JDK中的Base64演化流程

Base64就是用来将非ASCII字符的数据转换成ASCII字符的一种方法。

在JDK1.6之前，JDK核心类一直没有Base64的实现类。一般通过反射调用 Sun/Oracle JDK 里面的 sun.misc.BASE64Encoder 和 sun.misc.BASE64Decoder，使用它的优点就是不需要依赖第三方类库，缺点就是可能在未来版本会被删除（用maven编译会发出警告），而且性能不佳。

JDK1.6中添加了另一个Base64的实现，javax.xml.bind.DatatypeConverter两个静态方法parseBase64Binary 和 printBase64Binary，隐藏在javax.xml.bind包下面。

在Java 8在java.util包下面实现了Base64编解码API，而且性能不俗，API也简单易懂。该Base64有3个Encoder，分别是“标准Encoder”、“urlEncoder”、“mimeEncoder”，它们编码出的字符串基本相同，只有在原始字符串是以“某种协议://……”开头时，后续的问号（”？”）编码的结果才会有所不同 —— “标准Encoder”和“mimeEncoder”将其编码为“/”，而“urlEncoder”却将编码为“_”。其它情况发现编码出的结果暂时都是一样的。

测试代码

package com.demo.test;
import java.util.Arrays;
import java.util.Base64;
import java.util.Base64.Encoder;
import java.util.UUID;

public class Base64Demo {
    public static void main(String[] args) {

        String str = "~!@#$%^&*()_+{}:\"|<>?`-=[];'\\,./'";
        printBase64Str(str);

        str = "http://localhost:8080/index.html?word1=xxx&word2=xxx";
        printBase64Str(str);

        str = "http://localhost:8080/index.html?";
        printBase64Str(str);

        str = "file://localhost:8080/index.html?";
        printBase64Str(str);

        str = "file:///localhost:8080/index.html?";
        printBase64Str(str);

        str = "localhost:8080/index.html?";
        printBase64Str(str);

        str = UUID.randomUUID().toString();
        printBase64Str(str);

        str = "中文测试";
        printBase64Str(str);
    }

    private static void printBase64Str(String str) {
        System.out.println(str);
        byte[] buffer = str.getBytes();
        Encoder encoder = Base64.getEncoder();
        Encoder urlEncoder = Base64.getUrlEncoder();
        Encoder mimeEncoder = Base64.getMimeEncoder();
        String result = encoder.encodeToString(buffer);
        String urlResult = urlEncoder.encodeToString(buffer);
        String mimeResult = mimeEncoder.encodeToString(buffer);
        System.out.println(result);
        System.out.println(urlResult);
        System.out.println(mimeResult);
        if(!Arrays.equals(buffer, Base64.getDecoder().decode(result))) {
            System.err.println("decode not equal");
        }
        if(!Arrays.equals(buffer, Base64.getUrlDecoder().decode(urlResult))) {
            System.err.println("decode not equal");
        }
        if(!Arrays.equals(buffer, Base64.getMimeDecoder().decode(mimeResult))) {
            System.err.println("decode not equal");
        }
        System.out.println();
    }
}

运行输出

~!@#$%^&*()_+{}:"|<>?`-=[];'\,./'
fiFAIyQlXiYqKClfK3t9OiJ8PD4/YC09W107J1wsLi8n
fiFAIyQlXiYqKClfK3t9OiJ8PD4_YC09W107J1wsLi8n
fiFAIyQlXiYqKClfK3t9OiJ8PD4/YC09W107J1wsLi8n

http://localhost:8080/index.html?word1=xxx&word2=xxx
aHR0cDovL2xvY2FsaG9zdDo4MDgwL2luZGV4Lmh0bWw/d29yZDE9eHh4JndvcmQyPXh4eA==
aHR0cDovL2xvY2FsaG9zdDo4MDgwL2luZGV4Lmh0bWw_d29yZDE9eHh4JndvcmQyPXh4eA==
aHR0cDovL2xvY2FsaG9zdDo4MDgwL2luZGV4Lmh0bWw/d29yZDE9eHh4JndvcmQyPXh4eA==

http://localhost:8080/index.html?
aHR0cDovL2xvY2FsaG9zdDo4MDgwL2luZGV4Lmh0bWw/
aHR0cDovL2xvY2FsaG9zdDo4MDgwL2luZGV4Lmh0bWw_
aHR0cDovL2xvY2FsaG9zdDo4MDgwL2luZGV4Lmh0bWw/

file://localhost:8080/index.html?
ZmlsZTovL2xvY2FsaG9zdDo4MDgwL2luZGV4Lmh0bWw/
ZmlsZTovL2xvY2FsaG9zdDo4MDgwL2luZGV4Lmh0bWw_
ZmlsZTovL2xvY2FsaG9zdDo4MDgwL2luZGV4Lmh0bWw/

file:///localhost:8080/index.html?
ZmlsZTovLy9sb2NhbGhvc3Q6ODA4MC9pbmRleC5odG1sPw==
ZmlsZTovLy9sb2NhbGhvc3Q6ODA4MC9pbmRleC5odG1sPw==
ZmlsZTovLy9sb2NhbGhvc3Q6ODA4MC9pbmRleC5odG1sPw==

localhost:8080/index.html?
bG9jYWxob3N0OjgwODAvaW5kZXguaHRtbD8=
bG9jYWxob3N0OjgwODAvaW5kZXguaHRtbD8=
bG9jYWxob3N0OjgwODAvaW5kZXguaHRtbD8=

d1a2e1be-6928-465a-b7c9-1d67e22d1536
ZDFhMmUxYmUtNjkyOC00NjVhLWI3YzktMWQ2N2UyMmQxNTM2
ZDFhMmUxYmUtNjkyOC00NjVhLWI3YzktMWQ2N2UyMmQxNTM2
ZDFhMmUxYmUtNjkyOC00NjVhLWI3YzktMWQ2N2UyMmQxNTM2

中文测试
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