Java简单实现本地文件读写操作

àì夳堔傛蜴生んèń 2021-12-03 16:32 419阅读 0赞

问题：计算出大气环流1到142项指数的全部年份的逐月平均值并输出成文本，计算2017年每个指数的方差并输出成文本。（无效值 -999 不计算在内）

1 public class Test {
     2 
     3     public static void main(String[] args) {
     4         boolean isFirst = true;
     5         try {
     6             File file = new File("E:\\index_all.txt");
     7             File outFile = new File("E:\\index.txt");
     8             if (file.isFile() && file.exists()) { //判断文件或目录是否存在
     9                 InputStreamReader reader = new InputStreamReader(new FileInputStream(file), "utf-8");
    10                 BufferedReader bufferedReader = new BufferedReader(reader);
    11                 OutputStreamWriter writer = new OutputStreamWriter(new FileOutputStream(outFile), "gbk");
    12                 BufferedWriter bufferedWriter = new BufferedWriter(writer);
    13                 OutputStreamWriter writer2017 = new OutputStreamWriter(new FileOutputStream(outFile), "gbk");
    14                 BufferedWriter bufferedWriter2017 = new BufferedWriter(writer);
    15                 String lineTxt = null;
    16                 List<String> list = new ArrayList<>();
    17                 while ((lineTxt = bufferedReader.readLine()) != null) {
    18                     System.out.println(lineTxt);
    19                     list.add(lineTxt.replace(" ", ","));
    20 //                    bufferedWriter.write(lineTxt+"\r\n");
    21                 }
    22                 bufferedWriter.write(list.get(0).replace(",", " ") + "\tavg\r\n");
    23 
    24                 String[] arr = new String[list.size()];
    25                 arr = list.toArray(arr);
    26                 for (int i = 1; i < arr.length; i++) {
    27                     String[] line = arr[i].split(",");
    28                     String[] line2017 = arr[0].split(",");
    29                     double avg = 0, sum = 0;
    30                     /*int a = 0;
    31                     for (int j = 9; j < line.length; j++) {
    32                         if (line[j].length() > 0 && !line[j].startsWith("-999")) {
    33                             sum += Double.valueOf(line[j]);
    34                             a += 1;
    35                         }
    36                     }
    37                     avg = sum / a;*/
    38                     avg = getAvg(line);
    39                     bufferedWriter.write(list.get(i).replace(",", " ") + "\t" + String.format("%.3f", avg) + "\r\n"); //保留3位小数
    40                     bufferedWriter.flush(); //将缓冲区的内容输出
    41 
    42                     // 计算2017年每个指数的方差并输出成文本
    43                     double powAvg = 0, powSum = 0;
    44                     if (line[4].startsWith("2017")) {
    45                         if (isFirst) {
    46                             bufferedWriter2017.write("\r\n\r\n" + line2017[3] + "\t平均值" + "\t方差\r\n");
    47                             isFirst = false;
    48                         }
    49                         double avg2017 = getAvg(line);
    50                         int p = 0;
    51                         for (int j = 9; j < line.length; j++) {
    52                             if (line[j].length() > 0 && !line[j].startsWith("-999")) {
    53                                 powSum += Math.pow((Double.valueOf(line[j]) - avg2017), 2); //计算平方和
    54                                 p += 1;
    55                             }
    56                         }
    57                         powAvg = powSum / p; //计算方差
    58                         bufferedWriter2017.write(line[4] + "\t" + String.format("%.3f", avg) + "\t" + String.format("%.3f", powAvg) + "\r\n");
    59                     }
    60                 }
    61                 bufferedWriter.flush(); //将缓冲区的内容输出
    62                 bufferedWriter2017.flush();
    63                 bufferedWriter.close(); //①先关BufferedWriter 
    64                 bufferedWriter2017.close();
    65                 writer.close(); //②后关OutputStreamWriter 
    66                 writer2017.close();
    67                 bufferedReader.close();
    68                 reader.close();
    69             } else {
    70                 System.out.println("找不到指定的文件");
    71             }
    72         } catch (Exception e) {
    73             System.out.println("读取文件内容出错");
    74             e.printStackTrace();
    75         }
    76     }
    77 
    78     private static double getAvg(String[] line) {
    79         double sum = 0;
    80         int a = 0;
    81         for (int j = 9; j < line.length; j++) {
    82             if (line[j].length() > 0 && !line[j].startsWith("-999")) {
    83                 sum += Double.valueOf(line[j]);
    84                 a += 1;
    85             }
    86         }
    87         return sum / a;
    88     }
    89 }

字节流和字符流：

*  字节流：一般是带有Stream字样的，如InputStream,FileInputStream等等，字节流处理的最小单位是字节。
 *  字符流：一般是带有Reader或Writer字样的，如InputStreamReader等等，字符流处理的最小单位是字符。

02:14:33

时间紧，任务重，上面写的太糙了...

修改如下

1 public class Test {
     2     public static void main(String[] args) {
     3         boolean isFirst = true;
     4         File file = new File("E:\\index_all.txt");
     5         if (file.isFile() && file.exists()) { //判断文件或目录是否存在
     6             try {
     7                 InputStream in = new FileInputStream(file);
     8                 File outFile = new File("E:\\index.txt");
     9                 OutputStream out = new FileOutputStream(outFile);
    10                 try {
    11                     Reader reader = new InputStreamReader(in, "utf-8");
    12                     BufferedReader bufferedReader = new BufferedReader(reader);
    13                     Writer writer = new OutputStreamWriter(out, "gbk");
    14                     BufferedWriter bufferedWriter = new BufferedWriter(writer);
    15                     BufferedWriter bufferedWriter2017 = new BufferedWriter(writer);
    16                     String lineTxt = null;
    17                     List<String> list = new ArrayList<>();
    18                     try {
    19                         while ((lineTxt = bufferedReader.readLine()) != null) {
    20                             System.out.println(lineTxt);
    21                             list.add(lineTxt.replace(" ", ","));
    22 //                            bufferedWriter.write(lineTxt + "\r\n");
    23                         }
    24                     } catch (IOException e) {
    25                         System.out.println("异常：读取文件出错");
    26                         e.printStackTrace();
    27                     }
    28 
    29                     try {
    30                         bufferedWriter.write(list.get(0).replace(",", " ") + "\tavg\r\n");
    31                         String[] arr = new String[list.size()];
    32                         arr = list.toArray(arr); // 将List集合转成String[]数组
    33                         for (int i = 1; i < arr.length; i++) {
    34                             String[] line = arr[i].split(",");
    35                             String[] line2017 = arr[0].split(",");
    36                             double avg = 0, sum = 0;
    37                             avg = getAvg(line);
    38                             bufferedWriter.write(list.get(i).replace(",", " ") + "\t" + String.format("%.3f", avg) + "\r\n"); // 保留3位小数
    39                             bufferedWriter.flush(); //将缓冲区的内容输出[冲刷出流(刷新此输出流)，将所有缓冲的数据强制发送到目的地]
    40 
    41                             // 计算2017年每个指数的方差并输出成文本
    42                             double powAvg = 0, powSum = 0;
    43                             if (line[4].startsWith("2017")) {
    44                                 if (isFirst) {
    45                                     bufferedWriter2017.write("\r\n\r\n" + line2017[3] + "\t平均值" + "\t方差\r\n");
    46                                     isFirst = false;
    47                                 }
    48                                 double avg2017 = getAvg(line);
    49                                 int p = 0;
    50                                 for (int j = 9; j < line.length; j++) {
    51                                     if (line[j].length() > 0 && !line[j].startsWith("-999")) {
    52                                         powSum += Math.pow((Double.valueOf(line[j]) - avg2017), 2);
    53                                         p += 1;
    54                                     }
    55                                 }
    56                                 powAvg = powSum / p;
    57                                 bufferedWriter2017.write(line[4] + "\t" + String.format("%.3f", avg) + "\t" + String.format("%.3f", powAvg) + "\r\n");
    58                             }
    59                         }
    60                         bufferedWriter.flush(); //将缓冲区的内容输出[冲刷出流(刷新此输出流)，将所有缓冲的数据强制发送到目的地]
    61                         bufferedWriter2017.flush();
    62                     } catch (IOException e) {
    63                         System.out.println("异常：写入文件出错");
    64                         e.printStackTrace();
    65                     } finally {
    66                         try {
    67                             out.close(); // 直接调用最外层的close()就可以，类似链条 你关闭最外面的 最外面的关闭里面的 里面的关闭更里面的；
    68                             in.close();
    69                         } catch (IOException e) {
    70                             System.out.println("异常：不支持编码");
    71                             e.printStackTrace();
    72                         }
    73                     }
    74                 } catch (UnsupportedEncodingException e) {
    75                     System.out.println("异常：不支持编码");
    76                     e.printStackTrace();
    77                 }
    78             } catch (FileNotFoundException e) {
    79                 System.out.println("异常：文件未找到");
    80                 e.printStackTrace();
    81             }
    82         } else {
    83             System.out.println("文件或目录不存在");
    84         }
    85     }
    86 
    87     private static double getAvg(String[] line) {
    88         double sum = 0;
    89         int a = 0;
    90         for (int j = 9; j < line.length; j++) {
    91             if (line[j].length() > 0 && !line[j].startsWith("-999")) {
    92                 sum += Double.valueOf(line[j]);
    93                 a += 1;
    94             }
    95         }
    96         return sum / a;
    97     }
    98 }

读取文件思路整理：(写入文件思路相反，请自行百度)

![824778-20190714003953769-1136032674.png][]

转载于:https://www.cnblogs.com/wq-code/p/11178572.html

[824778-20190714003953769-1136032674.png]: /images/20211203/0e668db622004c8d94f99da5eb6a090a.png