我在端口6799上运行我的java webserver 我的目录有一个txt.txt文件和pdf.pdf文件 当我给localhost:6799 / txt.txt时,它提供了完美的输出
GET /txt.txt HTTP / 1.1HTTP / 1.0 200 OK 内容类型:text / plain
这是一个非常简单的文本文件
但是当我从浏览器给出localhost:6799 / pdf.pdf时,它会给出java.lang.NullPointerException
这是我的代码
import java.net.*;
public final class WebServer {
public static void main(String args[]) throws Exception {
int port = 6799;
System.out.println("\nListening on port " + port);
ServerSocket listen = new ServerSocket(port);
while (true) {
Socket socket = listen.accept();
HttpRequest request = new HttpRequest(socket);
Thread thread = new Thread(request);
thread.start();
}
}
}
-
import java.io.*;
import java.net.*;
import java.util.StringTokenizer;
public final class HttpRequest implements Runnable {
final String CRLF = "\r\n";
Socket socket;
public HttpRequest(Socket socket) throws Exception {
this.socket = socket;
}
@Override
public void run() {
try {
processRequest();
} catch (Exception e) {
System.out.println(e);
}
}
private void processRequest() throws Exception {
BufferedReader br;
DataOutputStream dos;
try (InputStream is = socket.getInputStream()) {
br = new BufferedReader(new InputStreamReader(is));
String requestline = br.readLine();
System.out.println("\n" + requestline);
String headerLine = null;
while ((headerLine = br.readLine()).length() != 0) {
System.out.println(headerLine);
}
dos = new DataOutputStream(socket.getOutputStream());
dos.writeBytes(requestline);
StringTokenizer tokens = new StringTokenizer(requestline);
tokens.nextToken(); // skip over the method, which should be "GET"
String fileName = tokens.nextToken();
// Prepend a "." so that file request is within the current directory.
fileName = "." + fileName;
FileInputStream fis = null;
boolean fileExists = true;
try {
fis = new FileInputStream(fileName);
} catch (FileNotFoundException e) {
fileExists = false;
}
String statusLine = null;
String contentTypeLine = null;
String entityBody = null;
if (fileExists) {
statusLine = "HTTP/1.0 200 OK" + CRLF;
contentTypeLine = "Content-type: " + contentType(fileName) + CRLF;
} else {
statusLine = "HTTP/1.0 404 Not Found" + CRLF;
//contentTypeLine = "Content-type: " + "text/html" + CRLF;
entityBody = "<HTML>"
+ "<HEAD><TITLE>Not Found</TITLE></HEAD>"
+ "<BODY>Not Found</BODY></HTML>";
}
dos.writeBytes(statusLine);
dos.writeBytes(contentTypeLine);
dos.writeBytes(CRLF);
if (fileExists) {
sendBytes(fis, dos);
fis.close();
} else {
dos.writeBytes(entityBody);
}
}
br.close();
dos.close();
socket.close();
}
private void sendBytes(FileInputStream fis, DataOutputStream dos) throws IOException {
byte[] buffer = new byte[4096];
int bytes = 0;
while ((bytes = fis.read(buffer)) != -1) {
dos.write(buffer, 0, bytes);
}
}
private String contentType(String fileName) {
if (fileName.endsWith(".htm") || fileName.endsWith(".html")) {
return "text/html";
}
if (fileName.endsWith(".jpg") || fileName.endsWith(".jpeg")) {
return "image/jpeg";
}
if (fileName.endsWith(".gif")) {
return "image/gif";
}
if (fileName.endsWith(".txt")) {
return "text/plain";
}
if (fileName.endsWith(".pdf")) {
return "application/pdf";
}
return "application/octet-stream";
}
}
STACK TRACE
java.lang.NullPointerException
at java.io.DataOutputStream.writeBytes(DataOutputStream.java:274)
at HttpRequest.processRequest(HttpRequest.java:65)
at HttpRequest.run(HttpRequest.java:20)
at java.lang.Thread.run(Thread.java:724)
答案 0 :(得分:0)
此代码至少有一个问题:
while ((headerLine = br.readLine()).length() != 0) {
System.out.println(headerLine);
}
BufferedReader
将在流的末尾返回null
,因此在空对象上调用.length()
将产生NullPointerException
。
更为惯用的方法是:
while ((headerLine = br.readLine()) != null && headerLine.length() != 0) {
System.out.println(headerLine);
}
...如果(headerLine = br.readLine())
的结果为null
,则利用短路逻辑不评估第二个条件。
答案 1 :(得分:0)
这种情况正在发生,因为出于某种原因,您已在以下一行切换评论:
//contentTypeLine = "Content-type: " + "text/html" + CRLF;
解开它,你很好!