分类：
2008-10-17 13:49:02
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，但在大型上却会出现错误。
UDP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;
/**
* 在接收数据报使用
*/
public DataPacket() {
header = new PacketHeader();
body = new PacketBody();
al = new ArrayList();
}
/**
* 在发送数据报时使用,它调用报文分割操作.
* @param file String 硬盘文件
*/
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();
}
}
/**
* 在发送数据报时使用,它调用报文分割操作.
* @param url URL url地址
*/
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();
}
}
/**
* 为发送构造分组,使用PackageHeader处理了报头格式,并为分组编序号.
*/
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();
}
}
}
/**
* 为发送构造分组,没有考虑报头格式,也没有为分组编序号.
*/
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();
}
}
}
/**
* 在接收到报文后,对此报文执行组装,并处理报文丢失和乱序情况.
* @param b1 byte[]
*/
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;
}
/**
* 是否接收完毕,通过序号是否等于最大段数来判断,这也许有问题,比如,正好是最后一个段丢失了,这样
* 这个包整个就丢失了.
* @return
*/
public boolean isFull() {
return this.header.getSn() == this.header.getFragmentcounter() - 1 ? true : false;
}
/**
* 判断是否只有一个段.
* @return
*/
public boolean isZero() {
return this.header.getSn() == 0 ? true : false;
}
/**
* 该函数执行报文组装,不考虑丢失的报文.
* @return
*/
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;
}
/**
* 该函数执行报文组装,对于丢失的报文,写入空报文.
* @return ByteArrayOutputStream
*/
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;
}
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