Question

为什么没有输出？目标是使用以下命令通过tee管道telnet：

sh -c telnet rainmaker.wunderground.com 3000 | tee weather.txt

用于查看使用Java的telnet输出和日志服务器响应。（虽然有telnet库我试图使用系统telnet与exec，或类似的，而不是库。）

下面正确回显了命令，但没有输出显示：

thufir@mordor:~$ 
thufir@mordor:~$ java -jar NetBeansProjects/T/dist/T.jar 
Apr 05, 2016 4:36:56 AM net.bounceme.mordor.telnet.Main run
INFO: starting..
Apr 05, 2016 4:36:56 AM net.bounceme.mordor.telnet.Telnet <init>
INFO: connecting..
Apr 05, 2016 4:36:56 AM net.bounceme.mordor.telnet.PropertiesReader getConnection
INFO: starting..
Apr 05, 2016 4:36:56 AM net.bounceme.mordor.telnet.PropertiesReader getConnection
INFO: {weather.port=3000, weather.host=rainmaker.wunderground.com}
Apr 05, 2016 4:36:56 AM net.bounceme.mordor.telnet.Telnet getAddress
INFO: sh -c telnet rainmaker.wunderground.com 3000 | tee weather.txt
a
b
c
^CApr 05, 2016 4:37:01 AM net.bounceme.mordor.telnet.Telnet read
SEVERE: exiting.. 130
thufir@mordor:~$

此外，还没有创建weather.txt：

thufir@mordor:~$ 
thufir@mordor:~$ nl weather.txt
nl: weather.txt: No such file or directory
thufir@mordor:~$

代码：

package net.bounceme.mordor.telnet;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Properties;
import java.util.logging.Level;
import java.util.logging.Logger;

public class Telnet {

    private final static Logger LOG = Logger.getLogger(Telnet.class.getName());

    public Telnet() {
        LOG.info("connecting..");
    }

    private String getAddress() {
        Properties props = PropertiesReader.getConnection();
        String host = props.getProperty("weather.host");
        String port = props.getProperty("weather.port");
        String tee = " | tee weather.txt";
        String address = "sh -c telnet " + host + " " + port + tee;
        LOG.info(address);
        return address;
    }

    private void read(Process process) throws IOException, InterruptedException {
        BufferedReader input = new BufferedReader(new InputStreamReader(process.getInputStream()));
        String line = null;
        while ((line = input.readLine()) != null) {
            System.out.println(line);
        }
        int exitVal = process.waitFor();
        LOG.log(Level.SEVERE, "exiting.. {0}", exitVal);
    }

    private void useProcessBuilder() throws IOException, InterruptedException {
        LOG.info("using ProcessBuilder..");
        ProcessBuilder processBuilder = new ProcessBuilder("/bin/bash", "-c", getAddress());
        Process process = processBuilder.start();
        BufferedReader input = new BufferedReader(new InputStreamReader(process.getInputStream()));
        String line = null;
        while ((line = input.readLine()) != null) {
            System.out.println(line);
        }
        int exitVal = process.waitFor();
        LOG.log(Level.SEVERE, "done {0}", exitVal);
    }

    public void tryProcessBuilder() {
        try {
            useProcessBuilder();
        } catch (IOException | InterruptedException ex) {
            Logger.getLogger(Telnet.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    private void connect() throws IOException, InterruptedException {
        Runtime runtime = Runtime.getRuntime();
        Process process = runtime.exec(getAddress());
        read(process);
    }

    public void tryConnect() {
        try {
            connect();
        } catch (IOException | InterruptedException ex) {
            Logger.getLogger(Telnet.class.getName()).log(Level.SEVERE, null, ex);
        }
    }
}

虽然可以通过将管道留在发球台上来生成输出，但这并不能解决使用tee和telnet的问题。

另见：

陷阱的解决方案是简单地控制重定向分别处理外部进程的标准输出流 Runtime.exec（）方法。

http://www.javaworld.com/article/2071275/core-java/when-runtime-exec---won-t.html?page=2

Answer 1

唯一理解|的是shell。你需要执行一个shell来理解这个管道命令。

如何使用Java exec通过tee管道telnet

1 个答案: