Good day, an error occurs when you start the app:
03-09 16:51:36.537 24639-24639/? E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.webserver, PID: 24639 java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.webserver/com.example.webserver.MainActivity}: java.lang.InstantiationException: java.lang.Class has no zero argument constructor at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2515) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2670) at android.app.ActivityThread.access$1100(ActivityThread.java:178) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1515) at android.os.Handler.dispatchMessage(Handler.java:111) at android.os.Looper.loop(Looper.java:207) at android.app.ActivityThread.main(ActivityThread.java:5845) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:907) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:768) Caused by: java.lang.InstantiationException: java.lang.Class has no zero argument constructor at java.lang.Class.newInstance(Native Method) at android.app.Instrumentation.newActivity(Instrumentation.java:1072) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2505)
I'm trying to make a web server on Android. Here's the code:
package com.example.webserver;
import androidx.appcompat.app.AppCompatActivity;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Date;
import java.util.StringTokenizer;
// The tutorial can be found just here on the SSaurel's Blog :
// https://www.ssaurel.com/blog/create-a-simple-http-web-server-in-java
// Each Client Connection will be managed in a dedicated Thread
public class MainActivity implements Runnable {
static final File WEB_ROOT = new File(".");
static final String DEFAULT_FILE = "index.html";
static final String FILE_NOT_FOUND = "404.html";
static final String METHOD_NOT_SUPPORTED = "not_supported.html";
// port to listen connection
static final int PORT = 8080;
// verbose mode
static final boolean verbose = true;
// Client Connection via Socket Class
private Socket connect;
public MainActivity(Socket c) {
connect = c;
}
public static void main(String[] args) {
try {
ServerSocket serverConnect = new ServerSocket(PORT);
System.out.println("Server started.\nListening for connections on port : " + PORT + " ...\n");
// we listen until user halts server execution
while (true) {
MainActivity myServer = new MainActivity(serverConnect.accept());
if (verbose) {
System.out.println("Connecton opened. (" + new Date() + ")");
}
// create dedicated thread to manage the client connection
Thread thread = new Thread(myServer);
thread.start();
}
} catch (IOException e) {
System.err.println("Server Connection error : " + e.getMessage());
}
}
@Override
public void run() {
// we manage our particular client connection
BufferedReader in = null; PrintWriter out = null; BufferedOutputStream dataOut = null;
String fileRequested = null;
try {
// we read characters from the client via input stream on the socket
in = new BufferedReader(new InputStreamReader(connect.getInputStream()));
// we get character output stream to client (for headers)
out = new PrintWriter(connect.getOutputStream());
// get binary output stream to client (for requested data)
dataOut = new BufferedOutputStream(connect.getOutputStream());
// get first line of the request from the client
String input = in.readLine();
// we parse the request with a string tokenizer
StringTokenizer parse = new StringTokenizer(input);
String method = parse.nextToken().toUpperCase(); // we get the HTTP method of the client
// we get file requested
fileRequested = parse.nextToken().toLowerCase();
// we support only GET and HEAD methods, we check
if (!method.equals("GET") && !method.equals("HEAD")) {
if (verbose) {
System.out.println("501 Not Implemented : " + method + " method.");
}
// we return the not supported file to the client
File file = new File(WEB_ROOT, METHOD_NOT_SUPPORTED);
int fileLength = (int) file.length();
String contentMimeType = "text/html";
//read content to return to client
byte[] fileData = readFileData(file, fileLength);
// we send HTTP Headers with data to client
out.println("HTTP/1.1 501 Not Implemented");
out.println("Server: Java HTTP Server from SSaurel : 1.0");
out.println("Date: " + new Date());
out.println("Content-type: " + contentMimeType);
out.println("Content-length: " + fileLength);
out.println(); // blank line between headers and content, very important !
out.flush(); // flush character output stream buffer
// file
dataOut.write(fileData, 0, fileLength);
dataOut.flush();
} else {
// GET or HEAD method
if (fileRequested.endsWith("/")) {
fileRequested += DEFAULT_FILE;
}
File file = new File(WEB_ROOT, fileRequested);
int fileLength = (int) file.length();
String content = getContentType(fileRequested);
if (method.equals("GET")) { // GET method so we return content
byte[] fileData = readFileData(file, fileLength);
// send HTTP Headers
out.println("HTTP/1.1 200 OK");
out.println("Server: Java HTTP Server from SSaurel : 1.0");
out.println("Date: " + new Date());
out.println("Content-type: " + content);
out.println("Content-length: " + fileLength);
out.println(); // blank line between headers and content, very important !
out.flush(); // flush character output stream buffer
dataOut.write(fileData, 0, fileLength);
dataOut.flush();
}
if (verbose) {
System.out.println("File " + fileRequested + " of type " + content + " returned");
}
}
} catch (FileNotFoundException fnfe) {
try {
fileNotFound(out, dataOut, fileRequested);
} catch (IOException ioe) {
System.err.println("Error with file not found exception : " + ioe.getMessage());
}
} catch (IOException ioe) {
System.err.println("Server error : " + ioe);
} finally {
try {
in.close();
out.close();
dataOut.close();
connect.close(); // we close socket connection
} catch (Exception e) {
System.err.println("Error closing stream : " + e.getMessage());
}
if (verbose) {
System.out.println("Connection closed.\n");
}
}
}
private byte[] readFileData(File file, int fileLength) throws IOException {
FileInputStream fileIn = null;
byte[] fileData = new byte[fileLength];
try {
fileIn = new FileInputStream(file);
fileIn.read(fileData);
} finally {
if (fileIn != null)
fileIn.close();
}
return fileData;
}
// return supported MIME Types
private String getContentType(String fileRequested) {
if (fileRequested.endsWith(".htm") || fileRequested.endsWith(".html"))
return "text/html";
else
return "text/plain";
}
private void fileNotFound(PrintWriter out, OutputStream dataOut, String fileRequested) throws IOException {
File file = new File(WEB_ROOT, FILE_NOT_FOUND);
int fileLength = (int) file.length();
String content = "text/html";
byte[] fileData = readFileData(file, fileLength);
out.println("HTTP/1.1 404 File Not Found");
out.println("Server: Java HTTP Server from SSaurel : 1.0");
out.println("Date: " + new Date());
out.println("Content-type: " + content);
out.println("Content-length: " + fileLength);
out.println(); // blank line between headers and content, very important !
out.flush(); // flush character output stream buffer
dataOut.write(fileData, 0, fileLength);
dataOut.flush();
if (verbose) {
System.out.println("File " + fileRequested + " not found");
}
}
}
