我有一个简单的 UDP 服务器和客户端。服务器使用该readInDataFile() 方法用文本文件中的所有字符串填充数组列表。我的服务器可以轻松地从字节中读取字符串 "dis.readUTF(); "extracted = dis.readUTF();"
，我的客户端可以轻松地使用dis.writeUTF();
我遵循相同的结构和逻辑将从数组中找到的字符串发送到客户端，但它没有收到任何内容。
*我的问题：为什么客户端没有正确读取字符串？我知道服务器正在正确读取年份，因为我有一个打印语句来使用发送的字符串并进入 arrayList 以确定我们要打印的内容。
我正在读取的 .txt 文件的字符串从 1875 开始一直到 2011 年，因此如果客户端输入“2011”，它将传递给服务器，服务器将进入 .txt 文件并检索“2011”动物王国约翰·委拉斯开兹 2:02.04"
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.SocketTimeoutException;
import java.net.UnknownHostException;
import java.util.Scanner;
public class DerbyUDPClient {
public InetAddress ip = null;
// To print the string at the end
String finalPrint = "";
// Socket for UDP communication with server
DatagramSocket dgs = null;
DatagramSocket dgs2 = null;
// The DataGramPacket used with server
DatagramPacket dgp = null;
DatagramPacket dgp2 = null;
ByteArrayOutputStream bos = null;
DataOutputStream dos = null;
String year = "";
// The String to hold the user's IP Address
String ipString = "";
Scanner input = new Scanner(System.in);
public DerbyUDPClient() throws IOException {
getIPAddressServerAndYear();
}
public void getIPAddressServerAndYear() throws IOException {
// Ask user for IP address, or they can just press return
System.out.println("Enter the IP Address of the server, please: ");
ipString = input.nextLine();
if (ipString.length() == 0) {
ipString = "127.0.0.1";
}
try {
ip = InetAddress.getByName(ipString);
} catch (UnknownHostException e) {
e.printStackTrace();
}
// Ask user for IP address, or they can just press return
System.out.println("Please enter a year between 1875 and 2011: ");
year = input.nextLine();
// Checks to see if the user has inputed a year
if (isInteger(year) == true) {
// write and then receive
dgs = new DatagramSocket();
bos = new ByteArrayOutputStream();
dos = new DataOutputStream(bos);
dos.writeUTF(year);
dgp = new DatagramPacket(bos.toByteArray(), bos.size());
dgp.setAddress(InetAddress.getLocalHost());
dgp.setPort(28150);
dgs.send(dgp);
// receive
dgs.receive(dgp);
ByteArrayInputStream bis = new ByteArrayInputStream(dgp.getData());
DataInputStream dis = new DataInputStream(bis);
finalPrint = dis.readUTF();
System.out.println(finalPrint);
dgs.close();
}
}
public boolean isInteger(String input) {
try {
Integer.parseInt(input);
return true;
} catch (Exception e) {
return false;
}
}
public static void main(String[] args) throws IOException {
new DerbyUDPClient();
} // end main
} // end DerbyUDPClient
<><><><><><><><><><><><><><><><><><><><><><>><>><><><><>><><><> New class below
import java.io.BufferedReader;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;
import java.net.UnknownHostException;
import java.util.ArrayList;
public class DerbyUDPServer {
// Socket for UDP communication with clients
DatagramSocket dgs = null;
DatagramSocket dgs2 = null;
// The DataGramPacket used
DatagramPacket dgp = null;
ByteArrayInputStream bis = null;
DataInputStream dis = new DataInputStream(bis);
int clientPort = 0;
DatagramPacket dgp2 = null;
// The string converted to an int is held in this variable
int parsedString = 0;
// Flag set to false when server should close
boolean listening = true;
// The String that is used to hold the extracted String
String extracted = "";
// Total number of clients server has sent data to
int clientCount = 0;
// Port number that server listens on
static final int SERVER_PORT = 31250;
ByteArrayOutputStream bos = null;
DataOutputStream dos = null;
// Array list containing a list of strings describing
// Kentucky derby winners
ArrayList<String> winners = new ArrayList<String>();
public DerbyUDPServer() throws IOException {
readInDataFile();
handleClients();
} // end DerbyUDPServer constructor
protected void readInDataFile() throws IOException {
int winIdx = 0;
String singleWinner;
BufferedReader in = new BufferedReader(new FileReader("derby.txt"));
while ((singleWinner = in.readLine()) != null) {
winners.add(singleWinner);
winIdx++;
}
in.close();
} // end readInDataFile
/*
* Displays IP address and port number that clients can use to contact the
* server to the console.
*/
protected void displayContactInfo() {
try {
// Display contact information.
System.out.println("Number Server standing by to accept Clients:"
+ "\nIP : " + InetAddress.getLocalHost() + "\nPort: "
+ dgs.getLocalPort() + "\n\n");
} catch (UnknownHostException e) {
// NS lookup for host IP failed?
// This should only happen if the host machine does
// not have an IP address.
e.printStackTrace();
}
} // end displayContactInfo
public void handleClients() throws IOException {
try {
dgs = new DatagramSocket(28150);
dgp = new DatagramPacket(new byte[50], 50);
} catch (SocketException e) {
e.printStackTrace();
}
displayContactInfo();
// Receive and then write
// receive here
dgs.receive(dgp);
// Prints out the IP address and Port of the DataGramPacket
System.out.println(dgp.getAddress());
System.out.println(dgp.getPort());
// Extract the string from the bytes
ByteArrayInputStream bis = new ByteArrayInputStream(dgp.getData());
DataInputStream dis = new DataInputStream(bis);
// Read in the string from the DataInputString...
try {
extracted = dis.readUTF();
} catch (IOException e) {
e.printStackTrace();
}
// System.out.println("You entered the year: " + extracted);
// Converts the String to an integer
parsedString = Integer.parseInt(extracted);
// This below prints, so I am obviously receiving the integer year from the client
System.out.println(getYearLine(parsedString));
// Write below
bos = new ByteArrayOutputStream();
dos = new DataOutputStream(bos);
dos.writeUTF(getYearLine(parsedString));
dgp2 = new DatagramPacket(bos.toByteArray(), bos.size());
dgp2.setAddress(dgp.getAddress());
dgp2.setPort(dgp.getPort());
dgs.send(dgp2);
while(listening == true){
handleClients();
}
}
public String getYearLine(int year) {
if (year < 2012 && year > 1874) {
return winners.get(2011 - year);
} else {
return "no derby info for that year";
}
} // getYearLine
public static void main(String[] args) throws IOException {
new DerbyUDPServer();
} // end main
} // end DerbyUDPServer