Java之IO流进阶篇：内存流，打印流，对象流

发布时间：2020-12-14 06:33:45 所属栏目：Java 来源：网络整理

导读：? 输入输出流子类众多，详情见下图：用来操作内存 ByteArrayInputStream ? ? 内存到程序不需要关闭不使用内存资源，内存不够建议不用 ByteArrayOutputStream 程序到内存不需要关闭不使用内存资源，内存不够建议不用内存输入流和内存输出流：首先创建

输入输出流子类众多，详情见下图：

　　用来操作内存

　　ByteArrayInputStream　? ?　内存到程序　　不需要关闭　　不使用内存资源，内存不够建议不用

　　ByteArrayOutputStream　　程序到内存　　不需要关闭　　不使用内存资源，内存不够建议不用

内存输入流和内存输出流：

首先创建字节数组，一般引用数据类型存放在内存中。显然此时，可以创建字节数组输入流，读入程序当中。

import java.io.ByteArrayInputStream;
import java.io.IOException;

public class ByteArrayInputStreamDemo {

</span><span style="color: #0000ff"&gt;public</span> <span style="color: #0000ff"&gt;static</span> <span style="color: #0000ff"&gt;void</span> main(String[] args) <span style="color: #0000ff"&gt;throws</span><span style="color: #000000"&gt; IOException {
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt; TODO Auto-generated method stub
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;1.创建字节数组（要读取的数据）</span>
    <span style="color: #0000ff"&gt;byte</span>[] data= {10,15,50,33,12,22<span style="color: #000000"&gt;};
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;2.创建流</span>
    ByteArrayInputStream bais=<span style="color: #0000ff"&gt;new</span><span style="color: #000000"&gt; ByteArrayInputStream(data);
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;3.读取

// int d;
// while((d=bais.read())!=-1) {
// System.out.println(d);
// }
// bais.close();//实际操作中无需关闭流
byte[] buf=new byte[1024];
int len;
while((len=bais.read(buf))!=-1) {
for (int i = 0; i < len; i++) {
System.out.println(buf[i]);
}
}
}
}

<span style="color: #0000ff">import<span style="color: #000000"> java.io.ByteArrayOutputStream;
<span style="color: #0000ff">public <span style="color: #0000ff">class<span style="color: #000000"> ByteArrayOutputStreamDemo {
</span><span style="color: #0000ff"&gt;public</span> <span style="color: #0000ff"&gt;static</span> <span style="color: #0000ff"&gt;void</span><span style="color: #000000"&gt; main(String[] args) {
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt; TODO Auto-generated method stub
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;1.创建字节数组输出流对象</span>
    ByteArrayOutputStream baos=<span style="color: #0000ff"&gt;new</span><span style="color: #000000"&gt; ByteArrayOutputStream();
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;2.写入数据</span>
    baos.write(12<span style="color: #000000"&gt;);
    baos.write(</span>20<span style="color: #000000"&gt;);
    baos.write(</span>18<span style="color: #000000"&gt;);
    baos.write(</span>32<span style="color: #000000"&gt;);
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;3.获取输出流中的字节数据</span>
    <span style="color: #0000ff"&gt;byte</span>[] data=<span style="color: #000000"&gt;baos.toByteArray();
    </span><span style="color: #0000ff"&gt;for</span> (<span style="color: #0000ff"&gt;byte</span><span style="color: #000000"&gt; b : data) {
        System.out.println(b);
    }
}
}

使用内存流读取图片：

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class ReadImg {

</span><span style="color: #0000ff"&gt;public</span> <span style="color: #0000ff"&gt;static</span> <span style="color: #0000ff"&gt;void</span> main(String[] args) <span style="color: #0000ff"&gt;throws</span><span style="color: #000000"&gt; IOException {
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt; TODO Auto-generated method stub
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;1.创建文件字节输入流</span>
    FileInputStream fis=<span style="color: #0000ff"&gt;new</span> FileInputStream("E:xx.png"<span style="color: #000000"&gt;);
    ByteArrayOutputStream baos</span>=<span style="color: #0000ff"&gt;new</span><span style="color: #000000"&gt; ByteArrayOutputStream();
    </span><span style="color: #0000ff"&gt;byte</span>[] buf=<span style="color: #0000ff"&gt;new</span> <span style="color: #0000ff"&gt;byte</span>[1024<span style="color: #000000"&gt;];
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;2.读取数据</span>
    <span style="color: #0000ff"&gt;int</span><span style="color: #000000"&gt; len;
    </span><span style="color: #0000ff"&gt;while</span>((len=fis.read(buf))!=-1<span style="color: #000000"&gt;) {
        baos.write(buf,</span>0<span style="color: #000000"&gt;,len);
    }
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;3.获取图片数据</span>
    <span style="color: #0000ff"&gt;byte</span>[] imgbyte=<span style="color: #000000"&gt;baos.toByteArray();
    System.out.println(imgbyte.length);
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;4.创建文件输出流</span>
    FileOutputStream fos=<span style="color: #0000ff"&gt;new</span> FileOutputStream("E:xx1.png"<span style="color: #000000"&gt;);
    ByteArrayInputStream bais</span>=<span style="color: #0000ff"&gt;new</span><span style="color: #000000"&gt; ByteArrayInputStream(imgbyte);
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;5.读取数组</span>
    <span style="color: #0000ff"&gt;byte</span>[] buf1=<span style="color: #0000ff"&gt;new</span> <span style="color: #0000ff"&gt;byte</span>[1024<span style="color: #000000"&gt;];
    </span><span style="color: #0000ff"&gt;int</span><span style="color: #000000"&gt; len1;
    </span><span style="color: #0000ff"&gt;while</span>((len1=bais.read(buf1))!=-1<span style="color: #000000"&gt;) {
        fos.write(buf1,len1);
    }
    fis.close();
    fos.close();
    bais.close();
    baos.close();
}

}

2.打印流

import java.io.BufferedOutputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintStream;

public class PrintStreamDemo {
//打印流（字节）
public static void main(String[] args) throws IOException {
// TODO Auto-generated method stub
//PrintStream ps=new PrintStream("E:aaa.txt");
BufferedOutputStream bos=new BufferedOutputStream(new FileOutputStream("E:xx.txt"));
PrintStream ps=new PrintStream(bos,true);
ps.print("123456");
ps.print(true);
ps.println("abcdef");
ps.printf("%d",200);
ps.printf("%.2f",3.1415926);
ps.printf("%s","我爱生活");
ps.printf("%x",256);

}

import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;

public class PrintWriterDemo {

</span><span style="color: #0000ff"&gt;public</span> <span style="color: #0000ff"&gt;static</span> <span style="color: #0000ff"&gt;void</span> main(String[] args) <span style="color: #0000ff"&gt;throws</span><span style="color: #000000"&gt; IOException {
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt; TODO Auto-generated method stub</span>
    PrintWriter pw=<span style="color: #0000ff"&gt;new</span> PrintWriter(<span style="color: #0000ff"&gt;new</span> FileOutputStream("E:bbb.txt"<span style="color: #000000"&gt;));
    pw.println(</span>"123"<span style="color: #000000"&gt;);
    pw.close();
}

}

3.对象序列化与反序列化（对象流）

import java.io.Serializable;

public class Student implements Serializable {
private static final long serialVersionUID=123L;//序列化与反序列化的唯一标记
private int StuNo;//序列化和访问权限没有关系
 String name;
//transient int age;//transient 瞬时的，不能序列化瞬时的属性
//static String address="北京";//静态变量不能被序列化
public Student() {
super();
// TODO Auto-generated constructor stub
 }

    </span><span style="color: #0000ff"&gt;public</span> Student(<span style="color: #0000ff"&gt;int</span><span style="color: #000000"&gt; stuNo,String name) {
        </span><span style="color: #0000ff"&gt;super</span><span style="color: #000000"&gt;();
        StuNo </span>=<span style="color: #000000"&gt; stuNo;
        </span><span style="color: #0000ff"&gt;this</span>.name =<span style="color: #000000"&gt; name;
    }

    </span><span style="color: #0000ff"&gt;public</span> <span style="color: #0000ff"&gt;int</span><span style="color: #000000"&gt; getStuNo() {
        </span><span style="color: #0000ff"&gt;return</span><span style="color: #000000"&gt; StuNo;
    }
    </span><span style="color: #0000ff"&gt;public</span> <span style="color: #0000ff"&gt;void</span> setStuNo(<span style="color: #0000ff"&gt;int</span><span style="color: #000000"&gt; stuNo) {
        StuNo </span>=<span style="color: #000000"&gt; stuNo;
    }
    </span><span style="color: #0000ff"&gt;public</span><span style="color: #000000"&gt; String getName() {
        </span><span style="color: #0000ff"&gt;return</span><span style="color: #000000"&gt; name;
    }
    </span><span style="color: #0000ff"&gt;public</span> <span style="color: #0000ff"&gt;void</span><span style="color: #000000"&gt; setName(String name) {
        </span><span style="color: #0000ff"&gt;this</span>.name =<span style="color: #000000"&gt; name;
    }

}

使用对象类序列化和反序列化学生类：

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class SerializeDemo {

</span><span style="color: #0000ff"&gt;public</span> <span style="color: #0000ff"&gt;static</span> <span style="color: #0000ff"&gt;void</span> main(String[] args) <span style="color: #0000ff"&gt;throws</span><span style="color: #000000"&gt; IOException,ClassNotFoundException {
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;序列化过程：
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;1.创建序列化对象</span>
    Student stu=<span style="color: #0000ff"&gt;new</span> Student(1101,"小明"<span style="color: #000000"&gt;);
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;2.创建文件输出流</span>
    FileOutputStream fos=<span style="color: #0000ff"&gt;new</span> FileOutputStream("E:receive.bin"<span style="color: #000000"&gt;);
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;3.创建对象流接入输出流</span>
    ObjectOutputStream oos=<span style="color: #0000ff"&gt;new</span><span style="color: #000000"&gt; ObjectOutputStream(fos);
    </span><span style="color: #008000"&gt;//</span><span style="color: #008000"&gt;4.对象流输出序列化对象保存在文件中</span>

oos.writeObject(stu);
oos.close();
//反序列化过程：
//1.创建对象流
FileInputStream fis=new FileInputStream("E:receive.bin") ;
ObjectInputStream ois=new ObjectInputStream(fis);
//2.反序列化
Student stu1=(Student)ois.readObject();
ois.close();
System.out.println("学号："+stu1.getStuNo());
System.out.println("姓名："+stu1.getName());
}
}

控制台输出信息（表明反序列化成功）：

（编辑：李大同）

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