Io優化
Java中的IO的性能優化 如果只是簡單的文件拷貝，下邊兩種方法也不錯
在使用IO的時候注意一下細節，能使性能得到很大的優化.
首先讀寫大文件，使用Buffer是肯定的了,使用方法，有下邊兩個
方法一：
2 
public static void test1(String fileName) {
3 
long start = System.currentTimeMillis();
4 
try {
5 FileInputStream fis = new FileInputStream(fileName);
6 BufferedReader br = new BufferedReader( new InputStreamReader(fis) );
7 StringBuffer sb = new StringBuffer();
8 String str;
9 while ((str = br.readLine()) != null ) {
10 sb.append(str);
11 
} </span>
12 } </span> catch (IOException e) {
13 } </span>
14 long end = System.currentTimeMillis();
15 long time = end - start;
16 System.out.println(time);
17 
} </span>
18 方法二：
19 public static void test2(String fileName) {
20 long start = System.currentTimeMillis();
21 try {
22 FileInputStream fis = new FileInputStream(fileName);
23 byte buf[] = new byte [ 8192 ];
24 int n;
25 StringBuffer sb = new StringBuffer();
26 while ((n = fis.read(buf)) != - 1 ) {
27 sb.append(buf);
28 } </span>
29 fis.close();
30 } </span> catch (IOException e) {
31 } </span>
32 long end = System.currentTimeMillis();
33 long time = end - start;
34 System.out.println(time);
35 }</span>
方法一1937ms
方法二47ms
測試結果相差大概50倍左有，很大。
而我平時的習慣是方法一。問題主要出在readLine()上。 public static void test3() {
2 String cmd = " copy d:/out1.txt out2.txt " ;
3 try {
4 Runtime.getRuntime().exec(cmd);
5 } </span> catch (Exception e) {
6 e.printStackTrace();
7 } </span>
8 } </span>
9 public static void test4() {
10 String inFileName = " d:/out1.txt " ;
11 String outFileName = " d:/out2.txt " ;
12 long start = System.currentTimeMillis();
13 try {
14 File inFile = new File(inFileName);
15 File outFile = new File(outFileName);
16 RandomAccessFile inRaf = new RandomAccessFile(inFile, " r " );
17 RandomAccessFile outRaf = new RandomAccessFile(outFile, " rw " );
18 FileChannel infc = inRaf.getChannel();
19 FileChannel outfc = outRaf.getChannel();
20 infc.transferTo( 0 , inFile.length(),outfc );
21 infc.close();
22 outfc.close();
23 } </span> catch (Exception e) {
24 e.printStackTrace();
25 } </span>
26 long end = System.currentTimeMillis();
27 long time = end - start;
28 System.out.println(time);</span></span>
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