Java 基础: IO流 -- 字节流和字符流的区别和使用,分别实现文本的复制(详细)

于 2022-03-01 17:11:15 发布
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分类专栏： IO流 文章标签： java 开发语言 后端
原文链接：https://blog.youkuaiyun.com/qq_43619271/article/details/106301667
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本文详细介绍了Java中的IO流，包括字节流和字符流的基本概念、使用方法以及如何实现文件的读取、写入和复制。在文件复制过程中，强调了分块流动的重要性，以避免文件内容不一致的问题。同时，通过实例展示了字符流如何实现文件复制并替换占位符内容。

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前置知识: File 类的基本使用与了解。

流:

在介绍 IO 流之前先来说下什么是流: 流是一种 FIFO 的数据结构(类似于队列,先进先出)。简单来说,就像水流一样。

输入流和输出流:

输入流和输出流是相对于 内存 这个参照物来说的。
在这里插入图片描述

流的划分:

在这里插入图片描述
上图中很多类都是抽象类,所以都需要通过其子类进行实现。
(父类引用指向子类对象 – 多态)
注意:
1、字节流:字节流就是将内容转为了字节形式进行传输, 1 字节 有 8 个二进制位组成,在底层,文件都是有二进制组成的,所以二进制可以传输任何类型的数据,进而 字节流也可以传输任何类型的数据。
2、字节流是 8 位通用字节流(可以处理任意类型,处理文本以外的其他文件)
3、字符流是 16 位 unicode 字符流(只用于处理字符,处理文本文件)
4、字符流:一般只用来处理字符,当我们传输图片的时候,转码的时候容易出现乱码,字节流也可以处理字符相关的文本,但是效率没有字符流更好。

输入流实现文本的读取:

在流到内存的时候因为我们不知道文件的具体大小,也就是字节数组的大小开多少比较合适
我们是不知道的,所以需要通过 in.available() 方法得到文件的大小,进而实现流动。

package io;

import java.io.*;

public class Demo03 { 

<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>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> IOException <span class="token punctuation">{<!-- --></span>
    <span class="token comment">// 提高作用域,便于关闭</span>
    InputStream in <span class="token operator">=</span> null<span class="token punctuation">;</span>
    <span class="token keyword">try</span><span class="token punctuation">{<!-- --></span>
        <span class="token comment">// InputStream 是一个抽象类,需要通过子类进行实现</span>
        in <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">FileInputStream</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">File</span><span class="token punctuation">(</span><span class="token string">"hello.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// 得到文件的总大小</span>
        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>in<span class="token punctuation">.</span><span class="token function">available</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token comment">// 先将文件放到缓冲区里面,这里的缓冲区是一个 字节数组</span>
        <span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> buf <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">byte</span><span class="token punctuation">[</span>in<span class="token punctuation">.</span><span class="token function">available</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">]</span><span class="token punctuation">;</span>

        <span class="token comment">// 流到内存中</span>
        in<span class="token punctuation">.</span><span class="token function">read</span><span class="token punctuation">(</span>buf<span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// 输出一下</span>
        System<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 keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span>buf<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">FileNotFoundException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
        e<span class="token punctuation">.</span><span class="token function">printStackTrace</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">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
        e<span class="token punctuation">.</span><span class="token function">printStackTrace</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">finally</span> <span class="token punctuation">{<!-- --></span>
        <span class="token comment">// 防止出现空指针</span>
        <span class="token keyword">if</span><span class="token punctuation">(</span>in <span class="token operator">!=</span> null<span class="token punctuation">)</span> in<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>

}

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hello.txt 文本中的内容:
在这里插入图片描述
输出结果;
在这里插入图片描述

输出流实现将内容输出到文件中:

package io;

import java.io.*;

public class Demo04 { 

<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>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token keyword">throws</span> IOException <span class="token punctuation">{<!-- --></span>
    OutputStream out <span class="token operator">=</span> null<span class="token punctuation">;</span>
    <span class="token keyword">try</span> <span class="token punctuation">{<!-- --></span>
        <span class="token comment">// 与 输入流类似</span>
        out <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">FileOutputStream</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">File</span><span class="token punctuation">(</span><span class="token string">"d.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token comment">// 通过子节的方式将 hello123 读取到 d.txt 文件中</span>
        out<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span><span class="token string">"hello123"</span><span class="token punctuation">.</span><span class="token function">getBytes</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> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">FileNotFoundException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
        e<span class="token punctuation">.</span><span class="token function">printStackTrace</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">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
        e<span class="token punctuation">.</span><span class="token function">printStackTrace</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">finally</span> <span class="token punctuation">{<!-- --></span>
       <span class="token keyword">if</span><span class="token punctuation">(</span>out <span class="token operator">!=</span> null<span class="token punctuation">)</span> out<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>

}

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d.txt
在这里插入图片描述

字节流实现文件的复制:

在实现文件的复制时,需要注意以下几点:
1、由于文件可能很大,可能有几个G,但是我们不可能一次开辟那么大的空间,所以可以分块进行流动,每次开辟一定的空间。
2、分块流动时可能会有多出来的一部分: 比如 135 byte,我们规定每次最多只能传输 10 byte，但是 最后会 只剩下 5 byte 还没有传输,这个时候缓冲区里面存储的还是上一次的 10byte,而新来的 5byte 只会替换前 5 个:如下图:
原文件:
在这里插入图片描述
复制后的文件:
在这里插入图片描述
可以清晰的看到,复制后的文件与原文件中的内容出现不一致,这个问题该怎么处理呢？
详见代码:



 
 

 
 
  • 1

3、一定要记得关闭 输入流和输出流,否则会出现文件内容读不进去的尴尬！

package io;

import java.io.*;

public class Demo05 { 

<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>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>

    InputStream in <span class="token operator">=</span> null<span class="token punctuation">;</span>
    OutputStream out <span class="token operator">=</span> null<span class="token punctuation">;</span>

    <span class="token keyword">try</span><span class="token punctuation">{<!-- --></span>
        <span class="token comment">// 将原文件读到内存区</span>
        in <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">FileInputStream</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">File</span><span class="token punctuation">(</span><span class="token string">"a.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token comment">// 从 内存区 输出到 要复制的地方</span>
        out <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">FileOutputStream</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">File</span><span class="token punctuation">(</span><span class="token string">"b.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// 缓存区(每次都流动 10 byte)</span>
        <span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> buf <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">byte</span><span class="token punctuation">[</span><span class="token number">10</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
        <span class="token keyword">int</span> len <span class="token operator">=</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>
        <span class="token comment">// in.read(buf) 返回值是流动到 内存区的 长度</span>
        <span class="token keyword">while</span><span class="token punctuation">(</span><span class="token punctuation">(</span>len <span class="token operator">=</span> in<span class="token punctuation">.</span><span class="token function">read</span><span class="token punctuation">(</span>buf<span class="token punctuation">)</span> <span class="token punctuation">)</span><span class="token operator">!=</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
            <span class="token comment">// 每次都流动的是 实际 的长度(这样可以避免出现文件不一致的情况)</span>
            out<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span>buf<span class="token punctuation">,</span><span class="token number">0</span><span class="token punctuation">,</span>len<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">FileNotFoundException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
        e<span class="token punctuation">.</span><span class="token function">printStackTrace</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">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
        e<span class="token punctuation">.</span><span class="token function">printStackTrace</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">finally</span> <span class="token punctuation">{<!-- --></span>
        <span class="token keyword">try</span> <span class="token punctuation">{<!-- --></span>
            <span class="token comment">// 一定要记得关 流</span>
            <span class="token keyword">if</span><span class="token punctuation">(</span>out <span class="token operator">!=</span> null<span class="token punctuation">)</span> out<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 keyword">if</span><span class="token punctuation">(</span>in <span class="token operator">!=</span> null<span class="token punctuation">)</span> in<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 keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
            e<span class="token punctuation">.</span><span class="token function">printStackTrace</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>

<span class="token punctuation">}</span>

}

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字符流实现文件的复制:

实现功能:
在这里插入图片描述
将a.txt文件中的内容 复制到 b.txt 文件中,并且将占位符替换掉。

package io;

import java.io.*;

public class Demo06 { 

<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>String<span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
    Reader in <span class="token operator">=</span> null<span class="token punctuation">;</span>
    Writer out <span class="token operator">=</span> null<span class="token punctuation">;</span>
    <span class="token keyword">try</span> <span class="token punctuation">{<!-- --></span>

        <span class="token comment">// 字符输入流</span>
        in <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">FileReader</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">File</span><span class="token punctuation">(</span><span class="token string">"a.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token comment">// 字符输出流</span>
        out <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">FileWriter</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">File</span><span class="token punctuation">(</span><span class="token string">"b.txt"</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token comment">// 字节流是 字节数组作为缓冲区,字符流是 字符数组作为缓冲区</span>
        <span class="token keyword">char</span><span class="token punctuation">[</span><span class="token punctuation">]</span> buf <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">char</span><span class="token punctuation">[</span><span class="token number">4</span><span class="token punctuation">]</span><span class="token punctuation">;</span>
        <span class="token comment">// 拼接字符串,由于 Sting 每次拼接时都要在 常量池中开辟新的空间,效率较低,所以我们选择用 StringBuffer</span>
        StringBuffer sb <span class="token operator">=</span> <span class="token keyword">new</span>  <span class="token class-name">StringBuffer</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token keyword">int</span> len <span class="token operator">=</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">;</span>

        <span class="token keyword">while</span><span class="token punctuation">(</span><span class="token punctuation">(</span>len <span class="token operator">=</span> in<span class="token punctuation">.</span><span class="token function">read</span><span class="token punctuation">(</span>buf<span class="token punctuation">)</span><span class="token punctuation">)</span> <span class="token operator">!=</span> <span class="token operator">-</span><span class="token number">1</span><span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
            sb<span class="token punctuation">.</span><span class="token function">append</span><span class="token punctuation">(</span>buf<span class="token punctuation">,</span><span class="token number">0</span><span class="token punctuation">,</span>len<span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">}</span>

        System<span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>sb<span class="token punctuation">)</span><span class="token punctuation">;</span>

        <span class="token comment">// 转换为 String 类型,替换相应的内容</span>
        String content <span class="token operator">=</span> sb<span class="token punctuation">.</span><span class="token function">toString</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        content <span class="token operator">=</span> content<span class="token punctuation">.</span><span class="token function">replace</span><span class="token punctuation">(</span><span class="token string">"name"</span><span class="token punctuation">,</span><span class="token string">"潘小蓝"</span><span class="token punctuation">)</span>
                  <span class="token punctuation">.</span><span class="token function">replace</span><span class="token punctuation">(</span><span class="token string">"age"</span><span class="token punctuation">,</span><span class="token string">"22"</span><span class="token punctuation">)</span>
                  <span class="token punctuation">.</span><span class="token function">replace</span><span class="token punctuation">(</span><span class="token string">"address"</span><span class="token punctuation">,</span><span class="token string">"HN"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token comment">// 输出到 相应文件中</span>
        out<span class="token punctuation">.</span><span class="token function">write</span><span class="token punctuation">(</span>content<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">FileNotFoundException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
        e<span class="token punctuation">.</span><span class="token function">printStackTrace</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">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
        e<span class="token punctuation">.</span><span class="token function">printStackTrace</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">finally</span> <span class="token punctuation">{<!-- --></span>

        <span class="token keyword">try</span> <span class="token punctuation">{<!-- --></span>
           <span class="token keyword">if</span><span class="token punctuation">(</span>in <span class="token operator">!=</span> null<span class="token punctuation">)</span> in<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 keyword">if</span><span class="token punctuation">(</span>out <span class="token operator">!=</span> null<span class="token punctuation">)</span> out<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 keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">IOException</span> e<span class="token punctuation">)</span> <span class="token punctuation">{<!-- --></span>
            e<span class="token punctuation">.</span><span class="token function">printStackTrace</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>


<span class="token punctuation">}</span>

}

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效果图:
在这里插入图片描述

后记:

如果各位看官有疑问的或者有哪里解释的不清楚的，欢迎提出,在下会细心改正,大家共同进步,加油！！！

[转载自](https://blog.youkuaiyun.com/qq_43619271/article/details/106301667)
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