[英]Connect android client with c server in linux
我必须创建一个简单的 android 应用程序,它与 c 中的服务器通信,仅使用 java Z222089455 库。 I wrote this server in c on a linux virtual machine and the application using android studio on windows but it seems that this does not connect to the server
客户端.java
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import androidx.appcompat.app.AppCompatActivity;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
public class MainActivity extends AppCompatActivity {
private Socket socket;
private static final int SERVERPORT = 8888;
private static final String SERVER_IP = "10.0.2.15";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new Thread(new ClientThread()).start();
}
public void onClick(View view) {
try {
EditText et = findViewById(R.id.EditText01);
String str = et.getText().toString();
PrintWriter out = new PrintWriter(new BufferedWriter(
new OutputStreamWriter(socket.getOutputStream())),
true);
out.println(str);
} catch (Exception e) {
e.printStackTrace();
}
}
class ClientThread implements Runnable {
@Override
public void run() {
try {
InetAddress serverAddr = InetAddress.getByName(SERVER_IP);
socket = new Socket(serverAddr, SERVERPORT);
} catch (IOException e1) {
e1.printStackTrace();
}
}
}
}
服务器.c
/*
C socket server example
*/
#include<stdio.h>
#include<string.h> //strlen
#include<sys/socket.h>
#include<arpa/inet.h> //inet_addr
#include<unistd.h> //write
int main(int argc , char *argv[])
{
int socket_desc , client_sock , c , read_size;
struct sockaddr_in server , client;
char client_message[2000];
//Create socket
socket_desc = socket(AF_INET , SOCK_STREAM , 0);
if (socket_desc == -1)
{
printf("Could not create socket");
}
puts("Socket created");
//Prepare the sockaddr_in structure
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons( 8888 );
//Bind
if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
{
//print the error message
perror("bind failed. Error");
return 1;
}
puts("bind done");
//Listen
listen(socket_desc , 3);
//Accept and incoming connection
puts("Waiting for incoming connections...");
c = sizeof(struct sockaddr_in);
//accept connection from an incoming client
client_sock = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c);
if (client_sock < 0)
{
perror("accept failed");
return 1;
}
puts("Connection accepted");
//Receive a message from client
while( (read_size = recv(client_sock , client_message , 2000 , 0)) > 0 )
{
//Send the message back to client
write(client_sock , client_message , strlen(client_message));
}
if(read_size == 0)
{
puts("Client disconnected");
fflush(stdout);
}
else if(read_size == -1)
{
perror("recv failed");
}
return 0;
}
当我尝试通过按下按钮发送消息时,这是 logcat:
2021-04-27 08:34:40.858 1185-1185/com.example.androdi_socket_example W/System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.OutputStream java.net.Socket.getOutputStream()' on a null object reference
2021-04-27 08:34:40.859 1185-1185/com.example.androdi_socket_example W/System.err: at com.example.androdi_socket_example.MainActivity.onClick(MainActivity.java:36)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at java.lang.reflect.Method.invoke(Native Method)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:409)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at android.view.View.performClick(View.java:6294)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at android.view.View$PerformClick.run(View.java:24770)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at android.os.Handler.handleCallback(Handler.java:790)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at android.os.Handler.dispatchMessage(Handler.java:99)
2021-04-27 08:34:40.861 1185-1185/com.example.androdi_socket_example W/System.err: at android.os.Looper.loop(Looper.java:164)
2021-04-27 08:34:40.861 1185-1185/com.example.androdi_socket_example W/System.err: at android.app.ActivityThread.main(ActivityThread.java:6494)
2021-04-27 08:34:40.861 1185-1185/com.example.androdi_socket_example W/System.err: at java.lang.reflect.Method.invoke(Native Method)
2021-04-27 08:34:40.861 1185-1185/com.example.androdi_socket_example W/System.err: at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
2021-04-27 08:34:40.861 1185-1185/com.example.androdi_socket_example W/System.err: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
我必须创建一个简单的 android 应用程序,它与 c 中的服务器通信,仅使用 java Z222089455 库。 I wrote this server in c on a linux virtual machine and the application using android studio on windows but it seems that this does not connect to the server
客户端.java
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import androidx.appcompat.app.AppCompatActivity;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
public class MainActivity extends AppCompatActivity {
private Socket socket;
private static final int SERVERPORT = 8888;
private static final String SERVER_IP = "10.0.2.15";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
new Thread(new ClientThread()).start();
}
public void onClick(View view) {
try {
EditText et = findViewById(R.id.EditText01);
String str = et.getText().toString();
PrintWriter out = new PrintWriter(new BufferedWriter(
new OutputStreamWriter(socket.getOutputStream())),
true);
out.println(str);
} catch (Exception e) {
e.printStackTrace();
}
}
class ClientThread implements Runnable {
@Override
public void run() {
try {
InetAddress serverAddr = InetAddress.getByName(SERVER_IP);
socket = new Socket(serverAddr, SERVERPORT);
} catch (IOException e1) {
e1.printStackTrace();
}
}
}
}
服务器.c
/*
C socket server example
*/
#include<stdio.h>
#include<string.h> //strlen
#include<sys/socket.h>
#include<arpa/inet.h> //inet_addr
#include<unistd.h> //write
int main(int argc , char *argv[])
{
int socket_desc , client_sock , c , read_size;
struct sockaddr_in server , client;
char client_message[2000];
//Create socket
socket_desc = socket(AF_INET , SOCK_STREAM , 0);
if (socket_desc == -1)
{
printf("Could not create socket");
}
puts("Socket created");
//Prepare the sockaddr_in structure
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons( 8888 );
//Bind
if( bind(socket_desc,(struct sockaddr *)&server , sizeof(server)) < 0)
{
//print the error message
perror("bind failed. Error");
return 1;
}
puts("bind done");
//Listen
listen(socket_desc , 3);
//Accept and incoming connection
puts("Waiting for incoming connections...");
c = sizeof(struct sockaddr_in);
//accept connection from an incoming client
client_sock = accept(socket_desc, (struct sockaddr *)&client, (socklen_t*)&c);
if (client_sock < 0)
{
perror("accept failed");
return 1;
}
puts("Connection accepted");
//Receive a message from client
while( (read_size = recv(client_sock , client_message , 2000 , 0)) > 0 )
{
//Send the message back to client
write(client_sock , client_message , strlen(client_message));
}
if(read_size == 0)
{
puts("Client disconnected");
fflush(stdout);
}
else if(read_size == -1)
{
perror("recv failed");
}
return 0;
}
当我尝试通过按下按钮发送消息时,这是 logcat:
2021-04-27 08:34:40.858 1185-1185/com.example.androdi_socket_example W/System.err: java.lang.NullPointerException: Attempt to invoke virtual method 'java.io.OutputStream java.net.Socket.getOutputStream()' on a null object reference
2021-04-27 08:34:40.859 1185-1185/com.example.androdi_socket_example W/System.err: at com.example.androdi_socket_example.MainActivity.onClick(MainActivity.java:36)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at java.lang.reflect.Method.invoke(Native Method)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at androidx.appcompat.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:409)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at android.view.View.performClick(View.java:6294)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1119)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at android.view.View$PerformClick.run(View.java:24770)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at android.os.Handler.handleCallback(Handler.java:790)
2021-04-27 08:34:40.860 1185-1185/com.example.androdi_socket_example W/System.err: at android.os.Handler.dispatchMessage(Handler.java:99)
2021-04-27 08:34:40.861 1185-1185/com.example.androdi_socket_example W/System.err: at android.os.Looper.loop(Looper.java:164)
2021-04-27 08:34:40.861 1185-1185/com.example.androdi_socket_example W/System.err: at android.app.ActivityThread.main(ActivityThread.java:6494)
2021-04-27 08:34:40.861 1185-1185/com.example.androdi_socket_example W/System.err: at java.lang.reflect.Method.invoke(Native Method)
2021-04-27 08:34:40.861 1185-1185/com.example.androdi_socket_example W/System.err: at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
2021-04-27 08:34:40.861 1185-1185/com.example.androdi_socket_example W/System.err: at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
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