Java读写文件方法总结

1 package 天才白痴梦;
2
3 import java.io.BufferedReader;
4 import java.io.File;
5 import java.io.FileInputStream;
6 import java.io.FileReader;
7 import java.io.IOException;
8 import java.io.InputStream;
9 import java.io.InputStreamReader;
10 import java.io.RandomAccessFile;
11 import java.io.Reader;
12
13 public class JavaIO {
14
15     /**
16      * 采用的是操作系统底层默认的编码方式，GBK等，非UTF8
17      * */
18
19     /**
20      * 以字节为单位读取文件内容，常用于读取二进制文件，比如图片、影像、声音等文件
21      * */
22     public static void readFileByBytes(String filename) {
23         File file=new File(filename);
24         FileInputStream in=null;
25         try {
26             System.out.println("以字节为单位读取文件,一次读一个字节: ");
27             in=new FileInputStream(file);
28             int temp=0;
29             while ((temp=in.read()) != -1) {
30                 System.out.println(temp);
31             }
32             in.close();
33         } catch (IOException e) {
34             e.printStackTrace();
35             return ;
36         }
37         try {
38             System.out.println("以字节为单位读取文件，一次读多个字节： ");
39             byte[] temp=new byte[100];
40             int byteread=0;
41             in=new FileInputStream(file);
42             JavaIO.showAvailableBytes(in);
43             while ((byteread=in.read(temp)) != -1) {
44                 System.out.write(temp,0,byteread);
45             }
46         } catch (Exception e1) {
47             e1.printStackTrace();
48         } finally {
49             if (in != null) {
50                 try {
51                     in.close();
52                 } catch (IOException e1) {
53
54                 }
55             }
56         }
57     }
58     /**
59      * 以字符为单位读取文件，常用于读文本，数字等类型的文件
60      * */
61     public static void readFileByChar(String filename) {
62         File file=new File(filename);
63         Reader reader=null;
64         try {
65             System.out.println("以字符为单位读取文件内容，一次一个字节：");
66             //InputStreamReader类:是字节向字符转换的桥梁
67             reader=new InputStreamReader(new FileInputStream(file));
68             int temp;
69             while ((temp=reader.read()) != -1) {
70                 if (((char)temp) != '\r') {
71                     System.out.println((char)temp);
72                 }
73             }
74             reader.close();
75         } catch (Exception e) {
76             e.printStackTrace();
77         }
78         try {
79             System.out.println("以字符为单位读取文件内容，一次读多个字节： ");
80             char[] temp=new char[30];
81             int charread=0;
82             reader=new InputStreamReader(new FileInputStream(filename));
83             while ((charread=reader.read(temp)) != -1) {
84                 if ((charread == temp.length) && (temp[temp.length-1]!='\r')) {
85                     System.out.println(temp);
86                 } else {
87                     for (int i=0; i<charread; i++) {
88                         if (temp[i] == '\r') {
89                             break;
90                         } else {
91                             System.out.println(temp[i]);
92                         }
93                     }
94                 }
95             }
96         } catch (Exception e) {
97             e.printStackTrace();
98         } finally {
99             if (reader != null) {
100                 try {
101                     reader.close();
102                 } catch (IOException e) {
103
104                 }
105             }
106         }
107     }
108     /**
109      * 以行为单位读取文件，常用于读面向行的格式化文件
110      * */
111     public static void readFileByLine(String filename) {
112         File file=new File(filename);
113         BufferedReader reader=null;
114         try {
115             System.out.println("以行为单位读取文件内容，一次读一整行： ");
116             reader=new BufferedReader(new FileReader(file));
117             String temp=null;
118             int line=1;
119             while ((temp=reader.readLine()) != null) {
120                 System.out.println("line " + line + ": " + temp);
121                 line++;
122             }
123             reader.close();
124         } catch (IOException e) {
125             e.printStackTrace();
126         } finally {
127             if (reader != null) {
128                 try {
129                     reader.close();
130                 } catch (IOException e) {
131
132                 }
133             }
134         }
135     }
136     /**
137      * 随机读取文件内容
138      * */
139     public static void readFileByRandomAccess(String filename) {
140         RandomAccessFile randomfile=null;
141         try {
142             System.out.println("随机读取一段文件内容");
143             randomfile=new RandomAccessFile(filename,"r");
144             long fileLength=randomfile.length();
145             int beginIndex=(fileLength > 4 ? 4 : 0);
146             randomfile.seek(beginIndex);
147             byte[] bytes=new byte[10];
148             int byteread=0;
149             while ((byteread=randomfile.read(bytes)) != -1) {
150                 System.out.write(bytes,0,byteread);
151             }
152         } catch (IOException e) {
153             e.printStackTrace();
154         } finally {
155             if (randomfile != null) {
156                 try {
157                     randomfile.close();
158                 } catch (IOException e) {
159
160                 }
161             }
162         }
163     }
164     private static void showAvailableBytes(InputStream in) {
165         try {
166             System.out.println("当前字节输入流中的字节数为：" + in.available());
167         } catch (IOException e) {
168             e.printStackTrace();
169         }
170     }
171     public static void main(String[] args) {
172         String filename="E:\\BaiYiShaoNian.txt";
173         JavaIO.readFileByBytes(filename);
174         JavaIO.readFileByChar(filename);
175         JavaIO.readFileByLine(filename);
176         JavaIO.readFileByRandomAccess(filename);
177     }
178 }

1 package 天才白痴梦;
2
3 import java.io.BufferedWriter;
4 import java.io.File;
5 import java.io.FileNotFoundException;
6 import java.io.FileOutputStream;
7 import java.io.FileWriter;
8 import java.io.IOException;
9 import java.io.OutputStreamWriter;
10
11 public class JavaIO2 {
12
13     public static void main(String[] args) throws IOException {
14         String Path="E:\\天才白痴梦\\JAVA";
15         File file=new File("E:\\天才白痴梦\\JAVA","BaiYiShaoNian.txt");
16         if (!file.exists()) {
17             try {
18                 file.createNewFile();
19             } catch (IOException e) {
20                 e.printStackTrace();
21             }
22         }
23         /**
24          * Java写入文件的三种方法
25          * */
26         FileOutputStream fos=null;
27         BufferedWriter bw=null;
28         FileWriter fw=null;
29         int value=1000;
30
31         try {
32             fos=new FileOutputStream(new File(Path+"fos.txt"));
33             long begin=System.currentTimeMillis();
34             for (int i=1; i<=value; i++) {
35                 fos.write(5);
36             }
37             long end=System.currentTimeMillis();
38             System.out.println("TheCostTime of FileOutputStream is : " + (end-begin));
39             fos.close();
40
41             bw=new BufferedWriter(new OutputStreamWriter(new FileOutputStream(new File(Path+"br.txt")),"UTF8"));
42             begin=System.currentTimeMillis();
43             for (int i=1; i<=value; i++) {
44                 bw.write(5);
45                 bw.newLine();
46             }
47             bw.close();
48             end=System.currentTimeMillis();
49             System.out.println("TheCostTime of BufferedWriter is : " + (end-begin));
50
51             fw=new FileWriter(Path+"fw.txt");
52             begin=System.currentTimeMillis();
53             for (int i=1; i<=value; i++) {
54                 fw.write(5);
55             }
56             fw.close();
57             end=System.currentTimeMillis();
58             System.out.println("TheCostTime of FileWriter is : " + (end-begin));
59
60
61         } catch (Exception e) {
62             // TODO Auto-generated catch block
63             e.printStackTrace();
64         } finally {
65             try {
66                 fos.close(); //FileOutputStream
67                 bw.close(); //BufferedWriter
68                 fw.close(); //FileWriter
69             } catch (Exception e) {
70                 e.printStackTrace();
71             }
72         }
73
74     }
75 }