public static float getProcessCpuRate() {
float totalCpuTime1 = getTotalCpuTime();
float processCpuTime1 = getAppCpuTime();
try {
Thread.sleep(360);
}
catch (Exception e) {
}
float totalCpuTime2 = getTotalCpuTime();
float processCpuTime2 = getAppCpuTime();
float cpuRate = 100 * (processCpuTime2 - processCpuTime1) / (totalCpuTime2 - totalCpuTime1);
return cpuRate;
}
public static long getTotalCpuTime() {
// 获取系统总CPU使用时间 String[] cpuInfos = null;
try {
BufferedReader reader = new BufferedReader(new InputStreamReader( new FileInputStream("/proc/stat")), 1000);
String load = reader.readLine();
reader.close();
cpuInfos = load.split(" ");
}
catch (IOException ex) {
ex.printStackTrace();
}
long totalCpu = Long.parseLong(cpuInfos[2]) + Long.parseLong(cpuInfos[3]) + Long.parseLong(cpuInfos[4]) + Long.parseLong(cpuInfos[6]) + Long.parseLong(cpuInfos[5]) + Long.parseLong(cpuInfos[7]) + Long.parseLong(cpuInfos[8]);
return totalCpu;
}
public static long getAppCpuTime() {
// 获取应用占用的CPU时间 String[] cpuInfos = null;
try {
int pid = android.os.Process.myPid();
BufferedReader reader = new BufferedReader(new InputStreamReader( new FileInputStream("/proc/" + pid + "/stat")), 1000);
String load = reader.readLine();
reader.close();
cpuInfos = load.split(" ");
}
catch (IOException ex) {
ex.printStackTrace();
}
long appCpuTime = Long.parseLong(cpuInfos[13]) + Long.parseLong(cpuInfos[14]) + Long.parseLong(cpuInfos[15]) + Long.parseLong(cpuInfos[16]);
return appCpuTime;
}

计算某个时间段内AppCpuTime与TotalCpuTime的变化，然后按照比例换算成该应用的Cpu使用率。

Android系统本省也有一个类是用来显示Cpu使用率的：

android/system/frameworks/base/packages/SystemUI/src/com/android/systemui/LoadAverageService.java
阅读源码发现也是读取/proc目录下的文件来计算Cpu使用率

另外一种方式Runtime.getRuntime().exec("top -d 1 -n 1")，但是每次都获取到的cpu使用率为0，找不到原因

http://www.m2catalyst.com/tutorial-finding-cpu-usage-for-individual-android-apps/