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在Java中逐行比较两个不同的文件

在本文中，我们将比较系统中保存的两个不同的文本文件。我们会逐行检查每个文本文件，通过比较我们可以找出异同。

让我们来看看如何使用Java编程语言来实现它。

向您展示一些实例

实例1

下图描绘了两个具有相同内容的不同文本文件，因此输出将是两个具有相同内容的文件。

实例2

下面表示两个文件，假设是file1.txt和file2.txt，以及它们的内容。

文件1.txt

This is amazing.
Java Language.

file2.txt

This is amazing.
Python Language.

在这里，我们可以注意到两个文件在第 2 行有不同的内容。由于文件 1，第 2 行包含“Java 语言”，文件 2，第 2 行包含“Python 语言”

算法

  • 步骤 1 − 创建reader1和reader2作为两个BufferedReader对象，并使用它们逐行读取两个输入文本文件。

  • 第 2 步 - 创建两个变量。首先，创建一个名为“areEqual”的布尔变量并将其初始化为 true。其次，创建一个名为“lineNum”的 int 变量并将其初始化为 1。areEqual 是一个标志变量，最初设置为 true，当输入文件的内容不同时更改为 false。行数将保存在 lineNum 中。

  • 步骤 3 - 将文件 1 的内容读入第 1 行，将文件 2 的内容读入第 2 行。

  • 第四步 - 将文件file1和file2中的行分别读入line1和line2，直到两个文件都被读取完毕。如果line1或line2为空，则将"areEqual"设置为false。

  • 步骤 5 − 如果 areEqual 为真，则声明两个文件的内容相同。如果 areEqual 的值为假，则声明文件的内容不同。

  • 第 6 步 - 关闭资源。

多种方法

我们通过不同的方式提供了解决方案。

  • 通过使用 BufferedReader 类

  • 通过使用内存映射文件

逐一查看程序及其输出。

方法 1：使用 BufferedReader 类

示例

在这种方法中，您将创建BufferedReader类的对象，并使用内置的readLine()方法读取两个文件的内容并进行比较。

<span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token class-name">BufferedReader</span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token class-name">FileReader</span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token class-name">IOException</span><span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Main</span><span class="token punctuation">{</span>   
   <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">IOException</span><span class="token punctuation">{</span>   

   <span class="token class-name">BufferedReader</span> reader1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedReader</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileReader</span><span class="token punctuation">(</span><span class="token string">"E:\file1.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>  
   <span class="token class-name">BufferedReader</span> reader2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">BufferedReader</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">FileReader</span><span class="token punctuation">(</span><span class="token string">"E:\file2.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
      <span class="token class-name">String</span> line1 <span class="token operator">=</span> reader1<span class="token punctuation">.</span><span class="token function">readLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>    
      <span class="token class-name">String</span> line2 <span class="token operator">=</span> reader2<span class="token punctuation">.</span><span class="token function">readLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
      <span class="token keyword">int</span> lineNum <span class="token operator">=</span> <span class="token number">1</span><span class="token punctuation">;</span>  
      <span class="token keyword">boolean</span> areEqual <span class="token operator">=</span> <span class="token boolean">true</span><span class="token punctuation">;</span>
      <span class="token keyword">while</span> <span class="token punctuation">(</span>line1 <span class="token operator">!=</span> <span class="token keyword">null</span> <span class="token operator">||</span> line2 <span class="token operator">!=</span> <span class="token keyword">null</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
         <span class="token keyword">if</span><span class="token punctuation">(</span>line1 <span class="token operator">==</span> <span class="token keyword">null</span> <span class="token operator">||</span> line2 <span class="token operator">==</span> <span class="token keyword">null</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
            areEqual <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span> 
            <span class="token keyword">break</span><span class="token punctuation">;</span>
         <span class="token punctuation">}</span> <span class="token keyword">else</span> <span class="token keyword">if</span><span class="token punctuation">(</span><span class="token operator">!</span> line1<span class="token punctuation">.</span><span class="token function">equalsIgnoreCase</span><span class="token punctuation">(</span>line2<span class="token punctuation">)</span><span class="token punctuation">) </span><span class="token punctuation">{</span>
            areEqual <span class="token operator">=</span> <span class="token boolean">false</span><span class="token punctuation">;</span> 
            <span class="token keyword">break</span><span class="token punctuation">;</span>
         <span class="token punctuation">}</span>
         line1 <span class="token operator">=</span> reader1<span class="token punctuation">.</span><span class="token function">readLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>  
         line2 <span class="token operator">=</span> reader2<span class="token punctuation">.</span><span class="token function">readLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
         lineNum<span class="token operator">++</span><span class="token punctuation">;</span>
      <span class="token punctuation">}</span>
      <span class="token keyword">if</span><span class="token punctuation">(</span>areEqual<span class="token punctuation">)</span><span class="token punctuation">{</span>
         <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Both the files have same content"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
      <span class="token punctuation">}<font color="#000000"> </font></span><span class="token keyword">else </span><span class="token punctuation">{</span>
         <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Both the files have different content"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
         <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"In both files, there is a difference at line number: "</span><span class="token operator">+</span>lineNum<span class="token punctuation">)</span><span class="token punctuation">;</span> 
         <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"One file has "</span><span class="token operator">+</span>line1<span class="token operator">+</span><span class="token string">" and another file has "</span><span class="token operator">+</span>line2<span class="token operator">+</span><span class="token string">" at line "</span><span class="token operator">+</span>lineNum<span class="token punctuation">)</span><span class="token punctuation">;</span>
      <span class="token punctuation">}</span>
      reader1<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
      reader2<span class="token punctuation">.</span><span class="token function">close</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
   <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

输出

Both the files have different content
In both files, there is a difference at line number: 2
One file has Java Language. and another file has Python Language. at line 2

注意 - 这里的输入场景类似于上面解释的实例2。

方法 2：使用内存映射文件

示例

在这种方法中，我们将利用内存映射文件的概念，这是一个将磁盘文件的字节映射到系统内存地址的内核对象，通过操作内存映射文件的内容，我们可以知道内容是相同还是不同。

<span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token class-name">File</span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>nio<span class="token punctuation">.</span>file<span class="token punctuation">.</span></span><span class="token class-name">Path</span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>nio<span class="token punctuation">.</span>file<span class="token punctuation">.</span></span><span class="token class-name">Paths</span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token class-name">IOException</span><span class="token punctuation">;</span>  
<span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>io<span class="token punctuation">.</span></span><span class="token class-name">RandomAccessFile</span><span class="token punctuation">;</span> 
<span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>nio<span class="token punctuation">.</span></span><span class="token class-name">MappedByteBuffer</span><span class="token punctuation">;</span>
<span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>nio<span class="token punctuation">.</span>channels<span class="token punctuation">.</span></span><span class="token class-name">FileChannel</span><span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Main</span> <span class="token punctuation">{</span>  
   <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token class-name">Path</span> path1 <span class="token operator">=</span> <span class="token class-name">Paths</span><span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token string">"E://file1.txt"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
      <span class="token class-name">Path</span> path2 <span class="token operator">=</span> <span class="token class-name">Paths</span><span class="token punctuation">.</span><span class="token function">get</span><span class="token punctuation">(</span><span class="token string">"E://file2.txt"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
      <span class="token function">compare</span><span class="token punctuation">(</span>path1<span class="token punctuation">,</span>path2<span class="token punctuation">)</span><span class="token punctuation">;</span>
   <span class="token punctuation">}</span>
   <span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">compare</span><span class="token punctuation">(</span><span class="token class-name">Path</span> path1<span class="token punctuation">,</span> <span class="token class-name">Path</span> path2<span class="token punctuation">)</span> <span class="token punctuation">{</span>
      <span class="token keyword">try</span> <span class="token punctuation">{</span>
         <span class="token class-name">RandomAccessFile</span> randomAccessFile1 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">RandomAccessFile</span><span class="token punctuation">(</span>path1<span class="token punctuation">.</span><span class="token function">toFile</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token string">"r"</span><span class="token punctuation">)</span><span class="token punctuation">;</span> 
         <span class="token class-name">RandomAccessFile</span> randomAccessFile2 <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">RandomAccessFile</span><span class="token punctuation">(</span>path2<span class="token punctuation">.</span><span class="token function">toFile</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token string">"r"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
         <span class="token class-name">FileChannel</span> ch1 <span class="token operator">=</span> randomAccessFile1<span class="token punctuation">.</span><span class="token function">getChannel</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
         <span class="token class-name">FileChannel</span> ch2 <span class="token operator">=</span> randomAccessFile2<span class="token punctuation">.</span><span class="token function">getChannel</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
         <span class="token keyword">if</span> <span class="token punctuation">(</span>ch1<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">!=</span> ch2<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Both files have different content"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
         <span class="token punctuation">}</span>
         <span class="token keyword">long</span> size <span class="token operator">=</span> ch1<span class="token punctuation">.</span><span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
         <span class="token class-name">MappedByteBuffer</span> m1 <span class="token operator">=</span> ch1<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token class-name">FileChannel<span class="token punctuation">.</span>MapMode</span><span class="token punctuation">.</span>READ_ONLY<span class="token punctuation">,</span> <span class="token number">0L</span><span class="token punctuation">,</span> size<span class="token punctuation">)</span><span class="token punctuation">;</span>
         <span class="token class-name">MappedByteBuffer</span> m2 <span class="token operator">=</span> ch2<span class="token punctuation">.</span><span class="token function">map</span><span class="token punctuation">(</span><span class="token class-name">FileChannel<span class="token punctuation">.</span>MapMode</span><span class="token punctuation">.</span>READ_ONLY<span class="token punctuation">,</span> <span class="token number">0L</span><span class="token punctuation">,</span> size<span class="token punctuation">)</span><span class="token punctuation">;</span>
         <span class="token keyword">if</span> <span class="token punctuation">(</span>m1<span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span>m2<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
            <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Both files have same content"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
         <span class="token punctuation">}</span>
      <span class="token punctuation">}</span>
      <span class="token keyword">catch</span><span class="token punctuation">(</span><span class="token class-name">Exception</span> e<span class="token punctuation">)</span><span class="token punctuation">{</span>
         <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>e<span class="token punctuation">)</span><span class="token punctuation">;</span>
      <span class="token punctuation">}</span>
   <span class="token punctuation">}</span>
<span class="token punctuation">}</span>

输出

Both files have same content

注意 - 这里我们考虑过的两个文件，它们具有相同的内容。

在本文中，我们探讨了如何在 Java 中逐行比较两个不同文本文件的内容。

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