fix Size exceeds Integer.MAX_VALUE in File Map

Author: robert

.gitignore

@@ -0,0 +1 @@
+/bin/

src/com/algorithm/digest/DigestUtil.java

@@ -0,0 +1,112 @@
+package com.algorithm.digest;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.math.BigInteger;
+import java.nio.MappedByteBuffer;
+import java.nio.channels.FileChannel.MapMode;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+
+/**
+ * 快速获取文件MD5
+ * 
+ * @author robert
+ *
+ */
+public class DigestUtil {
+	public static String fastDigest(File file) {
+		FileInputStream input = null;
+		try {
+			MessageDigest md = MessageDigest.getInstance("md5");
+			input = new FileInputStream(file);
+			long len = file.length();
+			long start = 0;
+			if (file.length() > 1024 * 1024 * 1024 * 2) {
+				len = 1024 * 1024 * 1024 * 1;
+				start = len;
+			}
+			MappedByteBuffer mb = input.getChannel().map(MapMode.READ_ONLY, 0, len);
+			md.update(mb);
+			if (start != 0) {
+				FileInputStream in = null;
+				byte buffer[] = new byte[1024 * 1024 * 10];
+				try {
+					in = new FileInputStream(file);
+					in.skip(len);
+					int length = 0;
+					while ((length = in.read(buffer)) != -1) {
+						md.update(buffer, 0, length);
+					}
+					in.close();
+				} catch (Exception e) {
+					e.printStackTrace();
+					return null;
+				}
+			}
+			return bytesTohex(md.digest());
+
+		} catch (NoSuchAlgorithmException e) {
+			// TODO Auto-generated catch block
+			e.printStackTrace();
+		} catch (FileNotFoundException e) {
+			// TODO Auto-generated catch block
+			e.printStackTrace();
+		} catch (IOException e) {
+			// TODO Auto-generated catch block
+			e.printStackTrace();
+		} finally {
+			try {
+				if (input != null) {
+					input.close();
+				}
+			} catch (IOException e) {
+				// TODO Auto-generated catch block
+				e.printStackTrace();
+			}
+
+		}
+		return null;
+	}
+
+	public static String getFileMD5(File file) {
+		MessageDigest digest = null;
+		FileInputStream in = null;
+		byte buffer[] = new byte[1024 * 1024 * 10];
+		int len;
+		try {
+			digest = MessageDigest.getInstance("MD5");
+			in = new FileInputStream(file);
+			in.read(buffer, 0, 1);
+			while ((len = in.read(buffer)) != -1) {
+				digest.update(buffer, 0, len);
+			}
+			in.close();
+		} catch (Exception e) {
+			e.printStackTrace();
+			return null;
+		}
+		return bytesTohex(digest.digest());
+	}
+
+	/**
+	 * 字节转换为Stirng
+	 * 
+	 * 快速简单实现方式 BigInteger bigInt = new BigInteger(1, digest.digest()); <br>
+	 * return bigInt.toString(16);
+	 * 
+	 * @param bytes
+	 * @return
+	 */
+	public static String bytesTohex(byte[] bytes) {
+		StringBuffer strbuf = new StringBuffer();
+		for (int i = 0; i < bytes.length; i++) {
+			strbuf.append(Character.forDigit((bytes[i] & 0xf0) >> 4, 16));
+			strbuf.append(Character.forDigit((bytes[i] & 0x0f), 16));
+		}
+		return strbuf.toString();
+
+	}
+}