java文件的I/O

【原创】

java文件的I/O操作，简单来说就是向文件中写入数据以及从文件中读出数据，这是我们平日做的最多的操作，这里给出两种文件I/O操作，当然还有许多的操作方法，各种流的使用，可谓是高深莫测；不管了，直接怼代码：

 1 package com.jiajia.filedemo;
 2 
 3 import java.io.BufferedReader;
 4 import java.io.BufferedWriter;
 5 import java.io.File;
 6 import java.io.FileInputStream;
 7 import java.io.FileOutputStream;
 8 import java.io.FileReader;
 9 import java.io.FileWriter;
10 import java.io.InputStreamReader;
11 import java.io.OutputStreamWriter;
12 
13 public class Demo_1 {
14         public static void main(String[] args) throws Exception{
15         String filename_input = "/Users/fanjiajia/Desktop/temp";
16         String filename_output = "/Users/fanjiajia/Desktop/temp2.txt";//若temp1不存在，他会自己给你创建一个
17         String str = read_1(filename_input);
18         System.out.println(str);
19         writer_2(str, filename_output);
20     }
21     /**
22      *文件读取方法一
23      * @param filename
24      * @return
25      * @throws Exception
26      */
27     public static String read_1(String filename) throws Exception{
28         File f = new File(filename);
29         FileInputStream f_in = new FileInputStream(f);
30         InputStreamReader isr = new InputStreamReader(f_in);
31         BufferedReader buf_reader = new BufferedReader(isr); 
32         String s;
33         StringBuilder sb = new StringBuilder();
34         while((s=buf_reader.readLine())!=null){
35             sb.append(s+"
");
36         }
37         buf_reader.close();
38         isr.close();
39         f_in.close();
40         return sb.toString();
41     }
42     /**
43      * 文件读取方法二
44      * @param filename
45      * @return
46      * @throws Exception
47      */
48     public static String read_2(String filename) throws Exception {
49         FileReader filereader = new FileReader(filename);
50         BufferedReader in = new BufferedReader(filereader);
51         String s ;
52         StringBuilder sb = new StringBuilder();
53         while((s=in.readLine())!=null){
54             sb.append(s+"
");
55         }
56         in.close();
57         filereader.close();
58         return sb.toString();
59     }
60 
61     /**
62      * 文件写入方法一
63      * @param str
64      * @param filename
65      * @throws Exception
66      */
67     public static void writer_1(String str,String filename    ) throws Exception{
68         //将给定的字符串输出到filename文件中
69         FileWriter f_writer = new FileWriter(filename);
70         BufferedWriter buf_writer = new BufferedWriter(f_writer);
71         buf_writer.write(str);
72         buf_writer.close();
73         f_writer.close();
74     }
75     /**
76      * 文件写入方法二
77      * @param str
78      * @param filename
79      * @throws Exception
80      */
81     public static void writer_2(String str,String filename) throws Exception{
82         File f = new File(filename);
83         FileOutputStream f_os = new FileOutputStream(f);
84         OutputStreamWriter os  = new OutputStreamWriter(f_os); 
85         BufferedWriter buf_writer = new BufferedWriter(os);
86         buf_writer.write(str);
87         buf_writer.close();
88         os.close();
89         f_os.close();
90     }
91 }

很明显直接使用FileReader 和 FileWriter这两个类并结合BufferedReader／BufferedWriter很方便

其实FileWriter类的对象w直接就可以write，并且在创建是=时候，如果是new FileWriter（。。。，true）；第二个参数为true的话，便是在文件末尾写；