从inputStream中读取指定长度的字节

Java 中如何从InputStream中读取指定长度的字节呢？

代码如下：

Java代码  

1. /*** 
2.      * 从输入流获取字节数组,当文件很大时，报java.lang.OutOfMemoryError: Java heap space 
3.      *  
4.      * @since 2014-02-19 
5.      * @param br_right 
6.      * @param length2 
7.      * @return 
8.      * @throws IOException 
9.      */  
10.     public static byte[] readBytesFromInputStream(InputStream br_right,  
11.             int length2) throws IOException {  
12.         int readSize;  
13.         byte[] bytes = null;  
14.         bytes = new byte[length2];  
15.   
16.         long length_tmp = length2;  
17.         long index = 0;// start from zero  
18.         while ((readSize = br_right.read(bytes, (int) index, (int) length_tmp)) != -1) {  
19.             length_tmp -= readSize;  
20.             if (length_tmp == 0) {  
21.                 break;  
22.             }  
23.             index = index + readSize;  
24.         }  
25.         return bytes;  
26.     }  
27. /*** 
28.      * 读取指定长度的字节 
29.      * @since 2014-02-27 
30.      * @param ins 
31.      * @param sumLeng : 要读取的字节数 
32.      * @return 
33.      * @throws IOException 
34.      */  
35.     public static byte[]readBytesFromGzipInputStream(GZIPInputStream ins,long sumLeng) throws IOException{  
36.         byte[] fileNameBytes = new byte[(int) sumLeng];  
37.         int fileNameReadLength=0;  
38.         int hasReadLength=0;//已经读取的字节数  
39.         while((fileNameReadLength=ins.read(fileNameBytes,hasReadLength,(int)sumLeng-hasReadLength))>0){  
40.             hasReadLength=hasReadLength+fileNameReadLength;  
41.         }  
42.         return fileNameBytes;  
43.     }  
44. /*** 
45.      * read char array from inputstream according to specified length. 
46.      *  
47.      * @param file 
48.      * @param ins 
49.      * @param length2 
50.      *            :要读取的字符总数 
51.      * @throws IOException 
52.      */  
53.     public static char[] getCharsFromInputStream(BufferedReader br_right,  
54.             int length2) throws IOException {  
55.         int readSize;  
56.         char[] chars = null;  
57.         chars = new char[length2];  
58.   
59.         long length_tmp = length2;  
60.         long index = 0;// start from zero  
61.         while ((readSize = br_right.read(chars, (int) index, (int) length_tmp)) != -1) {  
62.             length_tmp -= readSize;  
63.             if (length_tmp == 0) {  
64.                 break;  
65.             }  
66.             index = index + readSize;// 写入字符数组的offset（偏移量）  
67.         }  
68.         return chars;  
69.     }  
70.   
71. /*** 
72.      * 从文件中读取指定长度的字符（注意：不是字节） 
73.      *  
74.      * @param file 
75.      * @param length2 
76.      * @return 
77.      * @throws IOException 
78.      */  
79.     public static char[] getCharsFromFile(File file, int length2)  
80.             throws IOException {  
81.         FileInputStream fin = new FileInputStream(file);  
82.         InputStreamReader inr = new InputStreamReader(fin);  
83.         BufferedReader br = new BufferedReader(inr);  
84.         return getCharsFromInputStream(br, length2);  
85.     }  
86. private static byte[] readDataFromLength(HttpURLConnection huc,  
87.             int contentLength) throws Exception {  
88.   
89.         InputStream in = huc.getInputStream();  
90.         BufferedInputStream bis = new BufferedInputStream(in);  
91.   
92.         // 数据字节数组  
93.         byte[] receData = new byte[contentLength];  
94.   
95.         // 已读取的长度  
96.         int readAlreadyLength = 0;  
97.   
98.         // while ((readAlreadyLength+= bis.read(receData, readAlreadyLength,  
99.         // contentLength-readAlreadyLength))< contentLength) {  
100.         // System.out.println("right");  
101.         // }  
102.         while ((readAlreadyLength = readAlreadyLength  
103.                 + bis.read(receData, readAlreadyLength, contentLength  
104.                         - readAlreadyLength)) < contentLength) {  
105.         }  
106.         // System.out.println("readLength=" + readLength);  
107.         return receData;  
108.     }  

参考我的另外一篇博客：http://hw1287789687.iteye.com/blog/2019425