Runtime runtime = Runtime.getRuntime();

    NumberFormat format = NumberFormat.getInstance();

    StringBuilder sb = new StringBuilder();
    long maxMemory = runtime.maxMemory();
    long allocatedMemory = runtime.totalMemory();
    long freeMemory = runtime.freeMemory();

    sb.append("free memory: " + format.format(freeMemory / 1024) + "<br/>");
    sb.append("allocated memory: " + format.format(allocatedMemory / 1024) + "<br/>");
    sb.append("max memory: " + format.format(maxMemory / 1024) + "<br/>");
    sb.append("total free memory: " + format.format((freeMemory + (maxMemory - allocatedMemory)) / 1024) + "<br/>");