梁穎健
liangyingjian@21cn.com Http用戶端程式已整合在Java語言中，可以通過URLConnection類調用。遺憾的
是，由於SUN沒有公布Http客戶程式的源碼，它實現的細節仍是一個謎。本文根據HTTP
協議規範，用Java.net.Socket類實現一個HTTP協議用戶端程式。 1.Socket類:
瞭解TCP/IP協議集通訊的讀者知道，協議間的通訊是通過Socket完成的。在
Java.net包中，Socket類就是對Socket的具體實現。它通過串連到主機後，返回一個
I/O流，實現協議間的資訊交換。 2 . HTTP協議
HTTP協議同其它TCP/IP協議集中的協議一樣，是遵循客戶/伺服器模型工作的。客
戶端發往服務端的資訊格式如下:
------------------------------
要求方法 URL HTTP協議的版本號碼
提交的元資訊
**空行**
實體
------------------------------
要求方法是對這次串連工作的說明，目前HTTP協議已經發展到1.1版，它包括GET、
HEAD、POST、DELETE、OPTIONS、TRACE、PUT七種。元資訊是關於當前請求的資訊。通
過分析元資訊，可以檢查實體資料是否完整，接收過程是否出錯，類型是否匹配等。元
資訊的引入使HTTP協議通訊更加穩妥可靠。實體是請求的具體內容。
將上述報文發往Web伺服器，如果成功，應答格式如下:
--------------------------------
HTTP協議的版本號碼 應答狀態代碼 應答狀態代碼說明
接收的元資訊
**空行**
實體
--------------------------------
以上報文發向用戶端，並且接收成功，彼此間關閉串連，完成一次握手。
下面用最常用的GET方法，來說明具體的報文應用
----------------------------------
GET http://www.youhost.com HTTP/1.0
accept: www/source; text/html; image/gif; image/jpeg; */*
User_Agent: myAgent
**空行**
-----------------------------------
這個報文是向www.youhost.com主機請求一個預設HTML文檔。用戶端HTTP協議版本
號是1.0版，元資訊包括可接收的檔案格式，使用者代理程式，每一段之間用斷行符號分行符號分
隔，最後以一個空行結束。發向伺服器後，如果執行過程正常，伺服器返回以下代碼:
------------------------------------
HTTP/1.1 200 OK
Date: Tue, 14 Sep 1999 02:19:57 GMT
Server: Apache/1.2.6
Connection: close
Content-Type: text/html
**空行**
<html><head>...</head><body>...</body></html>
------------------------------------
HTTP/1.1表示這個HTTP伺服器是1.1版，200是伺服器對客戶請求的應答狀態代碼，OK
是對應答狀態代碼的解釋，之後是這個文檔的元資訊和文檔本文。(相關應答狀態代碼和元
資訊的解釋請參閱Inetrnet標準草案:RFC2616)。 3. HTTP用戶端程式: import java.net.*;
import java.io.*;
import java.util.Properties;
import java.util.Enumeration;
public class Http {
protected Socket client;
protected BufferedOutputStream sender;
protected BufferedInputStream receiver;
protected ByteArrayInputStream byteStream;
protected URL target;
private int responseCode=-1;
private String responseMessage="";
private String serverVersion="";
private Properties header = new Properties();
public Http() { }
public Http(String url) {
GET(url) ;
}
/* GET方法根據URL，會請求檔案、資料庫查詢結果、程式運行結果等多種內容 */
public void GET(String url) {
try {
checkHTTP(url);
openServer(target.getHost(),target.getPort() );
String cmd = "GET "+ getURLFormat(target) +" HTTP/1.0/r/n"
+ getBaseHeads()+"/r/n";
sendMessage(cmd);
receiveMessage();
}catch(ProtocolException p) {
p.printStackTrace();
return;
}catch(UnknownHostException e) {
e.printStackTrace();
return;
}catch(IOException i) i.printStackTrace();
return;
}
} /*
* HEAD方法只請求URL的元資訊，不包括URL本身。若懷疑本機和伺服器上的
* 檔案相同，用這個方法檢查最快捷有效。
*/
public void HEAD(String url) {
try {
checkHTTP(url);
openServer(target.getHost(),target.getPort() );
String cmd = "HEAD "+getURLFormat(target)+" HTTP/1.0/r/n"
+getBaseHeads()+"/r/n";
sendMessage(cmd);
receiveMessage();
}catch(ProtocolException p) {
p.printStackTrace();
return;
}catch(UnknownHostException e) {
e.printStackTrace();
return;
}catch(IOException i) i.printStackTrace();
return;
}
}
/*
* POST方法是向伺服器傳送資料，以便伺服器做出相應的處理。例如網頁上常用的
* 提交表格。
*/
public void POST(String url,String content) {
try {
checkHTTP(url);
openServer(target.getHost(),target.getPort() );
String cmd = "POST "+ getURLFormat(target) +"
HTTP/1.0/r/n"+getBaseHeads();
cmd += "Content-type: application/x-www-form-urlencoded/r/n";
cmd += "Content-length: " + content.length() + "/r/n/r/n";
cmd += content+"/r/n";
sendMessage(cmd);
receiveMessage();
}catch(ProtocolException p) {
p.printStackTrace();
return;
}catch(UnknownHostException e) {
e.printStackTrace();
return;
}catch(IOException i) i.printStackTrace();
return;
} }
protected void checkHTTP(String url) throws ProtocolException {
try {
URL target = new URL(url);
if(target==null || !target.getProtocol().toUpperCase().equals("HTTP") )
throw new ProtocolException("這不是HTTP協議");
this.target = target;
}catch(MalformedURLException m) {
throw new ProtocolException("協議格式錯誤");
}
}
/*
* 與Web伺服器串連。若找不到Web伺服器，InetAddress會引發UnknownHostException
* 異常。若Socket串連失敗，會引發IOException異常。
*/
protected void openServer(String host,int port) throws
UnknownHostException,IOException {
header.clear();
responseMessage=""; responseCode=-1;
try {
if(client!=null) closeServer();
if(byteStream != null) {
byteStream.close(); byteStream=null;
}
InetAddress address = InetAddress.getByName(host);
client = new Socket(address,port==-1?80:port);
sender = new BufferedOutputStream(client.getOutputStream());
receiver = new BufferedInputStream(client.getInputStream());
}catch(UnknownHostException u) {
throw u;
}catch(IOException i) {
throw i;
}
}
/* 關閉與Web伺服器的串連 */
protected void closeServer() throws IOException {
if(client==null) return;
try {
client.close(); sender.close(); receiver.close();
}catch(IOException i) {
throw i;
}
client=null; sender=null; receiver=null;
}
protected String getURLFormat(URL target) {
String spec = "http://"+target.getHost();
if(target.getPort()!=-1)
spec+=":"+target.getPort();
return spec+=target.getFile();
} /* 向Web伺服器傳送資料 */
protected void sendMessage(String data) throws IOException{
sender.write(data.getBytes(),0,data.length());
sender.flush();
}
/* 接收來自Web伺服器的資料 */
protected void receiveMessage() throws IOException{
byte data[] = new byte[1024];
int count=0;
int word=-1;
// 解析第一行
while( (word=receiver.read())!=-1 ) {
if(word=='/r'||word=='/n') {
word=receiver.read();
if(word=='/n') word=receiver.read();
break;
}
if(count == data.length) data = addCapacity(data);
data[count++]=(byte)word;
}
String message = new String(data,0,count);
int mark = message.indexOf(32);
serverVersion = message.substring(0,mark);
while( mark<message.length() && message.charAt(mark+1)==32 ) mark++;
responseCode = Integer.parseInt(message.substring(mark+1,mark+=4));
responseMessage = message.substring(mark,message.length()).trim(); // 應答狀態代碼和處理請讀者添加
switch(responseCode) {
case 400:
throw new IOException("錯誤請求");
case 404:
throw new FileNotFoundException( getURLFormat(target) );
case 503:
throw new IOException("伺服器不可用" );
}
if(word==-1) throw new ProtocolException("資訊接收異常終止");
int symbol=-1;
count=0;
// 解析元資訊
while( word!='/r' && word!='/n' && word>-1) {
if(word=='/t') word=32;
if(count==data.length) data = addCapacity(data);
data[count++] = (byte)word;
parseLine: {
while( (symbol=receiver.read()) >-1 ) {
switch(symbol) {
case '/t':
symbol=32; break;
case '/r':
case '/n':
word = receiver.read();
if( symbol=='/r' && word=='/n') {
word=receiver.read();
if(word=='/r') word=receiver.read();
}
if( word=='/r' || word=='/n' || word>32) break parseLine;
symbol=32; break;
}
if(count==data.length) data = addCapacity(data);
data[count++] = (byte)symbol;
}
word=-1;
}
message = new String(data,0,count);
mark = message.indexOf(':');
String key = null;
if(mark>0) key = message.substring(0,mark);
mark++;
while( mark<message.length() && message.charAt(mark)<=32 ) mark++;
String value = message.substring(mark,message.length() );
header.put(key,value);
count=0;
}
// 獲得本文資料
while( (word=receiver.read())!=-1) {
if(count == data.length) data = addCapacity(data);
data[count++] = (byte)word;
}
if(count>0) byteStream = new ByteArrayInputStream(data,0,count);
data=null;
closeServer();
}
public String getResponseMessage() {
return responseMessage;
}
public int getResponseCode() {
return responseCode;
}
public String getServerVersion() {
return serverVersion;
}
public InputStream getInputStream() {
return byteStream;
}
public synchronized String getHeaderKey(int i) {
if(i>=header.size()) return null;
Enumeration enum = header.propertyNames();
String key = null;
for(int j=0; j<=i; j++)
key = (String)enum.nextElement();
return key;
}
public synchronized String getHeaderValue(int i) {
if(i>=header.size()) return null;
return header.getProperty(getHeaderKey(i));
}
public synchronized String getHeaderValue(String key) {
return header.getProperty(key);
}
protected String getBaseHeads() {
String inf = "User-Agent: myselfHttp/1.0/r/n"+
"Accept: www/source; text/html; image/gif; */*/r/n";
return inf;
}
private byte[] addCapacity(byte rece[]){
byte temp[] = new byte[rece.length+1024];
System.arraycopy(rece,0,temp,0,rece.length);
return temp;
}
} 注: 程式中只實現GET、HEAD、POST三種方法。其他幾種因不常使用，暫且忽略。 |
