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 digestprivate 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;}