BufferedWriter.write()与BufferedReader.readLine() (附带Java中的Runtime exec) / 憋错料

昨天在实现一个Java程序启动执行C++程序中，遇到了一些问题，先准备把它记录下来（利人利己）

准备实现的测试功能是这样的：在一个java程序中启动一个C++可执行程序，然后java程序和C++程序相互通信（java端发送消息给C++程序处理，C++处理完成后将返回一个结果消息给java程序。不断往返循环直至输入exit指令结束）。

首先，在一个java程序中启动一个C++可执行程序使用的是java的Runtime.getRuntime().exec()，Process类exec()官方说明 http://docs.oracle.com/javase/6/docs/api/java/lang/Process.html

【另外，还有一种java的JNI (Java Native Interface)框架可以实现java调用其它编程语言的方法】

*说明*：

使用exec()方式，C++程序的所有标准 io（即 stdin、stdout和
stderr）操作都将通过三个流(getOutputStream()、getInputStream()和
getErrorStream()) 重定向到父进程。

因此，使用上述重定向特性就可以通过标准输入输出实现Java与C++程序间的简单通信，在处理通信I/O时，使用了BufferedReader和BufferedWriter作为通信输入输出的缓冲，方便对消息处理。

关于readLine()，此处有篇博文点击打开链接 http://blog.csdn.net/swingline/article/details/5357581

*注意*：

1. 由于C++端是按行读取消息的，所以在Java端发送消息时要注意每个消息的结尾都必须加上换行符。这就是为何我在writeToCpp.write(wstr+"\n"); 中要+"\n"的原因。（就是因为这个换行符没加导致我调bug费了好长时间，之前一直找不出什么原因导致java端在console中输入消息发送后java程序就跑飞了。。后来发现在eclipse的console中输入字符串回车后该字符串末尾是不带换行符的。。。）

2. 下面的java代码中开辟了一个线程来处理从C++端传送来的消息打印。非常好用！

3. 【引用自点击打开链接】

误以为readLine()是读取到没有数据时就返回null(因为其它read方法当读到没有数据时返回-1)，而实际上readLine()是一个阻塞函数，当没有数据读取时，就一直会阻塞在那，而不是返回null；因为readLine()阻塞后，System.out.println(message)这句根本就不会执行到，所以在接收端就不会有东西输出。要想执行到System.out.println(message)，一个办法是发送完数据后就关掉流，这样readLine()结束阻塞状态，而能够得到正确的结果，但显然不能传一行就关一次数据流；另外一个办法是把System.out.println(message)放到while循环体内就可以。

另外有个问题没解决：

针对Java启动C++程序场景，如何配置使用eclipse和visual studio (2013)使得我能够从eclipse中debug Java程序跟踪到C++程序后能在Visual studio中继续能debug呢？

我查了下，好像可以通过Visual studio的attach to process功能能够实现联调（在VS中依次打开Debug -> Attach to process. 然后找到启动的java进程选中确定【我选的是javaw.exe】），但是我尝试了好久没有成功。（一开始提示找不到PDB文件，我就去vs的TOOLS -> Options -> Debugging -> Symbols勾选了“Microsoft Symbol Servers” ，部分PDB文件就可以加载了，但还有部分PDB文件加载不上。。。打的断点也是显示黄色圆圈带感叹号
【提示信息见下文】）

还请有经验的大侠能帮忙提供下eclipse与VS联调的解决方案，谢谢！！

下面就是实现了双边通信的java和C++源代码

Java端代码片段：

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.Scanner;

public class JavaCallCpp {

			static BufferedWriter writeToCpp;
			static BufferedReader readFromCpp;

	public static void main(String[] args) throws IOException {

		try {
			Process execute = Runtime.getRuntime().exec("D:/WorkSpace/vs/stringstream/Debug/stringstream");
			//int exitVal = execute.waitFor();
			writeToCpp = new BufferedWriter(new OutputStreamWriter(execute.getOutputStream()));
			readFromCpp = new BufferedReader(new InputStreamReader(execute.getInputStream()));

			MyThread myThread=new MyThread(readFromCpp);
			myThread.start();
			/*Write to C++*/
			writeToCpp.write("have entered the scentence\n");
			writeToCpp.write("aaaaa\n");
			writeToCpp.flush();

			//writeToCpp.write("quit\n");
			//writeToCpp.flush();
			/*Read from C++*/
			writeToCpp.write("abcd\n");
			writeToCpp.flush();
			Scanner writer = new Scanner(System.in);
//			while(true){
			String wstr = null;

			while(true){

					wstr=writer.next();
					if(wstr.equals("exit")){
						writer.close();
						break;
					}
					System.out.println(wstr);
					writeToCpp.write(wstr+"\n");
					writeToCpp.flush();
				}
			writeToCpp.flush();
				System.out.println("out of while.");
				/*while((readLine = readFromCpp.readLine()) != null){
					System.out.println(readLine);
				}*/
//			}
			//writerString.close();
			execute.destroyForcibly();//强制终止
			execute.getInputStream().close();
			readFromCpp.close();

		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}

class MyThread extends Thread{
	private BufferedReader bfr;
	public MyThread(BufferedReader bfr){
		this.bfr=bfr;
	}
	@Override
	public void run() {
		// TODO Auto-generated method stub
		super.run();
		String readLine = null;
		Boolean _b=true;
		try {
			while(_b){
				readLine=bfr.readLine();
				if(readLine==null)
				{
					_b=false;
				}else{
					System.out.println(readLine);
				}
			}
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
}

C++端程序片段：

void fun1(){
	string cmd;
	string line, word;
	cout << "enter a scentence, and exit with typing \"quit\""<<endl;
	while (getline(cin, line)&& line!="quit")
	{
		stringstream stream(line);
		cout << stream.str() << endl;
		while (stream >> word){ cout << word << endl; }
	}

	while (true){
		cout << "please input a command, and exit with typing \"exit\": "<<endl;
		getline(std::cin, cmd);
		if (0==strcmp(cmd.c_str(),"exit")){ //strcmp返回str1-str2的值
			cout << "cmd is exit, exit 0 \n";
			exit (0);
		}
		else if (strcmp(cmd.c_str(), "continue") !=0){
			cout << "cmd is not \"continue\" to break\n";
			continue;
		}
		else{
			cout << "cmd is continue, break while(true) \n";
			break;
		}
	}
	cout << "OK, pass over while(true) \n";
}

/*以下是针对debug问题的（可忽略）*/

eclipse与visual studio联调debug的提示信息：

'javaw.exe' (Win32): Loaded 'C:\Program Files\Java\jdk1.8.0_65\bin\javaw.exe'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\ntdll.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\kernel32.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\KernelBase.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\advapi32.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\msvcrt.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\sechost.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\rpcrt4.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\user32.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\gdi32.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\WinSxS\amd64_microsoft.windows.common-controls_6595b64144ccf1df_6.0.10586.0_none_8c15ae12515e1c22\comctl32.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\combase.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\bcryptprimitives.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\imm32.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Program Files\Java\jdk1.8.0_65\jre\bin\msvcr100.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Program Files\Java\jdk1.8.0_65\jre\bin\server\jvm.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\psapi.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\wsock32.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\ws2_32.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\version.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\winmm.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\winmmbase.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\cfgmgr32.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Program Files\Java\jdk1.8.0_65\jre\bin\verify.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Program Files\Java\jdk1.8.0_65\jre\bin\java.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Program Files\Java\jdk1.8.0_65\jre\bin\jdwp.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Program Files\Java\jdk1.8.0_65\jre\bin\npt.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Program Files\Java\jdk1.8.0_65\jre\bin\zip.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\shell32.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\windows.storage.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\shlwapi.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\kernel.appcore.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\SHCore.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\powrprof.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\profapi.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Program Files\Java\jdk1.8.0_65\jre\bin\dt_socket.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\NapiNSP.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\pnrpnsp.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\nlaapi.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\mswsock.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\dnsapi.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\nsi.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\winrnr.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\wshbth.dll'. Symbols loaded.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\FWPUCLNT.DLL'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\bcrypt.dll'. Cannot find or open the PDB file.
'javaw.exe' (Win32): Loaded 'C:\Windows\System32\rasadhlp.dll'. Cannot find or open the PDB file.

时间： 2024-10-11 11:27:50

BufferedWriter.write()与BufferedReader.readLine() (附带Java中的Runtime exec)

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