如何從Java運行命令行命令

使用Runtime.exec()可執行外部命令，但需用字符串數組避免空格問題；2. 推薦使用ProcessBuilder，因其更靈活，可設置環境變量、工作目錄且語法清晰；3. 應同時讀取stdout和stderr並處理輸入輸出流；4. 避免命令注入，妥善處理異常和流關閉；5. 注意命令的平台依賴性，新代碼應優先使用ProcessBuilder以確保安全性和可維護性。

You can run a command line command from Java using the Runtime.exec() method or the ProcessBuilder class. Both approaches allow you to execute external system commands and interact with their input/output streams. Here's how to use each method effectively.

Using Runtime.getRuntime().exec()

This is the traditional way to run external commands.

 import java.io.BufferedReader;
import java.io.InputStreamReader;

public class RunCommand {
    public static void main(String[] args) {
        try {
            // Example: Run 'ls -l' on Linux/Mac or 'dir' on Windows
            Process process = Runtime.getRuntime().exec("ls -l");

            // Read the output
            BufferedReader reader = new BufferedReader(
                new InputStreamReader(process.getInputStream())
            );

            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }

            // Wait for the command to finish
            int exitCode = process.waitFor();
            System.out.println("Command exited with code: " exitCode);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Notes:

• Pass the command as a string or a string array (recommended for arguments with spaces).
• Use a string array to avoid issues with spaces and special characters:

   Runtime.getRuntime().exec(new String[]{"ls", "-l", "/some/directory"});

Using ProcessBuilder (Recommended)

ProcessBuilder is more flexible and easier to manage, especially for complex commands.

 import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.Arrays;

public class RunCommandWithBuilder {
    public static void main(String[] args) {
        try {
            // Build the command
            ProcessBuilder pb = new ProcessBuilder(Arrays.asList("ls", "-l"));

            // Optional: Set working directory
            // pb.directory(new File("/path/to/dir"));

            // Start the process
            Process process = pb.start();

            // Read output
            BufferedReader reader = new BufferedReader(
                new InputStreamReader(process.getInputStream())
            );

            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }

            // Wait and get exit code
            int exitCode = process.waitFor();
            System.out.println("Exit code: " exitCode);

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Advantages of ProcessBuilder :

• Better handling of command arguments.
• Easy to set environment variables: pb.environment().put("VAR", "value") .
• Can set working directory with pb.directory(new File("/path")) .
• Cleaner syntax for complex commands.

Handling Errors and Input

Commands may produce error output, so it's good practice to read both stdout and stderr:

 BufferedReader errorReader = new BufferedReader(
    new InputStreamReader(process.getErrorStream())
);
String errorLine;
while ((errorLine = errorReader.readLine()) != null) {
    System.err.println(errorLine);
}

If your command requires input (eg, interactive scripts), write to the process's output stream:

 try (BufferedWriter writer = new BufferedWriter(
     new OutputStreamWriter(process.getOutputStream()))) {
    writer.write("yes");
    writer.newLine();
    writer.flush();
}

Security and Best Practices

• Avoid injecting user input directly into commands (risk of command injection).
• Prefer ProcessBuilder for better control.
• Always handle exceptions and close streams properly.
• Be aware that commands are OS-dependent (eg, dir vs ls ).

Basically, use ProcessBuilder for new code — it's clearer, safer, and more maintainable. Just remember to handle output, errors, and platform differences.

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