Java数据报之失序和丢包

习惯了TCP编程，认为UDP可以包办这些问题是错误的。一个UDP应用程序要承担可靠性方面的全部工作，包括报文的丢失、重复、时延、乱序以及连接失效等问题。

通常我们在可靠性好，传输时延小的局域网上开发测试，一些问题不容易暴露，但在大型互联网上却会出现错误。

UDP协议把递送的可靠性责任推到了上层即应用层，下面简单编写了几个类来专门处理两个问题：乱序和丢包。

四个类：DataPacket 类，PacketHeader类，PacketBody类

，DataEntry类，位于同一个文件DataPacket .java中。

DataPacket 类相当于一个门面模式，提供给外部使用，通信数据也在这个类中处理。

package com.skysoft.pcks;

import java.io.*;

import java.net.*;

import java.util.*;

public class  DataPacket {

InputStream is;

OutputStream os;

PacketHeader header;

PacketBody body;

ArrayList al;

public static final int DataSwapSize =

64532;

public DataPacket() {

header = new

PacketHeader();

body = new

PacketBody();

al = new

ArrayList();

}

public DataPacket(String file) {

this();

try {

is =

new FileInputStream(file);

header.CalcHeaderInfo(is.available());

this.madeBody();

is.close();

//this.Gereratedata();

}

catch

(FileNotFoundException ex) {

ex.printStackTrace();

}

catch (IOException ex1)

{

ex1.printStackTrace();

}

}

public DataPacket(URL url) {

this();

try {

//is

= url.openStream();

URLConnection conn=url.openConnection();

is=conn.getInputStream();

int

total=conn.getContentLength();

header.CalcHeaderInfo(total);

this.madeBody();

//System.out.println(total+":"+total);

is.close();

}

catch (IOException ex)

{

ex.printStackTrace();

}

}

private void madeBody() {

al.clear();

byte[] buffer;

DataEntry de;

for (int i = 0; i

< header.fragmentcounter; i++) {

try

{

ByteArrayOutputStream bos = new

ByteArrayOutputStream();

//is.skip(i * body.BODY_BUFFER_SIZE);

header.ArrageSort(i);

de = new

DataEntry(PacketBody.BODY_BUFFER_SIZE);

de.setSn(i);

de.setStreamsize(header.getStreamsize());

de.setFragmentcounter(header.getFragmentcounter());

if (header.isWTailFragment(i)) {

buffer = new

byte[header.getMinfragment()];

is.read(buffer, 0,

buffer.length);

header.setActByteSize(header.getMinfragment());

de.setActByteSize(header.getMinfragment());

}

else {

buffer = new

byte[body.BODY_BUFFER_SIZE];

is.read(buffer, 0,

buffer.length);

}

//System.out.println("length-------"+i+"

"+body.getBody().length+" "+header.getMinfragment());

body.setBody(buffer);

//System.out.println("length:" + i + " " +

header.toString());

bos.write(header.getByte(), 0,

header.HEADER_BUFFER_SIZE);

bos.write(body.getBody(), 0,

body.getBody().length);

de.setBytes(bos.toByteArray());

al.add(de);

}

catch

(IOException ex) {

ex.printStackTrace();

}

}

}

private void madeBody1() {

al.clear();

for (int i = 0; i

< header.fragmentcounter; i++) {

try

{

if (header.isWTailFragment(i))

is.read(body.getBody(), i *

body.BODY_BUFFER_SIZE,

header.getMinfragment());

else

is.read(body.getBody(), i *

body.BODY_BUFFER_SIZE,

body.BODY_BUFFER_SIZE);

ByteArrayOutputStream bos = new

ByteArrayOutputStream();

bos.write(header.getByte(), 0,

header.HEADER_BUFFER_SIZE);

bos.write(body.getBody(),

header.HEADER_BUFFER_SIZE,

body.getBody().length);

al.add(bos);

}

catch

(IOException ex) {

ex.printStackTrace();

}

}

}

public void Add(byte[] b1) {

byte[] buffer = (byte[])

b1.clone();

handlerText(buffer);

DataEntry de = new

DataEntry(buffer, header.getActByteSize());

de.setSn(header.getSn());

de.setStreamsize(header.getStreamsize());

de.setFragmentcounter(header.getFragmentcounter());

al.add(de);

}

private void handlerText(byte[] buffer)

{

ByteArrayOutputStream

baos = new ByteArrayOutputStream();

baos.write(buffer, 0,

header.HEADER_BUFFER_SIZE);

byte[] b=new

byte[header.HEADER_BUFFER_SIZE];

System.arraycopy(buffer,0,b,0,b.length);

ByteArrayInputStream

bais = new ByteArrayInputStream(baos.toByteArray());

InputStreamReader isr =

new InputStreamReader(bais);

BufferedReader br = new

BufferedReader(isr);

try {

header = new PacketHeader(br.readLine());

}

catch (Exception ex)

{

ex.printStackTrace();

}

}

private String calFileSize(int size)

{

return size / 1024 +

"K";

}

public ArrayList getDataPackets() {

return al;

}

public boolean isFull() {

return

this.header.getSn() == this.header.getFragmentcounter() - 1 ? true

: false;

}

public boolean isZero() {

return

this.header.getSn() == 0 ? true : false;

}

private ByteArrayOutputStream

fetchDataPackets() {

ByteArrayOutputStream

bos = new ByteArrayOutputStream();

byte[] buffer =

null;

DataEntry de;

for (int i = 0; i

< al.size(); i++) {

try

{

de = this.getSnData(i);

buffer = de.getByte();

if (header.getStreamsize() ==

de.getStreamsize()) {

bos.write(de.getByte(),

header.HEADER_BUFFER_SIZE, de.getActByteSize());

System.out.println(de.toString() + " -- fetchDataPackets");

}

}

catch

(Exception ex) {

ex.printStackTrace();

}

}

return bos;

}

private ByteArrayOutputStream

fetchDataPackets_sn() {

ByteArrayOutputStream

bos = new ByteArrayOutputStream();

byte[] buffer;

DataEntry de;

for (int i = 0; i

< header.getFragmentcounter(); i++) {

try

{

de = this.getSnData(i);

if (de == null) {

de = seachDeData(i);

}

buffer = de.getByte();

//System.out.println(de.getSn() + ":" +

i);

//handlerText(buffer);

//bos.write(buffer,

header.HEADER_BUFFER_SIZE,

//  buffer.length - header.HEADER_BUFFER_SIZE);

if (header.getStreamsize() ==

de.getStreamsize()) {

bos.write(de.getByte(),

header.HEADER_BUFFER_SIZE,

de.getActByteSize());

//System.out.println(de.toString());

}

}

catch

(Exception ex) {

ex.printStackTrace();

}

}

return bos;

}

private DataEntry getSnData(int sn) {

DataEntry de =

null;

for (int i = 0; i

< al.size(); i++) {

de =

(DataEntry) al.get(i);

if

(header.getStreamsize() == de.getStreamsize()) {

if (sn == de.getSn())

break;

else

de = null;

}

}

return de;

}

private DataEntry seachDeData(int sn)

{

DataEntry de =

null;

int initvalue, minvalue

= 10000;

DataEntry back, fore =

null;

for (int i = 0; i

< al.size(); i++) {

de =

(DataEntry) al.get(i);

if

(header.getStreamsize() == de.getStreamsize()) {

initvalue = Math.abs(de.getSn() - sn);

if (de.getFragmentcounter() != de.getSn()

&& initvalue <

minvalue) {

minvalue = initvalue;

fore = de;

}

}

}

return fore;

}

private DataEntry seachDeData() {

DataEntry de =

null;

for (int i = 0; i

< al.size(); i++) {

de =

(DataEntry) al.get(i);

System.out.println("sky ::::" + de.getFragmentcounter() + ":" +

de.getSn() +

":" + i);

if

(header.getStreamsize() == de.getStreamsize()) {

if (de.getFragmentcounter() != de.getSn())

{

break;

}

}

}

return de;

}

public java.awt.Image Gereratedata()

{

ByteArrayInputStream bis;

java.awt.image.BufferedImage bimage = null;

try

{

byte[] b =

fetchDataPackets_sn().toByteArray();

//fetchDataPackets_old1()

bis = new ByteArrayInputStream(b);

bimage = javax.imageio.ImageIO.read(bis);

}

catch

(Exception ex1) {

ex1.printStackTrace();

}

return

bimage;

}

public static void main(String args[])

{

DataPacket dp = new

DataPacket("e:\\nature\\14.jpg");

}

}

class DataEntry {

byte[] bytes;

int fragmentcounter, sn, actbytesize;

long streamsize;

int minfragment;

public DataEntry() {

}

public DataEntry(int size) {

this.actbytesize =

size;

}

public DataEntry(byte[] b, int i) {

this.bytes = b;

this.actbytesize =

i;

}

public byte[] getByte() {

return this.bytes;

}

public void setBytes(byte[] b) {

this.bytes = b;

}

public void setStreamsize(long size)

{

this.streamsize =

size;

}

public long getStreamsize() {

return

this.streamsize;

}

public int getMinfragment() {

return

minfragment;

}

public synchronized void setSn(int i)

{

this.sn = i;

}

public synchronized int getSn() {

return sn;

}

public synchronized int

getFragmentcounter() {

return

fragmentcounter;

}

public synchronized void

setFragmentcounter(int c) {

this.fragmentcounter =

c;

}

public void setActByteSize(int size)

{

actbytesize =

size;

}

public int getActByteSize() {

return

actbytesize;

}

public String toString() {

return this.streamsize +

"::" + this.fragmentcounter + "::" + this.sn +

"::" + this.actbytesize + " recv

DataEntry";

}

}

class PacketHeader implements Serializable{

public static final int HEADER_BUFFER_SIZE

= 1024;

int fragmentcounter, sn;

int actbytesize =

PacketBody.BODY_BUFFER_SIZE;

byte[] header; //= new

byte[HEADER_BUFFER_SIZE];

long streamsize;

int minfragment;

public PacketHeader() {

}

public PacketHeader(long l) {

this.setStreamsize(l);

}

public PacketHeader(String s) {

String[] tm =

s.split("::");

this.setActByteSize(Integer.parseInt(tm[3]));

this.setSn(Integer.parseInt(tm[2]));

this.setFragmentcounter(Integer.parseInt(tm[1]));

this.setStreamsize(Long.parseLong(tm[0]));

}

public void ArrageSort(int sn) {

this.setSn(sn);

this.setByte();

}

public void CalcHeaderInfo(long l) {

this.setStreamsize(l);

CalcHeaderInfo();

}

public void CalcHeaderInfo() {

fragmentcounter =

Math.round( (float) streamsize /

PacketBody.BODY_BUFFER_SIZE);

float critical = (float)

streamsize / PacketBody.BODY_BUFFER_SIZE;

if (critical -

fragmentcounter < 0.5

&& critical - fragmentcounter

> 0)

fragmentcounter++;

minfragment = (int)

(streamsize % PacketBody.BODY_BUFFER_SIZE);

}

public byte[] getHeader() {

Long it = new

Long(this.streamsize);

return new byte[]

{it.byteValue()};

}

public byte[] getByte() {

return header;

//this.toString().getBytes();

}

public void setByte() {

ByteArrayOutputStream

bos = new ByteArrayOutputStream();

byte[] buffer =

this.toByte();

try {

bos.write(buffer);

bos.write("\r\n".getBytes());

bos.write(new byte[PacketHeader.HEADER_BUFFER_SIZE -

buffer.length], 0,

PacketHeader.HEADER_BUFFER_SIZE - buffer.length);

header = bos.toByteArray();

}

catch (IOException ex)

{

ex.printStackTrace();

}

}

public void setStreamsize(long size)

{

this.streamsize =

size;

}

public long getStreamsize() {

return

this.streamsize;

}

public int getMinfragment() {

return

minfragment;

}

public synchronized void setSn(int i)

{

this.sn = i;

}

public int getSn() {

return sn;

}

public int getFragmentcounter() {

return

fragmentcounter;

}

public synchronized void

setFragmentcounter(int c) {

this.fragmentcounter =

c;

}

public void setActByteSize(int size)

{

actbytesize =

size;

setByte();

}

public int getActByteSize() {

return

actbytesize;

}

public String toString() {

return streamsize + "::"

+ this.fragmentcounter + "::" + this.getSn() +

"::" + this.getActByteSize();

}

public byte[] toByte() {

return

this.toString().getBytes();

}

public boolean isWTailFragment(int i)

{

return (i ==

fragmentcounter - 1) ? true : false;

}

}

class PacketBody implements Serializable{

public static final int BODY_BUFFER_SIZE =

63508; //65508

byte[] body;

public PacketBody() {

}

public void setBody(byte[] b) {

this.body = b;

}

public byte[] getBody() {

return body;

}

}