javastruct关于java结构体.doc

javastructA library to treat java objects as C structs.窗体顶端 窗体底端Project HomeDownloadsWikiIssuesSourceSearch 窗体顶端 for 窗体底端HowToUseJavaStruct This page explains how to use JavaStruct library. Featured, Phase-ImplementationUpdated Feb 4, 2010 by IntroductionStruct classes can be used to greatly simplfy network protocol codes of Java applications when working with embedded devices and other applications which uses C style structs.Instead of manually encoding and decoding messages, JavaStruct allows programmers to treat java classes as c structs.JavaStruct uses Java 5 annotations to mark Classes and fields as structs. JavaStruct is not the first attempt to provide struct like functionality, Jean-Marie Dautelles Javolution library also has an excellent struct implementation. But instead of using special classes in Javolution, POJO approach is preferred JavaStruct.General usageJavaStruct faade class is used to pack and unpack struct classes. Below is a simple unit test method for checking a struct class. Struct fields hasan order value, because Java JVM specification does not tell anything about order of the class members. They are ordered as their appearance in Suns implementation but it differs on other JVMs. So every Struct field has to supply an order value.StructClasspublic class Foo StructField(order = 0) public byte b; StructField(order = 1) public int i;try / Pack the class as a byte buffer Foo f = new Foo(); /媒体处理器 f.b = (byte)1; f.i = 1; byte b = JavaStruct.pack(f); / Unpack it into an object Foo f2 = new Foo(); JavaStruct.unpack(f2, b);catch(StructException e)Struct operations throws a checked StructException if anything goes wrong.Struct classes can be used with Streams directly too. Please refer to Photoshop ACB file reader example.public void read(String acbFile) try FileInputStream fis = new FileInputStream(new File(acbFile); header = new ACBHeader(); StructUnpacker up = JavaStruct.getUnpacker(fis, ByteOrder.BIG_ENDIAN); up.readObject(header);.PrimitivesUsing primitives. Note that private and protected fields requires appropriate getter and setter methods. Transient fields are automatically excluded.StructClasspublic class PublicPrimitives implements Serializable StructField(order = 0) public byte b; StructField(order = 1) public char c; StructField(order = 2) public short s; StructField(order = 3) public int i; StructField(order = 4) public long lo; StructField(order = 5) protected float f; StructField(order = 6) private double d; transient int blah; transient double foo; public float getF() return f; public void setF(float f) this.f = f; public double getD() return d; public void setD(double d) this.d = d; public boolean equals(Object o) PublicPrimitives other = (PublicPrimitives)o; return (this.b = other.b & this.c = other.c & this.s = other.s & this.i = other.i & this.lo = other.lo & this.f = other.f & this.d = other.d); ArraysArrays have some prerequisites. When unpacking, sufficent space should be reserved in the array. Only arrays, whose lengths are defined in another field using ArrayLengthMarker (see below section) can be null, they are automatically allocated while unpacking. Other than that they can not be null and uninitialized.StructClasspublic class PublicPrimitiveArrays StructField(order = 0) public byte b = new byte5; StructField(order = 1) public char c = new byte10; StructField(order = 2) public short s; StructField(order = 3) public int i;Array Length MarkersArray length markers are very useful for the fields whose legth is defined in anoher field. consider the following example. This is a special String struct which has a length fields and length number of 16 bit characters following it. +-+-/-+ | Length | UTF-16 Characters | +-+-/-+In order to process this, we have to represent these strings as a special Struct class, lets say AStruct. The length field should be annotated as ArrayLengthMarker. This way javastruct can automatically use the value in length field while processing the array field during packing and unpacking operations.StructClasspublic class AString StructField (order = 0 ) ArrayLengthMarker (fieldName = chars) public int length; StructField (order = 1) public char chars; public AString(String content) this.length = content.length(); this.chars = content.toCharArray(); .Comment by , Dec 19, 2011Thanks for this example. But how to read a struct from buffer ?Comment by , Feb 10, 2012Is there anything special that needs to be done to allow this to work with 2D arrays?Here is the object that I am trying to packStructClasspublic class SEND_DATA_STRUCTURE StructField(order = 0) public float gyro_offset = new float3; StructField(order = 1) public float accel_offset = new float3; StructField(order = 2) public float MagCalRotationMat = new float33; StructField(order = 3) public float MagCalScaleMat = new float33; StructField(order = 4) public float MagCalShiftMat = new float13; Here is the code Im using to pack it:byte b; SEND_DATA_STRUCTURE txData = new SEND_DATA_STRUCTURE(); b = JavaStruct.pack(txData,ByteOrder.LITTLE_ENDIAN);and this is the runtime error that I get: struct.StructException?: struct.StructException?: No struct Annotation found for FIf I get rid of the 2D arrays, I dont get that exception.Comment by , Feb 6, 2013What if there are multiple fields in the