Java简单实现本地文件读写操作

Java简单实现本地⽂件读写操作
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）
1public class Test {
2
3public static void main(String[] args) {
4boolean isFirst = true;
5try {
6 File file = new File("E:\\index_all.txt");
7 File outFile = new File("E:\\index.txt");
8if (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<>();
17while ((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);
26for (int i = 1; i < arr.length; i++) {
27 String[] line = arr[i].split(",");
28 String[] line2017 = arr[0].split(",");
29double 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
43double powAvg = 0, powSum = 0;
44if (line[4].startsWith("2017")) {
45if (isFirst) {
46 bufferedWriter2017.write("\r\n\r\n" + line2017[3] + "\t平均值" + "\t⽅差\r\n");
47 isFirst = false;
48 }
49double avg2017 = getAvg(line);
50int p = 0;
51for (int j = 9; j < line.length; j++) {
52if (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
78private static double getAvg(String[] line) {
79double sum = 0;
80int a = 0;
81for (int j = 9; j < line.length; j++) {
82if (line[j].length() > 0 && !line[j].startsWith("-999")) {
83 sum += Double.valueOf(line[j]);
84 a += 1;
85 }
86 }
87return 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
1public class Test {
2public static void main(String[] args) {
3boolean isFirst = true;
4 File file = new File("E:\\index_all.txt");
5if (file.isFile() && file.exists()) { //判断⽂件或⽬录是否存在
6try {
7 InputStream in = new FileInputStream(file);
8 File outFile = new File("E:\\index.txt");
9 OutputStream out = new FileOutputStream(outFile);
10try {
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<>();
18try {
19while ((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
29try {
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
33for (int i = 1; i < arr.length; i++) {
34 String[] line = arr[i].split(",");
35 String[] line2017 = arr[0].split(",");
36double 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
42double powAvg = 0, powSum = 0;
43if (line[4].startsWith("2017")) {
44if (isFirst) {
45 bufferedWriter2017.write("\r\n\r\n" + line2017[3] + "\t平均值" + "\t⽅差\r\n");
46 isFirst = false;
47 }
48double avg2017 = getAvg(line);
49int p = 0;
50for (int j = 9; j < line.length; j++) {
51if (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 {
66try {
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
87private static double getAvg(String[] line) {
88double sum = 0;
89int a = 0;
90for (int j = 9; j < line.length; j++) {
91if (line[j].length() > 0 && !line[j].startsWith("-999")) {
92 sum += Double.valueOf(line[j]);
93 a += 1;
94 }
95 }
96return 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)。