理解：模擬登陸指定網站，登陸成功後，獲取返回串中的cookie值用於發起下次請求。

package demo.http.client;

import java.io.IOException;
import java.io.InputStream;
import java.io.UnsupportedEncodingException;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.ArrayList;

public class JavaHttpClient {
	// common parameters
	private static String serverIP = "192.168.30.205";
	private static int serverPort = 80;
	private static String charset = "GBK";
	
	// login parameters
	private static String loginUrl = "/picp/SecurityAction.do?method=login";
	private static String loginNameIndex = "piUsersDto.usercode";// 使用者名稱索引
	private static String loginPwdIndex = "piUsersDto.password";// 密碼索引
	private static String loginName = "100001";//登陸使用者名稱
	private static String loginPwd = "111111";//登陸密碼
	private static String cookieIndex = "Set-Cookie: JSESSIONID=";//cookie索引串
	
	// check operation parameters
	private static String checkUrl="/picp/SingleInquireAction.do?method=query";
	private static String checkNameIndex="certname";//查詢名字索引
	private static String checkIdNumIndex="certno";//查詢證件號碼索引
	private static String checkType="businesscode";//查詢型別
	
	public static void main(String[] args) {
		JavaHttpClient obj=new JavaHttpClient();
		Socket clientSocket=null;
		try {
			clientSocket=new Socket(serverIP, serverPort);
			clientSocket.setSoTimeout(20*1000);
			//login
			String cookieValue=obj.login(clientSocket);
			if(cookieValue!=null){//check
				obj.checkOpt(clientSocket, cookieValue);
			}
		}catch (Exception e) {
			e.printStackTrace();
		}finally{
			if(clientSocket!=null){
				try {
					clientSocket.close();
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		}
		
	}

 

	/* 登陸操作，成功後返回cookie */
	private String login(Socket clientSocket) {
		String cookieValue=null;
		try {
			String loginStr=createLoginReqStr();
			clientSocket.getOutputStream().write(loginStr.getBytes(charset));
			clientSocket.getOutputStream().flush();
			String loginResponseStr=getResponseStr(clientSocket.getInputStream());
			//判斷是否登陸成功
			//end
			cookieValue=getCookieStr(loginResponseStr);
		}catch (Exception e) {
			e.printStackTrace();
		}
		return cookieValue;
	}
 

	/*組織登陸串*/
	private String createLoginReqStr() {
		try {
			String loginStr = loginNameIndex + "=" + loginName + "&"
					+ loginPwdIndex + "=" + loginPwd;
			StringBuffer sBuf = new StringBuffer();
			sBuf.append("POST " + loginUrl + " " + "HTTP/1.1\r\n");
			sBuf.append("Accept: "+ "text/html, application/xhtml+xml, */*\r\n");
			sBuf.append("Accept-Language: zh_CN\r\n");
			sBuf.append("Content-Type: application/x-www-form-urlencoded\r\n");
			sBuf.append("Host: " + serverIP + ":" + serverPort + "\r\n");
			sBuf.append("Content-Length: " + loginStr.getBytes(charset).length+"\r\n");
			sBuf.append("Connection: Keep-Alive\r\n");
			sBuf.append("Cache-Control: no-cache\r\n");
			sBuf.append("\r\n");
			sBuf.append(loginStr);
			return sBuf.toString();
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}
	
 

	/*查詢操作*/
	private void checkOpt(Socket clientSocket,String cookieValue){
		try {
			String checkStr=createCheckReqStr(cookieValue);
			clientSocket.getOutputStream().write(checkStr.getBytes(charset));
			clientSocket.getOutputStream().flush();
			String checkResponseStr=getResponseStr(clientSocket.getInputStream());
		} catch (Exception e) {
			e.printStackTrace();
		}
		
	}
	

	/*組織查詢串*/
	private String createCheckReqStr(String cookieValue) {
		StringBuffer sBuf=new StringBuffer();
		try {
			String checkStr=checkType+"="+"01&"+checkNameIndex+"="+"熊大"+"&"+checkIdNumIndex+"="+"370785198910047763";
			for(int i=1;i<5;i++){
				checkStr=checkStr+"&"+checkNameIndex+"=&"+checkIdNumIndex+"=";
			}
			sBuf.append("POST " + checkUrl + " " + "HTTP/1.1\r\n");
			sBuf.append("Accept: "+ "text/html, application/xhtml+xml, */*\r\n");
			sBuf.append("Accept-Language: zh_CN\r\n");
			sBuf.append("Content-Type: application/x-www-form-urlencoded\r\n");
			sBuf.append("Host: " + serverIP + ":" + serverPort + "\r\n");
			sBuf.append("Content-Length: " + checkStr.getBytes(charset).length+"\r\n");
			sBuf.append("Connection: Keep-Alive\r\n");
			sBuf.append("Cache-Control: no-cache\r\n");
			sBuf.append("Cookie: JSESSIONID="+cookieValue+"\r\n");
			sBuf.append("\r\n");
			sBuf.append(checkStr);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return sBuf.toString();
	}
	

	/*獲取返回值*/
	private String getResponseStr(InputStream ins){
		StringBuffer sBuf=new StringBuffer();
		int contentLength=0;//儲存http header中contentLength的值
		try {
			String aLine=null;
			do{
				aLine=readFromStream(ins, 0);
				if(aLine.contains("Content-Length")){
					contentLength=Integer.parseInt(aLine.split(":")[1].trim());
				}
				sBuf.append(aLine);
			}while(!aLine.equals("\r\n"));
			sBuf.append(readFromStream(ins, contentLength));
		} catch (Exception e) {
			e.printStackTrace();
		}
		return sBuf.toString();
	}

	/* 從流中讀取指定長度的位元組，readLenth為0時，讀取一行 */
	private String readFromStream(InputStream ins, int readLength) {
		try {
			byte tmpB;
			byte[] byteArr;
			if (readLength == 0) {// 讀取一行
				ArrayList byteList = new ArrayList();
				do {
					tmpB = (byte) ins.read();
					byteList.add(tmpB);
				} while (tmpB != 10);// 判斷是否換行
				byteArr = new byte[byteList.size()];
				for (int i = 0; i < byteList.size(); i++) {
					byteArr[i] = (Byte) byteList.get(i);
				}
				byteList.clear();
			} else {// 讀取指定長度
				int index = 0;
				byteArr = new byte[readLength];
				do {
					byteArr[index] = (byte) ins.read();
					index++;
				} while (index < readLength);
			}
			return new String(byteArr, charset);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}
	

	/*獲取cookie值*/
	private String getCookieStr(String loginResponseStr){
		String cookieValue=null;
		try {
			int index=loginResponseStr.indexOf(cookieIndex);
			System.out.println(index);
			if(index>-1){
				cookieValue = loginResponseStr.substring(index + 23, index + 55);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}	
		return cookieValue;
	}
}