Java小工具

统计系统磁盘, 不需要其他依赖

public static void main(String[] args) throws IOException {
    DecimalFormat df = new DecimalFormat("#0.00");
    long diskSize = 0;
    long diskUsed = 0;
    File[] disks = File.listRoots();
    for (File file : disks) {
      // 获取盘符
      System.out.print(file.getCanonicalPath() + "   ");
      // 获取总容量
      long totalSpace = file.getTotalSpace();
      diskSize += totalSpace;
      // 获取剩余容量
      long usableSpace = file.getUsableSpace();
      // 获取已经使用的容量
      long freeSpace = totalSpace - usableSpace;
      diskUsed += freeSpace;
      // 获取使用率
      float useRate = (float)((freeSpace * 1.0 / totalSpace) * 100);
      System.out.print("总容量： " + totalSpace / 1024 / 1024 / 1024 + "GB    ");
      System.out.print("已经使用： " + freeSpace / 1024 / 1024 / 1024 + "GB    ");
      System.out.print("剩余容量： " + usableSpace / 1024 / 1024 / 1024 + "GB    ");
      System.out.println("使用率： " + Double.parseDouble(df.format(useRate)) + "%   ");
    }
    float useRate = (float)((diskUsed * 1.0 / diskSize) * 100);
    System.out.println("所有磁盘总容量："+diskSize / 1024 / 1024 / 1024 + "GB    ");
    System.out.println("所有磁盘已经使用："+diskUsed / 1024 / 1024 / 1024 + "GB    ");
    System.out.println("所有磁盘使用率："+ Double.parseDouble(df.format(useRate))+"%");
    System.out.println(new SystemDataController().findAll());
}

统计CPU和内存, 需要用到fastjson2

<dependency>
  <groupId>com.alibaba</groupId>
  <artifactId>fastjson</artifactId>
  <version>2.0.13</version>
</dependency>

public static void main(String[] args) {
    long GB = 1024 * 1024 * 1024;
    OperatingSystemMXBean operatingSystemMXBean = ManagementFactory.getOperatingSystemMXBean();
    String osJson = JSON.toJSONString(operatingSystemMXBean);
    System.out.println("osJson is " + osJson);
    JSONObject jsonObject = JSON.parseObject(osJson);
    double processCpuLoad = jsonObject.getDouble("processCpuLoad") * 100;
    double systemCpuLoad = jsonObject.getDouble("systemCpuLoad") * 100;
    Long totalPhysicalMemorySize = jsonObject.getLong("totalPhysicalMemorySize");
    Long freePhysicalMemorySize = jsonObject.getLong("freePhysicalMemorySize");
    double totalMemory = 1.0 * totalPhysicalMemorySize / GB;
    double freeMemory = 1.0 * freePhysicalMemorySize / GB;
    double memoryUseRatio = 1.0 * (totalPhysicalMemorySize - freePhysicalMemorySize) / totalPhysicalMemorySize * 100;
    
    StringBuilder result = new StringBuilder();
    result.append("系统CPU占用率: ")
        .append(twoDecimal(systemCpuLoad))
        .append("%，内存占用率：")
        .append(twoDecimal(memoryUseRatio))
        .append("%，系统总内存：")
        .append(twoDecimal(totalMemory))
        .append("GB，系统剩余内存：")
        .append(twoDecimal(freeMemory))
        .append("GB，该进程占用CPU：")
        .append(twoDecimal(processCpuLoad))
        .append("%");
    System.out.println(result.toString());
}
public static double twoDecimal(double doubleValue) {
    BigDecimal bigDecimal = new BigDecimal(doubleValue).setScale(2, RoundingMode.HALF_UP);
    return bigDecimal.doubleValue();
}

java递归树并分页

/**
* 分页
* @param idList 要查询的条件
* @param pageNum
* @param pageSize
* @return
*/
private PageInfo result(List<Object> idList, int pageNum, int pageSize){
    List<BaseMenuVO> result = selectTree("0", menuMapper.findByIds(idList));
    List<BaseMenuVO> baseMenuVOS = result
        .stream().skip((pageNum - 1) * pageSize).limit(pageSize).collect(Collectors.toList());
    PageInfo pageInfo = new PageInfo(result);
    pageInfo.setTotal(result.size());
    pageInfo.setList(baseMenuVOS);
    pageInfo.setPageNum(pageNum);
    pageInfo.setPageSize(pageSize);
    return pageInfo;
}

/**
* 生成树
* @param parentId 父级id
* @param treeEntityList 数据源
* @return
*/
private List<BaseMenuVO> selectTree(String parentId, List<BaseMenuVO> treeEntityList) {
    List<BaseMenuVO> collect = treeEntityList.stream()
        .filter(treeEntity -> treeEntity.getParentId().equals(parentId))
        .peek(treeEntity -> treeEntity.setChildren(selectTree(treeEntity.getId(), treeEntityList)))
        .collect(Collectors.toList());
    return collect;
}

求两个数组的差集、补集

List<String> deleteList =
    list1.stream().filter(e -> !list2.contains(e)).collect(Collectors.toList());
    
List<String> addList =
    list2.stream().filter(e -> !list1.contains(e)).collect(Collectors.toList());