Android基础篇

xiaoxiao2021-02-28  30

1.Ping是Windows、Unix和Linux系统下的一个命令。

ping也属于一个通信协议,是TCP/IP协议的一部分。

利用“ping”命令可以检查网络是否连通,可以很好地帮助我们分析和判定网络故障。

Ping发送一个ICMP (Internet Control Messages Protocol)即因特网信报控制协议,回声请求消息给目的地并报告是否收到所希望的 ICMP  echo (ICMP回声应答),用来检查网络是否通畅或者网络连接速度的命令。广义来说即发送一个数据包,根据返回的数据包得到丢包率及平均时间得出网络的连接状态。 ping命令可以用在android中检测网络ip或者socket的连接,命令格式:ping ip地址(最简) ping具有一些参数,可以具体定义包的个数、包的最大存活时间等

2.具体参数:

参数详解-aAudible ping.-A自适应ping,根据ping包往返时间确定ping的速度;-b允许ping一个广播地址;-B不允许ping改变包头的源地址;-c countping指定次数后停止ping; -d 使用Socket的SO_DEBUG功能;-F flow_label为ping回显请求分配一个20位的“flow label”,如果未设置,内核会为ping随机分配;-f极限检测,快速连续ping一台主机,ping的速度达到100次每秒;-i interval设定间隔几秒发送一个ping包,默认一秒ping一次;-I interface指定网卡接口、或指定的本机地址送出数据包;-l preload设置在送出要求信息之前,先行发出的数据包;-L抑制组播报文回送,只适用于ping的目标为一个组播地址-n 不要将ip地址转换成主机名;-p pattern指定填充ping数据包的十六进制内容,在诊断与数据有关的网络错误时这个选项就非常有用,如:“-p ff”;-q不显示任何传送封包的信息,只显示最后的结果-Q tos设置Qos(Quality of Service),它是ICMP数据报相关位;可以是十进制或十六进制数,详见rfc1349和rfc2474文档;-R记录ping的路由过程(IPv4 only);注意:由于IP头的限制,最多只能记录9个路由,其他会被忽略;-r忽略正常的路由表,直接将数据包送到远端主机上,通常是查看本机的网络接口是否有问题;如果主机不直接连接的网络上,则返回一个错误。-S sndbufSet socket sndbuf. If not specified, it is selected to buffer not more than one packet.-s packetsize指定每次ping发送的数据字节数,默认为“56字节”+“28字节”的ICMP头,一共是84字节;包头+内容不能大于65535,所以最大值为65507(linux:65507, windows:65500);-t ttl设置TTL(Time To Live)为指定的值。该字段指定IP包被路由器丢弃之前允许通过的最大网段数;-T timestamp_option设置IP timestamp选项,可以是下面的任何一个:  'tsonly' (only timestamps)  'tsandaddr' (timestamps and addresses)  'tsprespec host1 [host2 [host3]]' (timestamp prespecified hops). -M hint 设置MTU(最大传输单元)分片策略。可设置为:  'do':禁止分片,即使包被丢弃;  'want':当包过大时分片;  'dont':不设置分片标志(DF flag);-m mark设置mark;-v使ping处于verbose方式,它要ping命令除了打印ECHO-RESPONSE数据包之外,还打印其它所有返回的ICMP数据包;-U Print full user-to-user latency (the old behaviour).Normally ping prints network round trip time, which can be different f.e. due to DNS failures.-W timeout以毫秒为单位设置ping的超时时间;-w deadlinedeadline; 当然,这只是个小的例子,结合上面给的参数,你爱ping什么ping什么

3.Runtime.exec():

ping这个命令其实也没什么可说的,主要想再说说Runtime.exec()方法,这个方法不单纯只是Ping,其实他能完成几乎所有的Linux命令结果 还有Process类,顾名思义Process进程(Process)是计算机中的程序关于某数据集合上的一次运行活动,是系统进行资源分配和调度的基本单位,是操作系统结构的基础。 这个类,有获取读写流的方法,就说明我们刚才的exec会以流的方式返回结果。

3.1.Runtime

好,最后重点说一下Runtime,他在java.lang包下面,

/** * Executes the specified command and its arguments in a separate native * process. The new process inherits the environment of the caller. Calling * this method is equivalent to calling {@code exec(progArray, null, null)}. * * @param progArray * the array containing the program to execute as well as any * arguments to the program. * @return the new {@code Process} object that represents the native * process. * @throws IOException * if the requested program can not be executed. */ public Process exec(String[] progArray) throws java.io.IOException { return exec(progArray, null, null); } /** * Executes the specified command and its arguments in a separate native * process. The new process uses the environment provided in {@code envp}. * Calling this method is equivalent to calling * {@code exec(progArray, envp, null)}. * * @param progArray * the array containing the program to execute as well as any * arguments to the program. * @param envp * the array containing the environment to start the new process * in. * @return the new {@code Process} object that represents the native * process. * @throws IOException * if the requested program can not be executed. */ public Process exec(String[] progArray, String[] envp) throws java.io.IOException { return exec(progArray, envp, null); } /** * Executes the specified command and its arguments in a separate native * process. The new process uses the environment provided in {@code envp} * and the working directory specified by {@code directory}. * * @param progArray * the array containing the program to execute as well as any * arguments to the program. * @param envp * the array containing the environment to start the new process * in. * @param directory * the directory in which to execute the program. If {@code null}, * execute if in the same directory as the parent process. * @return the new {@code Process} object that represents the native * process. * @throws IOException * if the requested program can not be executed. */ public Process exec(String[] progArray, String[] envp, File directory) throws IOException { // ProcessManager is responsible for all argument checking. return ProcessManager.getInstance().exec(progArray, envp, directory, false); } /** * Executes the specified program in a separate native process. The new * process inherits the environment of the caller. Calling this method is * equivalent to calling {@code exec(prog, null, null)}. * * @param prog * the name of the program to execute. * @return the new {@code Process} object that represents the native * process. * @throws IOException * if the requested program can not be executed. */ public Process exec(String prog) throws java.io.IOException { return exec(prog, null, null); } /** * Executes the specified program in a separate native process. The new * process uses the environment provided in {@code envp}. Calling this * method is equivalent to calling {@code exec(prog, envp, null)}. * * @param prog * the name of the program to execute. * @param envp * the array containing the environment to start the new process * in. * @return the new {@code Process} object that represents the native * process. * @throws IOException * if the requested program can not be executed. */ public Process exec(String prog, String[] envp) throws java.io.IOException { return exec(prog, envp, null); } /** * Executes the specified program in a separate native process. The new * process uses the environment provided in {@code envp} and the working * directory specified by {@code directory}. * * @param prog * the name of the program to execute. * @param envp * the array containing the environment to start the new process * in. * @param directory * the directory in which to execute the program. If {@code null}, * execute if in the same directory as the parent process. * @return the new {@code Process} object that represents the native * process. * @throws IOException * if the requested program can not be executed. */ public Process exec(String prog, String[] envp, File directory) throws java.io.IOException { // Sanity checks if (prog == null) { throw new NullPointerException("prog == null"); } else if (prog.isEmpty()) { throw new IllegalArgumentException("prog is empty"); } // Break down into tokens, as described in Java docs StringTokenizer tokenizer = new StringTokenizer(prog); int length = tokenizer.countTokens(); String[] progArray = new String[length]; for (int i = 0; i < length; i++) { progArray[i] = tokenizer.nextToken(); } // Delegate return exec(progArray, envp, directory); }

prog时需要执行的程序,怎么理解,其实很简单,就是系统的command命令,到这大家应该都清楚了,Android是Linux系统,这里的指令也就是Linux的命令了,例如ps(查看进程),ls,pwd(查看现在路径,文件等等)等等,大家都可以去试试。

*注意点:

    1、exec的String prog只能执行一条指令,如果需要执行多条指令需要放入sh脚本文件中执行或者调用多次exec函数。

    2、exec的String command不支持通配符(*)。

    3、有些指令需要指定File dir(工作目录)。

    4、默认的工作目录是根目录/。(通过执行指令pwd可查到)

    5、导出logcat日志到SD卡ziyouku目录,参数:("logcat -df logcat.log",new File("/mnt/sdcard/ziyouku/"))

    6、logcat读取权限:<uses-permission android:name="android.permission.READ_LOGS" />

好,今天就说这么多,最近在做Spingboot开发后台并发系统,所以写博客也是对之前项目的很多技术点的总结完善。

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