Java 中的 Java.lang.Process 类
原文:https://www.geeksforgeeks.org/java-lang-process-class-java/
抽象的进程类一个进程——也就是一个正在执行的程序。流程提供的方法用于输入、输出、等待流程完成、检查流程退出状态和销毁流程。
- 它扩展了类对象。
- 它主要用作运行时类中 exec()创建的对象类型的超类。
- ProcessBuilder.start() 和runtime . getruntime . exec()方法创建一个本机进程，并返回一个进程子类的实例，该实例可用于控制该进程并获取有关该进程的信息。
- ProcessBuilder.start()是创建流程的最首选方式。
process builder . start()vs . runtime . getruntime . exec():process builder 允许我们将子进程的标准错误重定向到其标准输出中。现在我们不需要两个单独的线程一个从 stdout 读取，一个从 stderr 读取。
施工方
-
Process(): This is the only constructor.
方法:
- 虚空破坏():杀死子进程。
```java Syntax: public abstract void destroy(). Returns: NA. Exception: NA.
```
```java // Java code illustrating destroy() // method for windows operating system public class ProcessDemo public static void main(String[] args) { try {
// create a new process System.out.println("Creating Process");
ProcessBuilder builder = new ProcessBuilder("notepad.exe"); Process pro = builder.start();
// wait 10 seconds System.out.println("Waiting"); Thread.sleep(10000);
// kill the process pro.destroy(); System.out.println("Process destroyed");
} catch (Exception ex) { ex.printStackTrace(); } } } ```
输出:
```java Creating Process Waiting Process destroyed
```
```java // Java code illustrating destroy() // method for Mac Operating System import java.lang.; import java.io.; class ProcessDemo { public static void main(String arg[]) throws IOException, Exception { System.out.println("Creating process");
//creating process ProcessBuilder p = new ProcessBuilder(new String[] {"open", "/Applications/Facetime.app"}); Process pro = p.start();
//waiting for 10 second Thread.sleep(10000);
System.out.println("destroying process");
//destroying process pro.destroy(); } } ```
输出:
```java Creating process destroying process
```
- int exitValue(): This method returns the exit value for the subprocess.
```java Syntax: public abstract int exitValue(). Returns: This method returns the exit value of the subprocess represented by this Process object. By convention, the value 0 indicates normal termination. Exception: IllegalThreadStateException , if the subprocess represented by this Process object has not yet terminated.
```
```java // Java code illustrating exitValue() method public class ProcessDemo { public static void main(String[] args) { try { // create a new process System.out.println("Creating Process");
ProcessBuilder builder = new ProcessBuilder("notepad.exe"); Process pro = builder.start();
// kill the process pro.destroy();
// checking the exit value of subprocess System.out.println("exit value: " + pro.exitValue());
} catch (Exception ex) { ex.printStackTrace(); } } } ```
输出:
```java Creating Process 1
```
- abstract InputStream getErrorStream(): This method gets the input stream of the subprocess.
```java Syntax: public abstract InputStream getInputStream(). Returns: input stream that reads input from the process out output stream. Exception: NA.
```
```java // Java code illustrating // getInputStream() method import java.lang.; import java.io.; class ProcessDemo { public static void main(String arg[]) throws IOException, Exception { // creating the process Runtime r = Runtime.getRuntime();
// shell script for loop from 1 to 3 String[] nargs = {"sh", "-c", "for i in 1 2 3; do echo $i; done"}; Process p = r.exec(nargs);
BufferedReader is = new BufferedReader(new InputStreamReader(p.getInputStream())); String line;
// reading the output while ((line = is.readLine()) != null)
System.out.println(line); } } ```
输出:
```java 1 2 3
```
- abstract OutputStream getOutputStream(): This method gets the output stream of the subprocess. Output to the stream is piped into the standard input stream of the process represented by this Process object.
```java Syntax: public abstract OutputStream getOutputStream() Returns: the output stream connected to the normal input of the subprocess. Exception: NA.
```
```java // Java code illustrating // getOutputStream() method import java.io.BufferedOutputStream; import java.io.OutputStream;
public class ProcessDemo { public static void main(String[] args) { try { // create a new process System.out.println("Creating Process"); Process p = Runtime.getRuntime().exec("notepad.exe");
// get the output stream OutputStream out = p.getOutputStream();
// close the output stream System.out.println("Closing the output stream"); out.close(); } catch (Exception ex) { ex.printStackTrace(); } } } ```
输出:
```java Creating Process... Closing the output stream...
```
- abstract InputStream getErrorStream(): It returns an input stream that reads input from the process err output stream.
```java Syntax: public abstract InputStream getErrorStream(). Returns: the input stream connected to the error stream of the subprocess. Exception: NA.
```
```java // Java code illustrating // getErrorStream() method import java.io.InputStream;
public class ProcessDemo { public static void main(String[] args) { try { // create a new process System.out.println("Creating Process");
Process p = Runtime.getRuntime().exec("notepad.exe");
// get the error stream of the process and print it InputStream error = p.getErrorStream();
for (int i = 0; i < error.available(); i++) { System.out.println("" + error.read()); }
// wait for 10 seconds and then destroy the process Thread.sleep(10000); p.destroy();
}
catch (Exception ex) { ex.printStackTrace(); } } } ```
输出:
```java Creating Process
```
- int waitFor(): Returns the exit code returned by the process. This method does not return until the process on which it is called terminates.
```java Syntax: public int waitFor(). Returns: the exit value of the process. By convention, 0 indicates normal termination. Exception: throws InterruptedException.
```
```java // Java code illustrating // waitFor() method
public class ProcessDemo { public static void main(String[] args) { try { // create a new process System.out.println("Creating Process"); Process p = Runtime.getRuntime().exec("notepad.exe");
// cause this process to stop // until process p is terminated p.waitFor();
// when you manually close notepad.exe // program will continue here System.out.println("Waiting over"); } catch (Exception ex) { ex.printStackTrace(); } } } ```
输出:
```java Creating Process... Waiting over.
```
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