java 运行 ps -ef | grep tomcat 得不到返回值

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public class Test {

public static void main(String[] args) throws IOException {

// String cmd = "kill -9 812";

String cmd = "ps -ef | grep tomcat";

Process ps = Runtime.getRuntime().exec(cmd);

load(ps.getInputStream());

}

public static void load(InputStream is) throws IOException{

int ptr = 0;

is = new BufferedInputStream(is);

StringBuffer buffer = new StringBuffer();

while((ptr = is.read()) != -1){

buffer.append((char)ptr);

}

// System.out.println(buffer.toString());

String data = buffer.toString();

// String[] str = data.split("\n");

// System.out.println("length : "+str.length+" data : "+str[0]+" -- "+str[1].split(" ")[0]);

System.out.println(data);

}

}