Java簡單實現本地文件讀寫操做

問題：計算出大氣環流1到142項指數的所有年份的逐月平均值並輸出成文本，計算2017年每一個指數的方差並輸出成文本。（無效值 -999 不計算在內）

 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()) { //判斷文件或目錄是否存在
 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位小數
40                     bufferedWriter.flush(); //將緩衝區的內容輸出
41 
42                     // 計算2017年每一個指數的方差並輸出成文本
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); //計算平方和
54                                 p += 1;
55                             }
56                         }
57                         powAvg = powSum / p; //計算方差
58                         bufferedWriter2017.write(line[4] + "\t" + String.format("%.3f", avg) + "\t" + String.format("%.3f", powAvg) + "\r\n");
59                     }
60                 }
61                 bufferedWriter.flush(); //將緩衝區的內容輸出
62                 bufferedWriter2017.flush();
63                 bufferedWriter.close(); //①先關BufferedWriter 
64                 bufferedWriter2017.close();
65                 writer.close(); //②後關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("讀取文件內容出錯");
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 }

字節流和字符流：

• 字節流：通常是帶有Stream字樣的，如InputStream,FileInputStream等等，字節流處理的最小單位是字節。
• 字符流：通常是帶有Reader或Writer字樣的，如InputStreamReader等等，字符流處理的最小單位是字符。

02:14:33

時間緊，任務重，上面寫的太糙了...

修改以下

 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()) { //判斷文件或目錄是否存在
 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("異常：讀取文件出錯");
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); // 將List集合轉成String[]數組
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位小數
39                             bufferedWriter.flush(); //將緩衝區的內容輸出[沖刷出流(刷新此輸出流)，將全部緩衝的數據強制發送到目的地]
40 
41                             // 計算2017年每一個指數的方差並輸出成文本
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(); //將緩衝區的內容輸出[沖刷出流(刷新此輸出流)，將全部緩衝的數據強制發送到目的地]
61                         bufferedWriter2017.flush();
62                     } catch (IOException e) {
63                         System.out.println("異常：寫入文件出錯");
64                         e.printStackTrace();
65                     } finally {
66                         try {
67                             out.close(); // 直接調用最外層的close()就能夠，相似鏈條 你關閉最外面的 最外面的關閉裏面的 裏面的關閉更裏面的；
68                             in.close();
69                         } catch (IOException e) {
70                             System.out.println("異常：不支持編碼");
71                             e.printStackTrace();
72                         }
73                     }
74                 } catch (UnsupportedEncodingException e) {
75                     System.out.println("異常：不支持編碼");
76                     e.printStackTrace();
77                 }
78             } catch (FileNotFoundException e) {
79                 System.out.println("異常：文件未找到");
80                 e.printStackTrace();
81             }
82         } else {
83             System.out.println("文件或目錄不存在");
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 }

 讀取文件思路整理：(寫入文件思路相反，請自行百度)