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itemprop="author" itemscope itemtype="http://schema.org/Person"><meta itemprop="name" content="MrBird"><meta itemprop="description" content=""><meta itemprop="image" content="/images/blogImage.jpg"></span><span hidden itemprop="publisher" itemscope itemtype="http://schema.org/Organization"><meta itemprop="name" content="MrBird"></span><header class="post-header"><h2 class="post-title" itemprop="name headline">Java Base64算法</h2><div class="post-meta"><span class="post-time"><span class="post-meta-item-icon"><i class="fa fa-calendar-o"></i> </span><span class="post-meta-item-text"></span> <time title="创建于" itemprop="dateCreated datePublished" datetime="2020-04-21T14:24:20+08:00">2020-04-21 </time></span><span></span> <span class="post-meta-divider">|</span> <span class="page-pv"><i class="fa fa-laptop"></i> Visit count <span class="busuanzi-value" id="busuanzi_value_page_pv"></span></span></div></header><div class="post-body" itemprop="articleBody"><p>Base64算法并不是加密算法，它的出现是为了解决ASCII码在传输过程中可能出现乱码的问题。Base64是网络上最常见的用于传输8bit字节码的可读性编码算法之一。可读性编码算法不是为了保护数据的安全性，而是为了可读性。可读性编码不改变信息内容，只改变信息内容的表现形式。Base64使用了64种字符：大写A到Z、小写a到z、数字0到9、“+”和“/”，故得此名。</p><a id="more"></a><h2 id="储备知识Byte和bit"><a href="#储备知识Byte和bit" class="headerlink" title="储备知识Byte和bit"></a>储备知识Byte和bit</h2><p>Byte：字节，数据存储的基本单位；</p><p>bit：比特，也叫位，一个位只能存储0或者1。</p><p>关系：1Byte = 8bit。</p><p>一个英文字符占1个字节，8位：</p><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Test</span></span><br><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">demo1</span><span class="params">()</span> </span>{</span><br><span class="line"> String a = <span class="string">"a"</span>;</span><br><span class="line"> <span class="keyword">byte</span>[] bytes = a.getBytes();</span><br><span class="line"> <span class="keyword">for</span> (<span class="keyword">byte</span> b : bytes) {</span><br><span class="line"> System.out.println(b);</span><br><span class="line"> System.out.println(Integer.toBinaryString(b));</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p></p><p>程序输出：</p><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">97</span><br><span class="line">1100001</span><br></pre></td></tr></table></figure><p></p><p>一个中文字符在不同编码下所占的字节数不同：</p><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br></pre></td><td class="code"><pre><span class="line"><span class="meta">@Test</span></span><br><span class="line"><span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">demo2</span><span class="params">()</span> <span class="keyword">throws</span> UnsupportedEncodingException </span>{</span><br><span class="line"> String a = <span class="string">"鸟"</span>;</span><br><span class="line"> <span class="keyword">byte</span>[] utf8Bytes = a.getBytes(<span class="string">"utf-8"</span>);</span><br><span class="line"> <span class="keyword">for</span> (<span class="keyword">byte</span> b : utf8Bytes) {</span><br><span class="line"> System.out.print(b);</span><br><span class="line"> System.out.print(<span class="string">" "</span>);</span><br><span class="line"> System.out.println(Integer.toBinaryString(b));</span><br><span class="line"> }</span><br><span class="line"> System.out.println();</span><br><span class="line"> <span class="keyword">byte</span>[] gbkBytes = a.getBytes(<span class="string">"gbk"</span>);</span><br><span class="line"> <span class="keyword">for</span> (<span class="keyword">byte</span> b : gbkBytes) {</span><br><span class="line"> System.out.print(b);</span><br><span class="line"> System.out.print(<span class="string">" "</span>);</span><br><span class="line"> System.out.println(Integer.toBinaryString(b));</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p></p><p>程序输出：</p><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br></pre></td><td class="code"><pre><span class="line">-23 11111111111111111111111111101001</span><br><span class="line">-72 11111111111111111111111110111000</span><br><span class="line">-97 11111111111111111111111110011111</span><br><span class="line"></span><br><span class="line">-60 11111111111111111111111111000100</span><br><span class="line">-15 11111111111111111111111111110001</span><br></pre></td></tr></table></figure><p></p><p>所以在UTF-8编码下，一个中文占3个字节；在GBK编码下，一个中文占2个字节。</p><h2 id="Base64编码原理"><a href="#Base64编码原理" class="headerlink" title="Base64编码原理"></a>Base64编码原理</h2><p>Base64编码表：</p><table><tbody><tr><td><div><b>索引</b></div></td><td><div><b>对应字符</b></div></td><td><div><b>索引</b></div></td><td><div><b>对应字符</b></div></td><td><div><b>索引</b></div></td><td><div><b>对应字符</b></div></td><td><div><b>索引</b></div></td><td><div><b>对应字符</b></div></td></tr><tr><td><div>0</div></td><td><div><b>A</b></div></td><td><div>17</div></td><td><div><b>R</b></div></td><td><div>34</div></td><td><div><b>i</b></div></td><td><div>51</div></td><td><div><b>z</b></div></td></tr><tr><td><div>1</div></td><td><div><b>B</b></div></td><td><div>18</div></td><td><div><b>S</b></div></td><td><div>35</div></td><td><div><b>j</b></div></td><td><div>52</div></td><td><div><b>0</b></div></td></tr><tr><td><div>2</div></td><td><div><b>C</b></div></td><td><div>19</div></td><td><div><b>T</b></div></td><td><div>36</div></td><td><div><b>k</b></div></td><td><div>53</div></td><td><div><b>1</b></div></td></tr><tr><td><div>3</div></td><td><div><b>D</b></div></td><td><div>20</div></td><td><div><b>U</b></div></td><td><div>37</div></td><td><div><b>l</b></div></td><td><div>54</div></td><td><div><b>2</b></div></td></tr><tr><td><div>4</div></td><td><div><b>E</b></div></td><td><div>21</div></td><td><div><b>V</b></div></td><td><div>38</div></td><td><div><b>m</b></div></td><td><div>55</div></td><td><div><b>3</b></div></td></tr><tr><td><div>5</div></td><td><div><b>F</b></div></td><td><div>22</div></td><td><div><b>W</b></div></td><td><div>39</div></td><td><div><b>n</b></div></td><td><div>56</div></td><td><div><b>4</b></div></td></tr><tr><td><div>6</div></td><td><div><b>G</b></div></td><td><div>23</div></td><td><div><b>X</b></div></td><td><div>40</div></td><td><div><b>o</b></div></td><td><div>57</div></td><td><div><b>5</b></div></td></tr><tr><td><div>7</div></td><td><div><b>H</b></div></td><td><div>24</div></td><td><div><b>Y</b></div></td><td><div>41</div></td><td><div><b>p</b></div></td><td><div>58</div></td><td><div><b>6</b></div></td></tr><tr><td><div>8</div></td><td><div><b>I</b></div></td><td><div>25</div></td><td><div><b>Z</b></div></td><td><div>42</div></td><td><div><b>q</b></div></td><td><div>59</div></td><td><div><b>7</b></div></td></tr><tr><td><div>9</div></td><td><div><b>J</b></div></td><td><div>26</div></td><td><div><b>a</b></div></td><td><div>43</div></td><td><div><b>r</b></div></td><td><div>60</div></td><td><div><b>8</b></div></td></tr><tr><td><div>10</div></td><td><div><b>K</b></div></td><td><div>27</div></td><td><div><b>b</b></div></td><td><div>44</div></td><td><div><b>s</b></div></td><td><div>61</div></td><td><div><b>9</b></div></td></tr><tr><td><div>11</div></td><td><div><b>L</b></div></td><td><div>28</div></td><td><div><b>c</b></div></td><td><div>45</div></td><td><div><b>t</b></div></td><td><div>62</div></td><td><div><b>+</b></div></td></tr><tr><td><div>12</div></td><td><div><b>M</b></div></td><td><div>29</div></td><td><div><b>d</b></div></td><td><div>46</div></td><td><div><b>u</b></div></td><td><div>63</div></td><td><div><b>/</b></div></td></tr><tr><td><div>13</div></td><td><div><b>N</b></div></td><td><div>30</div></td><td><div><b>e</b></div></td><td><div>47</div></td><td><div><b>v</b></div></td><td></td><td></td></tr><tr><td><div>14</div></td><td><div><b>O</b></div></td><td><div>31</div></td><td><div><b>f</b></div></td><td><div>48</div></td><td><div><b>w</b></div></td><td></td><td></td></tr><tr><td><div>15</div></td><td><div><b>P</b></div></td><td><div>32</div></td><td><div><b>g</b></div></td><td><div>49</div></td><td><div><b>x</b></div></td><td></td><td></td></tr><tr><td><div>16</div></td><td><div><b>Q</b></div></td><td><div>33</div></td><td><div><b>h</b></div></td><td><div>50</div></td><td><div><b>y</b></div></td><td></td><td></td></tr></tbody></table><p>Base64编码的过程：</p><ol><li>将字符串转换为字符数组；</li><li>将每个字符转换为ASCII码；</li><li>将ASCII码转换为8bit二进制码；</li><li>然后每3个字节为一组（一个字节为8个bit，所以每组24个bit）；</li><li>将每组的24个bit分为4份，每份6个bit；</li><li>在每6个bit前补0，补齐8bit（前面补0不影响数值大小）；</li><li>然后将每8bit转换为10进制数，根据上面的Base64编码表进行转换。</li></ol><div class="note info">上面步骤中，为什么要将每组24个bit分为4份，每份6个bit呢？因为6bit的最大值为111111，转换为十进制为63，所以6bit的取值范围为0~63，这和base64编码表长度一致。</div><p>根据上面的过程，我们来举个例子：现要对hello这个字符串进行Base64编码，过程如下：</p><ol><li>hello转换为字符数组：h e l l o；</li><li>对应的ASCII码为：104 101 108 108 111；</li><li>转换为8bit二进制数：01101000 01100101 01101100 01101100 01101111</li><li>分组，每组24个bit（不足24个bit的用00000000补齐）： 011010000110010101101100 011011000110111100000000；</li><li>每组24bit分为4份，每份6bit：011010 000110 010101 101100 011011 000110 111100 000000；</li><li>在每6个bit前补0，补齐8bit：00011010 00000110 00010101 00101100 00011011 00000110 00111100 00000000；</li><li>将每8bit转换为10进制数：26 6 21 44 27 6 60 0</li><li>从上面Base64编码表中找到十进制数对应的字符（末尾的0并不是A，而是用=等号补位）：a G V s b G 8 =</li></ol><p>所以hello经过Base64编码的结果为aGVsbG8=</p><p>我们可以用代码验证下（JDK8开始已经提供了Base64的实现）：</p><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> org.junit.Test;</span><br><span class="line"><span class="keyword">import</span> java.util.Base64;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Base64Test</span> </span>{</span><br><span class="line"></span><br><span class="line"> <span class="meta">@Test</span></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">demo1</span><span class="params">()</span> </span>{</span><br><span class="line"> System.out.println(Base64.getEncoder().encodeToString(<span class="string">"hello"</span>.getBytes()));</span><br><span class="line"> }</span><br><span class="line">}</span><br></pre></td></tr></table></figure><p>程序输出也是aGVsbG8=</p><h2 id="URL-Base64算法"><a href="#URL-Base64算法" class="headerlink" title="URL Base64算法"></a>URL Base64算法</h2><p>Base64编码值通过URL传输会出现问题，因为Base64编码中的“+”和“/”符号是不允许出现在URL中的。同样，符号“=”用做参数分隔符，也不允许出现在URL中，根据RFC 4648中的建议，“~”和“.”符都有可能替代“=”符号。但“~”符号与文件系统相冲突，不能使用；如果使用“.”符号，某些文件系统认为该符号连续出现两次则为错误。</p><p>所以common codec包下的URL Base64算法舍弃了填充符，使用了不定长URL Base64编码。</p><p>引入common codec依赖包：</p><figure class="highlight xml"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br></pre></td><td class="code"><pre><span class="line"><span class="tag"><<span class="name">dependency</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">groupId</span>></span>commons-codec<span class="tag"></<span class="name">groupId</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">artifactId</span>></span>commons-codec<span class="tag"></<span class="name">artifactId</span>></span></span><br><span class="line"> <span class="tag"><<span class="name">version</span>></span>1.14<span class="tag"></<span class="name">version</span>></span></span><br><span class="line"><span class="tag"></<span class="name">dependency</span>></span></span><br></pre></td></tr></table></figure><p></p><p>举个例子：</p><figure class="highlight java"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br></pre></td><td class="code"><pre><span class="line"><span class="keyword">import</span> org.apache.commons.codec.binary.Base64;</span><br><span class="line"><span class="keyword">import</span> org.junit.Test;</span><br><span class="line"></span><br><span class="line"><span class="keyword">public</span> <span class="class"><span class="keyword">class</span> <span class="title">Base64Test</span> </span>{</span><br><span class="line"></span><br><span class="line"> <span class="meta">@Test</span></span><br><span class="line"> <span class="function"><span class="keyword">public</span> <span class="keyword">void</span> <span class="title">demo1</span><span class="params">()</span> </span>{</span><br><span class="line"> String value = <span class="string">"hello"</span>;</span><br><span class="line"> System.out.println(Base64.encodeBase64String(value.getBytes()));</span><br><span class="line"> System.out.println(Base64.encodeBase64URLSafeString(value.getBytes()));</span><br><span class="line"> }</span><br><span class="line"></span><br><span class="line">}</span><br></pre></td></tr></table></figure><p></p><p>输出如下：</p><figure class="highlight plain"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br></pre></td><td class="code"><pre><span class="line">aGVsbG8=</span><br><span class="line">aGVsbG8</span><br></pre></td></tr></table></figure><p></p><script>$(".post-body a").not(".thispage").addClass("ignore-href").attr("target","_blank")</script></div><div></div><div><div style="padding:10px 0;margin:20px auto;width:90%;text-align:center;color:#878787" id="reward-div"><div>请作者喝瓶肥宅水🥤</div><button id="rewardButton" style="margin-top:10px" disable="enable" onclick='var e=document.getElementById("QR");"none"===e.style.display?e.style.display="block":e.style.display="none"'><span 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