Java下多种执行命令的姿势及问题
source link: https://y4er.com/post/java-exec-command/
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.
Java下多种执行命令的姿势及问题
2020-01-30Java中执行命令有很多姿势，但是有时候带有|,<,>等符号的命令没办法正常执行。为什么呢？
要想了解为什么，我们首先需要知道Java中有哪些方式可以执行命令。
Runtime
package exec;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
public class RuntimeExec {
public static void main(String[] args) throws Exception {
InputStream in = Runtime.getRuntime().exec("whoami").getInputStream();
byte[] bcache = new byte[1024];
int readSize = 0; //每次读取的字节长度
ByteArrayOutputStream infoStream = new ByteArrayOutputStream();
while ((readSize = in.read(bcache)) > 0) {
infoStream.write(bcache, 0, readSize);
}
System.out.println(infoStream.toString());
}
}
ProcessBuilder
package exec;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
public class ProcessExec {
public static void main(String[] args) {
try {
InputStream in = new ProcessBuilder("whoami").start().getInputStream();
byte[] bs = new byte[2048];
int readSize = 0; //每次读取的字节长度
ByteArrayOutputStream infoStream = new ByteArrayOutputStream();
while ((readSize = in.read(bs)) > 0) {
infoStream.write(bs, 0, readSize);
}
System.out.println(infoStream.toString());
} catch (Exception e) {
System.out.println(e.toString());
}
}
}
ProcessImpl
ProcessImpl是更为底层的实现，Runtime和ProcessBuilder执行命令实际上也是调用了ProcessImpl这个类，对于ProcessImpl类我们不能直接调用，但是可以通过反射来间接调用ProcessImpl来达到执行命令的目的。
package exec;
import java.io.ByteArrayOutputStream;
import java.lang.ProcessBuilder.Redirect;
import java.lang.reflect.Method;
import java.util.Map;
public class ProcessImplExec {
public static void main(String[] args) throws Exception {
String[] cmds = new String[]{"whoami"};
Class clazz = Class.forName("java.lang.ProcessImpl");
Method method = clazz.getDeclaredMethod("start", String[].class, Map.class, String.class, Redirect[].class, boolean.class);
method.setAccessible(true);
Process e = (Process) method.invoke(null, cmds, null, ".", null, true);
byte[] bs = new byte[2048];
int readSize = 0;
ByteArrayOutputStream infoStream = new ByteArrayOutputStream();
while ((readSize = e.getInputStream().read(bs)) > 0) {
infoStream.write(bs, 0, readSize);
}
System.out.println(infoStream.toString());
}
}
了解了Java中的几种执行命令的函数，我们来看下有什么问题。
Windows
在windows中，命令前缀要加cmd /c
package exec;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.Charset;
import java.util.Timer;
public class RuntimeExec {
public static void main(String[] args) {
Process process = null;
try {
String cmd ="echo 1 > 1.txt";
process = Runtime.getRuntime().exec(cmd);
BufferedReader br = new BufferedReader(new InputStreamReader(process.getInputStream(), Charset.forName("gbk")));
String line = null;
while ((line = br.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
加上cmd /c之后
打断点分析下，跟进exec()函数java.lang.Runtime#exec(java.lang.String)
public Process exec(String command) throws IOException {
return exec(command, null, null);
}
public Process exec(String command, String[] envp, File dir)
throws IOException {
if (command.length() == 0)
throw new IllegalArgumentException("Empty command");
StringTokenizer st = new StringTokenizer(command);
String[] cmdarray = new String[st.countTokens()];
for (int i = 0; st.hasMoreTokens(); i++)
cmdarray[i] = st.nextToken();
return exec(cmdarray, envp, dir);
}
先判断了command传入的命令是否为空，然后经过StringTokenizer类
继续往下看之后发现，经过StringTokenizer类之后返回了一个以空格分隔的数组
接着往下跟发现走到了
public Process exec(String[] cmdarray, String[] envp, File dir)
throws IOException {
return new ProcessBuilder(cmdarray)
.environment(envp)
.directory(dir)
.start();
}
也就是说Runtime的底层实际上还是ProcessBuilder。我们知道ProcessBuilder.start方法是命令执行，那么跟进这个start()。
发现String prog = cmdarray[0]拿到的就是我们可执行文件，然后判断security是否为null，如果不为null就会校验checkExec。接下来return了一个java.lang.ProcessImpl.start
也就是说Runtime和ProcessBuilder的底层实际上都是ProcessImpl。而不能执行echo命令的原因是因为java找不到这个东西，也就是没有环境变量。所以加上cmd /c就行了。
Linux
在谈Linux下的问题时，我们首先要知道一个点
如图所示，/bin/sh -c echo 111 > 3.txt虽然也创建了文件，但是并没有内容，也就是说我们一般通过/bin/sh -c "echo 111 > 3.txt"这种方式来写文件，转化为代码的话就是
String command="/bin/sh -c \"echo 111 > 3.txt\""
但是在上文我们知道了一点，StringTokenizer会根据空格将我们的命令划分为数组，那么我们的命令会被划分为{"/bin/sh","-c",""echo","111",">","3.txt""}，那么整个命令就变味了，达不到我们想要的效果。
怎么办呢？在ProcessBuilder中有几个构造方法，当传入字符串时会分割为数组
public ProcessBuilder(String... command) {
this.command = new ArrayList<>(command.length);
for (String arg : command)
this.command.add(arg);
}
public ProcessBuilder(List<String> command) {
if (command == null)
throw new NullPointerException();
this.command = command;
}
但是传入的是字符串数组时会直接this.command = command，避免了StringTokenizer的空格问题。
package exec;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.Charset;
public class RuntimeExec {
public static void main(String[] args) {
Process process = null;
try {
String[] cmd = {"/bin/sh", "-c", "echo 111 > 3.txt"};
process = Runtime.getRuntime().exec(cmd);
BufferedReader br = new BufferedReader(new InputStreamReader(process.getInputStream(), Charset.forName("gbk")));
String line = null;
while ((line = br.readLine()) != null) {
System.out.println(line);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
better？
有没有更好的办法？有的！Linux下可以用bash的base64编码，Windows下用powershell的base64编码。
文笔垃圾，措辞轻浮，内容浅显，操作生疏。不足之处欢迎大师傅们指点和纠正，感激不尽。
Recommend
About Joyk
Aggregate valuable and interesting links.
Joyk means Joy of geeK