0xcd表示当前的值的类型是无符号整数并且长度不超过16个bit，具体的值内容需要通过后续16个bit位的内容来计算
  • 0xd0表示当前的值的类型是有符号整数并且长度不超过8个bit，具体的值内容需要通过后续8个bit位的内容来计算
  • 0xd1表示当前的值的类型是有符号整数并且长度不超过16个bit，具体的值内容需要通过后续16个bit位的内容来计算
uint 8 stores a 8-bit unsigned integer  
+--------+--------+
|  0xcc  |ZZZZZZZZ|
+--------+--------+

uint 16 stores a 16-bit big-endian unsigned integer
+--------+--------+--------+
|  0xcd  |ZZZZZZZZ|ZZZZZZZZ|
+--------+--------+--------+

int 8 stores a 8-bit signed integer
+--------+--------+
|  0xd0  |ZZZZZZZZ|
+--------+--------+

int 16 stores a 16-bit big-endian signed integer
+--------+--------+--------+
|  0xd1  |ZZZZZZZZ|ZZZZZZZZ|
+--------+--------+--------+

2.2.3 字符串 

  • 0xd9表示当前的值的类型是字符串并且长度不超过(2^8)-1个bytes ，具体的长度需要通过后续8个bit位的内容来计算，字符串的具体内容是后续长度的byte所表示的内容
  • 0xda表示当前的值的类型是字符串并且长度不超过(2^16)-1个bytes ，具体的长度需要通过后续16个bit位的内容来计算，字符串的具体内容是后续长度的byte所表示的内容
str 8 stores a byte array whose length is upto (2^8)-1 bytes:
+--------+--------+========+
|  0xd9  |YYYYYYYY|  data  |
+--------+--------+========+

str 16 stores a byte array whose length is upto (2^16)-1 bytes:
+--------+--------+--------+========+
|  0xda  |ZZZZZZZZ|ZZZZZZZZ|  data  |
+--------+--------+--------+========+

2.2.4 数组 

  • 0xdc表示当前的值的类型是数组并且长度不超过(2^16)-1个元素 ，具体的长度需要通过后续16个bit位（两个byte）的内容来计算，计算出来的值就是数组元素的个数
  • 0xdd表示当前的值的类型是数组并且长度不超过(2^32)-1个元素 ，具体的长度需要通过后续32个bit位（4个byte）的内容来计算，计算出来的值就是数组元素的个数
array 16 stores an array whose length is upto (2^16)-1 elements:
+--------+--------+--------+~~~~~~~~~~~~~~~~~+
|  0xdc  |YYYYYYYY|YYYYYYYY|    N objects    |
+--------+--------+--------+~~~~~~~~~~~~~~~~~+

array 32 stores an array whose length is upto (2^32)-1 elements:
+--------+--------+--------+--------+--------+~~~~~~~~~~~~~~~~~+
|  0xdd  |ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|ZZZZZZZZ|    N objects    |
+--------+--------+--------+--------+--------+~~~~~~~~~~~~~~~~~+

2.2.5 小结

 

2.3 Serialization：type to format conversion

 
source types
output format
Integer
int format family (positive fixint, negative fixint, int 8/16/32/64 or uint 8/16/32/64)
Nil
nil
Boolean
bool format family (false or true)
Float
float format family (float 32/64)
String
str format family (fixstr or str 8/16/32)
Binary
bin format family (bin 8/16/32)
Array
array format family (fixarray or array 16/32)
Map
map format family (fixmap or map 16/32)
Extension
ext format family (fixext or ext 8/16/32)

 

If an object can be represented in multiple possible output formats, serializers SHOULD use the format which represents the data in the smallest number of bytes.

2.4 Deserialization: format to type conversion

source formats
output type
positive fixint, negative fixint, int 8/16/32/64 and uint 8/16/32/64
Integer
nil
Nil
false and true
Boolean
float 32/64
Float
fixstr and str 8/16/32
String
bin 8/16/32
Binary
fixarray and array 16/32
Array
fixmap map 16/32
Map
fixext and ext 8/16/32
Extension

 

三、为什么MessagePack比json序列化使用的字节流更少 

3.1 直观对比

可以通过下图的两张图简单进行下对比，第一张图是同一个数据类型的内容用json和messagepack序列化的结果。

 从第二张图可以明显看到messagepack要比json占用的空间更少。

3.2 序列化结果只有value且value进行了专属映射

 这张图是MessagePack官网上的，用来进行json和MessagePack序列化结果的对比，实际情况是否确实如此呢？

我本地使用的msgpack-0.6.12版本。
代码如下：
public class MessagePackSerializationCompareJson {

    @Message // Annotation
    public static class MyMessage {
        // public fields are serialized.
        public boolean compact;
        public int schema;
        
        public  String toString() {
            return "compact:"+compact+";schema:"+schema;
        }

    }
    /**
     * 
     * @param args
     * @throws IOException 
     */
    public static void main(String[] args) throws IOException {
      //初始化一个对象
        MyMessage src = new MyMessage();
        src.compact = true;
        src.schema=0;
        
      //利用MessagePack进行序列化
        MessagePack msgpack = new MessagePack();
        // Serialize
        byte[] bytes = msgpack.write(src);
        System.out.println("msgpack result length:"+bytes.length);
        
        //利用json进行序列化
        String jsonResult = JSONObject.toJSON(src).toString();
        System.out.println("json result length:"+jsonResult.getBytes().length);
        
    }

}

运行结果如下：

json result length:27
msgpack result length:3

json序列化的结果是27，和官网图片中的结果相同。但MessagePack的序列化结果是3，要比官网中的数字小很多。
按照上面图片的解释应当是：
  • 第一个byte是82，表示序列化后的结果有两个元素
  • 第二个byte是c3，表示第一个元素的值是true
  • 第三个byte是00，表示第二个元素的值是0
 
为了验证我们的推测，我们可以在MyMessage类中再添加一个boolean类型的属性，但不给这个属性赋值，按照java的规范，这个属性的值就是false，按照MessagePack的规范，就会被转为一个byte的c2，这样msgpack序列化后的长度值就是4.  而json序列化的增加值要增加不少，是属性名称的长度+5（false的长度）+4（要增加两个双引号，一个逗号，一个冒号），如果属性名称长度是4，则一共会增加13个byte，总长度就是40.
public class MessagePackSerializationCompareJson {

    @Message // Annotation
    public static class MyMessage {
        // public fields are serialized.
        public boolean compact;
        public int schema;
        public boolean link;
        
        
        public  String toString() {
            return "compact:"+compact+";schema:"+schema+";link:"+link;
        }

    }
    /**
     * 
     * @param args
     * @throws IOException 
     */
    public static void main(String[] args) throws IOException {
      //初始化一个对象
        MyMessage src = new MyMessage();
        src.compact = true;
        src.schema=0;
        
      //利用json进行序列化
        String jsonResult = JSONObject.toJSON(src).toString();
        System.out.println("json result length:"+jsonResult.getBytes().length);
        
      //利用MessagePack进行序列化
        MessagePack msgpack = new MessagePack();
        // Serialize
        byte[] bytes = msgpack.write(src);
        System.out.println("msgpack result length:"+bytes.length);
        
    }

}

上面代码的执行的结果也符合猜测：

json result length:40
msgpack result length:4

从这个数字上看，MessagePack明显优于json，特别是在属性多的情况下差距会更大。即使json中把key去掉，序列化后的结果也要比MessagePack占用的空间大。
 

3.2 序列化对象的属性顺序不能变动

3.1分析了MessagePack序列化的结果中只包含了value，而不包含key。因而在进行反序列化需要保证类中属性的顺序必须保证完全一致，否则就会出错：
如果两个属性的类型一致，可以反序列化，但是值发生错乱。
如果两个属性的类型不一致，会抛出类型不匹配异常。
 

3.2.1 顺序不同，类型相同

public class SimpleMessagePackPractice {

    @Message // Annotation
    public static class MyMessage {
        // public fields are serialized.
        public boolean compact;
        public boolean link;

        public String toString() {
            return "link:" + link + ";compact:" + compact;
        }
    }

    @Message // Annotation
    public static class MyMessage2 {
        // public fields are serialized.
        public boolean link;
        public boolean compact;

        public String toString() {
            return "link:" + link + ";compact:" + compact;
        }
    }

    /**
     * 
     * @param args
     * @throws IOException 
     */
    public static void main(String[] args) throws IOException {

        //初始化一个对象
        MyMessage src = new MyMessage();
        src.compact = true;
        src.link = false;

        //利用MessagePack进行序列化
        MessagePack msgpack = new MessagePack();
        // Serialize
        byte[] bytes = msgpack.write(src);

        //利用MessagePack进行反序列化
        MyMessage2 dst = msgpack.read(bytes, MyMessage2.class);
        System.out.println("msgpack 原始数据:" + src);
        System.out.println("msgpack 反序列化:" + dst);
        
        
    }

}

上述代码的执行结果如下：

msgpack 原始数据:link:false;compact:true
msgpack 反序列化:link:true;compact:false

3.2.1 顺序不同，类型不同

public class SimpleMessagePackPractice {

    @Message // Annotation
    public static class MyMessage {
        // public fields are serialized.
        public boolean compact;
        public String link;

        public String toString() {
            return "link:" + link + ";compact:" + compact;
        }
    }

    @Message // Annotation
    public static class MyMessage2 {
        // public fields are serialized.
        public String link;
        public boolean compact;

        public String toString() {
            return "link:" + link + ";compact:" + compact;
        }
    }

    /**
     * 
     * @param args
     * @throws IOException 
     */
    public static void main(String[] args) throws IOException {

        //初始化一个对象
        MyMessage src = new MyMessage();
        src.compact = true;
        src.link = "www.baidu.com";

        //利用MessagePack进行序列化
        MessagePack msgpack = new MessagePack();
        // Serialize
        byte[] bytes = msgpack.write(src);

        //利用MessagePack进行反序列化
        MyMessage2 dst = msgpack.read(bytes, MyMessage2.class);
        System.out.println("msgpack 原始数据:" + src);
        System.out.println("msgpack 反序列化:" + dst);
        
        
    }

}

执行结果：

Exception in thread "main" org.msgpack.MessageTypeException: Expected raw value, but got boolean
    at org.msgpack.unpacker.Accept.acceptBoolean(Accept.java:33)
    at org.msgpack.unpacker.MessagePackUnpacker.readOneWithoutStackLarge(MessagePackUnpacker.java:154)
    at org.msgpack.unpacker.MessagePackUnpacker.readOneWithoutStack(MessagePackUnpacker.java:139)
    at org.msgpack.unpacker.MessagePackUnpacker.readOne(MessagePackUnpacker.java:73)
    at org.msgpack.unpacker.MessagePackUnpacker.readString(MessagePackUnpacker.java:502)
    at org.msgpack.template.StringTemplate.read(StringTemplate.java:46)
    at org.msgpack.template.StringTemplate.read(StringTemplate.java:25)
    at org.msgpack.template.AbstractTemplate.read(AbstractTemplate.java:31)
    at com.my.msgpack.SimpleMessagePackPractice$MyMessage2_$$_Template_1305193908_1.read(SimpleMessagePackPractice$MyMessage2_$$_Template_1305193908_1.java)
    at org.msgpack.template.AbstractTemplate.read(AbstractTemplate.java:31)
    at org.msgpack.MessagePack.read(MessagePack.java:388)
    at org.msgpack.MessagePack.read(MessagePack.java:371)
    at com.my.msgpack.SimpleMessagePackPractice.main(SimpleMessagePackPractice.java:61)

参考：https://www.i4k.xyz/article/dly41721/101995555

参考：https://github.com/msgpack/msgpack/blob/master/spec.md

posted @ 2021-10-12 14:05  vickylinj  阅读(1751)  评论(0)  编辑  收藏  举报