append的方式写文件，FileWriter如何实现??

summerG

append的方式写文件，FileWriter如何实现??

seth

看看JDK 文档吧
FileWriter out = new FileWriter ("file name", true)

cinc

以前写的一段代码，看 append() 方法：

1. 
   
2. import java.io.File;
   
3. import java.io.FileWriter;
   
4. import java.io.PrintWriter;
   
5. import java.io.IOException;
   
6. 
   
7. /**
   
8. * <p>;
   
9. * A simple log writer, append a line to a text file
   
10. *
    
11. * Note: the log file should be created manually now.
    
12. * </p>;
    
13. *
    
14. * @author cinc
    
15. */
    
16. public class LogWriter{
    
17.     /**
    
18.      * filename of the log file
    
19.      */
    
20.     protected String filename;
    
21.     /**
    
22.      * the log file
    
23.      */
    
24.     protected File file;
    
25.     /**
    
26.      * the file writer
    
27.      */
    
28.     protected FileWriter fWriter;
    
29.     /**
    
30.      * the print writer (we can invoke function : println(String))
    
31.      */
    
32.     protected PrintWriter pWriter;
    
33. 
    
34.     /**
    
35.      * Constructor
    
36.      *
    
37.      * @param        filename        the filename of the log
    
38.      *
    
39.      */
    
40.     public LogWriter(String filename) throws IOException{
    
41.         this.filename = filename;
    
42.         file = new File(filename);
    
43.     }
    
44. 
    
45.     /**
    
46.      * append a new line to the log file, also output it to console
    
47.      *
    
48.      * @param      log          the string to write to file
    
49.      *
    
50.      */
    
51.     public synchronized void append(String log){
    
52.         fWriter = null;
    
53.         pWriter = null;
    
54.         try{
    
55.             fWriter = new FileWriter(file, true);
    
56.             pWriter = new PrintWriter(fWriter);
    
57.             // append to log file
    
58.             pWriter.println(log);
    
59.             // output it to console
    
60.             System.out.println(log);
    
61.         }catch (IOException e){
    
62.             System.out.println ("Error Writing log file: " + e);
    
63.         }finally{
    
64.             try{
    
65.                 if (pWriter != null){
    
66.                     pWriter.close();
    
67.                 }
    
68.                 if (fWriter != null){
    
69.                     fWriter.close();
    
70.                 }
    
71.             }catch (IOException e){}
    
72.         }
    
73.     }
    
74. 
    
75.     /**
    
76.      * Return the length of the log file
    
77.      *
    
78.      * @return       the length of the log file
    
79.      *
    
80.      */
    
81.     public long getLength(){
    
82.         return file.length();
    
83.     }
    
84. 
    
85.     /**
    
86.      * append a new line to the log file, also output it to console
    
87.      *
    
88.      * @param      obj          the object to write to file
    
89.      *
    
90.      */
    
91.     public void append(Object obj) throws IOException{
    
92.         append(obj.toString());
    
93.     }
    
94. 
    
95. }
    
96. 
    

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