java - 尝试通过管道将 C 中生成的数据传递给 Java 类。传递变量在java中显示为空白而不是有数据

Question

有 6 个文件/类:mainLaptop、Send、c_app、StreamTest、make file 和 ap.text。

我试图获取在 c 文件中处理的数据并将其传递给 java 文件中的变量。遵循本教程的“带字符串的管道”部分:http://www.jonathanbeard.io/tutorials/CtoJava

首先我打开终端并输入

1 make StreamTest
2 make c_app
3 java -cp . StreamTest
4 ./c_app

执行时，我看到“JAVA SIDE!!”接下来是终端中 c 进程的总数、计数和平均值(以及由于我的修改而导致的一些错误)

然后在 Eclipse 中我在 Eclipse 中运行 StreamTest

Eclipse 输出这个

JAVA SIDE: 
 [x] Sent ''Leonardo
 [x] Sent ''Raphael
 [x] Sent ''Donatello
 [x] Sent ''Michelangelo

但我需要它来输出这个

JAVA SIDE: 
 [x] Sent 'Total: 4953, Integers: 1000, Average: 4.9530'Leonardo
 [x] Sent 'Total: 4953, Integers: 1000, Average: 4.9530'Raphael
 [x] Sent 'Total: 4953, Integers: 1000, Average: 4.9530'Donatello
 [x] Sent 'Total: 4953, Integers: 1000, Average: 4.9530'Michelangelo

这是c代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <inttypes.h>

#define DEBUG 0
#define BUFFER 4096

//open ap.txt for text input
static const char* exFile = "ap.txt";
static char inputBuffer[BUFFER];

int main(int argc, const char** argv)
{
    FILE *fp = fopen(exFile,"r");
    /*check and see if the pointer is null in otherwords see if the memory 
      location refered to by fp is set...no memory location should be zero 
      if you want to reference it   
      Here are some good ways to do this other than the way I did it below:
      if(!fp) {do error}
      if(fp == NULL) {do error}
      and then there's the way I did it below
     */

    if(fp == 0){
        fprintf(stderr,"Null pointer exception, check file name.\n");
        exit(-1);
    }

    //check and see if an error occured during open
    const int err = ferror(fp);
    if(err != 0){
        /* void perror(const char* err) returns specific error message to string attached. */
        const char* errMessage = strcat("Something bad happened while opening file ",exFile);
        perror(errMessage);
    }
#if (DEBUG == 1)   
    else{
        fprintf(stderr,"Success opening file!!\n");
    }  
#endif


    setbuf(fp,inputBuffer); //set a buffer for input

    uint64_t *num = (uint64_t*) malloc(sizeof(uint64_t));
    uint64_t total = 0;
    uint64_t n = 0;

    //test for eof
    /*
       feof(*fp) - returns a boolean true if at end of file and false otherwise
     */

    while(!feof(fp)){
        //fscanf returns the number of items it converted using %llu, if it's not equal to 1 we don't want to continue
            if(fscanf(fp,"%"PRIu64"",num)!=1)
                break; //you could do a lot of stuff here as far as error handling but basically something bad has happened
            total+= *num; //add to total the value at memory location num
        n++;
#if (DEBUG == 1)   
        fprintf(stderr,"line number %"PRIu64"\n",n);
#endif 
    }

    free(num);

    const double average = (double) total / (double) n;
    //close the inputfile
    fclose(fp);

    //declare our outputfile, use a pipe in this case to a java process
    //we open a java process for this process to pipe to, also it is 
    //technically a bi-directional pipe so we can use any of the modifiers
    //like r/w/r+/etc
    static const char* outFile = "java -cp . StreamTest";

    FILE *fp_out = popen(outFile,"w");
    //setbuf(fp_out,outputBuffer);

    fprintf(fp_out,"Total: %"PRIu64", Integers: %"PRIu64", Average: 
            %.4f\n",total,n,average);



    /*
       int fflush(*fp) pushes any data in the buffer to be written
       the return value returns 0 if successful or !=0 if an error 
       occurs....remember return values in C often equal exceptions

     */   
    fflush(fp_out);

    /* int */
    fclose(fp_out);

    return 1;
}

这是生成文件

CC ?=gcc
JCC ?= javac
FLAGS ?= -Wall -O2
JFLAGS ?= -g -verbose

all: c_app StreamTest

c_app: c_app.c
    $(CC) $(FLAGS) -o c_app c_app.c

StreamTest: StreamTest.java
    $(JCC) $(JFLAGS) StreamTest.java $(LIBS)

clean:
    rm -f c_app StreamTest.class

ap.text 文件只是一堆数字

流测试

import java.io.BufferedInputStream; 
import java.io.IOException;
import java.io.InputStream;

public class StreamTest
{
private static final int buffer = 4096;

public static void main(String[] args) throws Exception 
{
    String pass=null;
    InputStream is = null;
    BufferedInputStream bis = null;
    try
    {
        bis = new BufferedInputStream(System.in,buffer);
        StringBuilder sb = new StringBuilder();
        //sb.append((char)bis.read());
        while(bis.available() > 0){
            sb.append((char)bis.read());
        }
        pass = sb.toString();
        System.out.println("JAVA SIDE: "+pass);
        bis.close();
    }
    catch(IOException ex)
    {

    }

    finally
    {


    }
    //pass = "hi";
    mainLaptop.main(pass);

}    
}

这是在 StreamTest 类中调用的 mainLaptop 类。

public class mainLaptop 
{

public static void main(String arg) throws Exception 
{   
    //Timing out? change the IP!
    String ip="192.168.137.127";
    String Pi1Q1="Leonardo";
    String Pi1Q2="Raphael";
    String Pi2Q3="Donatello";
    String Pi2Q4="Michelangelo";
    String pass=arg;

    Send.send(ip, Pi1Q1, pass);
    Send.send(ip, Pi1Q2, pass);
    Send.send(ip, Pi2Q3, pass);
    Send.send(ip, Pi2Q4, pass);

/*  Recv.recv(ip, Pi1Q1);
    Recv.recv(ip, Pi1Q2);
    Recv.recv(ip, Pi2Q3);
    Recv.recv(ip, Pi2Q4);*/
}
}

这是在我的 mainLaptop 类中调用的发送代码

import com.rabbitmq.client.Channel;     
import com.rabbitmq.client.Connection;
import com.rabbitmq.client.ConnectionFactory;

public class Send 
{

  public static void send(String ip, String Q, String pass) throws 
Exception 
  {

 ConnectionFactory factory = new ConnectionFactory();

//set connection info
factory.setHost(ip);
factory.setUsername("test");
factory.setPassword("test");

//create connection
Connection connection = factory.newConnection();

//create channel
Channel channel = connection.createChannel();

//publish message
   // int a = 1; 
//while (a!=0)
{
    channel.queueDeclare(Q, false, false, false, null);
    //for(int i=1; i<=2; i++)
    {
        //String message = pass;
        channel.basicPublish("", Q, null, pass.getBytes("UTF-8"));
        System.out.println(" [x] Sent '" + pass + "'" + Q);
    }

    //a--;      
}


//SHUT IT ALL DOWN!
channel.close();
connection.close();

  }
}

使用 @EJP 的一些建议编辑更新了流测试

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;

public class StreamTest{
private static final int buffer = 4096;
static String pass;
public static void main(String[] args) 
{
    InputStream is = null;
    BufferedInputStream bis = null;
    BufferedReader bir = null;
    try
    {
        bis = new BufferedInputStream(System.in,buffer);
        StringBuilder sb = new StringBuilder();



        while ((bir.readLine()) != null) 
        {
         // Do something here. Who knows
        }

        /*while(bis.available() > 0){
            sb.append((char)bis.read());
        }*/


        /*int b; 
        while ((b = bis.read()) != -1) 
        {
            // do something with 'b' 
            sb.append((char)b);

        }*/

        pass=sb.toString();

        System.out.println("JAVA SIDE: "+pass);
        bir.close();
        bis.close();
    }
    catch(IOException ex)
    {

    }
    finally{


    }


try {
mainLaptop.main(pass);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}
}

Answer 1

available() 不是流结束的测试。请参阅 Javadoc。摆脱它，并在 read() 返回 -1 时终止读取循环，或使用 BufferedReader.readLine() 并在返回 null 时终止。

并且不要忽略异常。

编辑为了让大家明白这一点，修改后的循环应为:

int b;
while ((b = bis.read()) != -1)
{
    sb.append((char)b);
}

或更可能

String line;
while ((line = bufferedReader.readLine()) != null)
{
    // Do something with 'line', other than merely appending it to a StringBuffer
}