Hello Raspberry Pi: Java get CPU frequency by "cat /sys/.../scaling_cur

Monday, March 30, 2015

Java get CPU frequency by "cat /sys/.../scaling_cur_freq"

This example show Java program to get CPU frequency with Linux command "cat /sys/devices/system/cpu/cpu#/cpufreq/scaling_cur_freq", where # is the cpus' number.

Last post show a Python version to get CPU frequency, and the post in my another blog show a Android version. Here is a Java SE version.

JavaRead_scaling_cur_freq.java

package javaread_scaling_cur_freq;

import java.io.BufferedReader;
import java.io.File;
import java.io.FileFilter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.util.regex.Pattern;

public class JavaRead_scaling_cur_freq {

    public static void main(String[] args) {
        readCpuFreqNow();
    }

    static private void readCpuFreqNow() {
        File[] cpuFiles = getCPUs();
        System.out.println("number of cpu: " + cpuFiles.length);

        for (File cpuFile : cpuFiles) {
            String path_scaling_cur_freq 
                = cpuFile.getAbsolutePath() + "/cpufreq/scaling_cur_freq";
            System.out.println(path_scaling_cur_freq);
            System.out.println(cmdCat(path_scaling_cur_freq));
        }

    }
    
    //run Linux command 
    //$ cat f
    static private String cmdCat(String path){
        StringBuilder stringBuilder = new StringBuilder();
        
        Process process;
        try {
            process = Runtime.getRuntime().exec("cat " + path);
            process.waitFor();
            
            BufferedReader reader = 
                new BufferedReader(new InputStreamReader(process.getInputStream()));
            
            String line;   
            while ((line = reader.readLine())!= null) {
                stringBuilder.append(line).append("\n");
            }
            
        } catch (IOException | InterruptedException ex) {
            Logger.getLogger(JavaRead_scaling_cur_freq.class
                .getName()).log(Level.SEVERE, null, ex);
        }

        return stringBuilder.toString();
    }

    /*
     * Get file list of the pattern
     * /sys/devices/system/cpu/cpu[0..9]
     */
    static private File[] getCPUs() {

        class CpuFilter implements FileFilter {

            @Override
            public boolean accept(File pathname) {
                return Pattern.matches("cpu[0-9]+", pathname.getName());
            }
        }

        File dir = new File("/sys/devices/system/cpu/");
        File[] files = dir.listFiles(new CpuFilter());
        return files;
    }

}