MD5和Base64

使用apache的commons-codec jar包进行Base64编码/解码，md5加密

package base64; import java.io.UnsupportedEncodingException; import org.apache.commons.codec.binary.Base64; import org.apache.commons.codec.digest.DigestUtils; public class MD5Demo { public static void main(String[] args) { String str = "你好，很高兴认识你！"; try { String encode = Base64.encodeBase64String(str.getBytes("utf-8")); System.out.println(encode); String decode = new String(Base64.decodeBase64(encode), "utf-8"); System.out.println(decode); } catch (UnsupportedEncodingException e) { e.printStackTrace(); } String code = Base64.encodeBase64String(DigestUtils.md5(str)); System.out.println(code); } }

输出结果分别为

5L2g5aW977yM5b6I6auY5YW06K6k6K+G5L2g77yB 你好，很高兴认识你！ L9aMgawEobXiPtOoDBXsrg==

JDK本身也自带Base64的类，不过并不太好找 com.sun.org.apache.xerces.internal.impl.dv.util.Base64是一个，好像还有其他的。JDK1.8则有个java.util.Base64类。

JDK本身也自带MD5摘要算法功能，java.security.MessageDigest;

public static void main(String[] args) { String str = "你好，很高兴认识你！"; try { byte[] data = str.getBytes("utf-8"); MessageDigest md = MessageDigest.getInstance("md5"); byte[] md5 = md.digest(data); // md.update(data); // byte[] md5 = md.digest(); String code = Base64.encodeBase64String(md5); System.out.println(code); } catch (Exception e) { e.printStackTrace(); throw new RuntimeException("加密失败", e); } }

其中md.digest(data);等同于md.update(data);md.digest();其内部调用关系如下：

public byte[] digest(byte[] input) { update(input); return digest(); }

另外不能连续调用update(byte[] input)，会影响算法结果，即：

{ /*错误*/ md.update(data); md.update(data); md.digest(); } { /*错误*/ md.update(data); md.digest(data); } { /*正确*/ md.update(data); md.digest(); } { /*正确*/ md.update(data); }

MessageDigest源码中有个state属性，update会更改其属性，digest后会改回默认，大概是因为这个属性的原因吧，engineUpdate()方法的源码没有找到，不清楚state是否真的对其造成影响，但是多次update后得到的md5并不一样

// The state of this digest private static final int INITIAL = 0; private static final int IN_PROGRESS = 1; private int state = INITIAL; /** * Updates the digest using the specified byte. * * @param input the byte with which to update the digest. */ public void update(byte input) { engineUpdate(input); state = IN_PROGRESS; } /** * Completes the hash computation by performing final operations * such as padding. The digest is reset after this call is made. * * @return the array of bytes for the resulting hash value. */ public byte[] digest() { /* Resetting is the responsibility of implementors. */ byte[] result = engineDigest(); state = INITIAL; return result; }