Java中InputStream重复使用问题的几种解决方案_Java

前言

在java中，inputstream通常设计为"一次性"使用，读取后流会到达末尾，再次读取时会返回-1或抛出异常。以下是几种实现inputstream重复使用的方法：

1. 使用mark()和reset()方法（适用于支持标记的流）

java

import java.io.*;

public class inputstreamreuser {
    public static void main(string[] args) throws ioexception {
        string data = "hello world";
        inputstream inputstream = new bytearrayinputstream(data.getbytes());
        
        // 第一次读取前标记
        if (inputstream.marksupported()) {
            inputstream.mark(0); // 参数是readlimit，0表示不限制
        }
        
        // 第一次读取
        system.out.println("第一次读取:");
        readandprint(inputstream);
        
        // 重置流
        if (inputstream.marksupported()) {
            inputstream.reset();
        }
        
        // 第二次读取
        system.out.println("第二次读取:");
        readandprint(inputstream);
    }
    
    private static void readandprint(inputstream is) throws ioexception {
        int content;
        while ((content = is.read()) != -1) {
            system.out.print((char) content);
        }
        system.out.println();
    }
}

2. 将流内容缓存到字节数组（最可靠方法）

java

import java.io.*;

public class inputstreamcacher {
    public static void main(string[] args) throws ioexception {
        inputstream originalstream = new fileinputstream("example.txt");
        
        // 将流内容缓存到字节数组
        byte[] bytes = readallbytes(originalstream);
        originalstream.close();
        
        // 创建可重复使用的流
        inputstream reusablestream1 = new bytearrayinputstream(bytes);
        inputstream reusablestream2 = new bytearrayinputstream(bytes);
        
        // 使用流1
        system.out.println("第一次使用:");
        readandprint(reusablestream1);
        
        // 使用流2
        system.out.println("第二次使用:");
        readandprint(reusablestream2);
    }
    
    private static byte[] readallbytes(inputstream is) throws ioexception {
        bytearrayoutputstream buffer = new bytearrayoutputstream();
        byte[] data = new byte[1024];
        int nread;
        while ((nread = is.read(data, 0, data.length)) != -1) {
            buffer.write(data, 0, nread);
        }
        return buffer.tobytearray();
    }
    
    private static void readandprint(inputstream is) throws ioexception {
        int content;
        while ((content = is.read()) != -1) {
            system.out.print((char) content);
        }
        system.out.println();
    }
}

3. 使用apache commons io的ioutils（简化代码）

java

import org.apache.commons.io.ioutils;
import java.io.*;

public class commonsioexample {
    public static void main(string[] args) throws ioexception {
        inputstream originalstream = new fileinputstream("example.txt");
        
        // 将流转换为字节数组
        byte[] bytes = ioutils.tobytearray(originalstream);
        originalstream.close();
        
        // 创建可重复使用的流
        inputstream reusablestream1 = new bytearrayinputstream(bytes);
        inputstream reusablestream2 = new bytearrayinputstream(bytes);
        
        // 使用流
        system.out.println("第一次使用: " + ioutils.tostring(reusablestream1, "utf-8"));
        system.out.println("第二次使用: " + ioutils.tostring(reusablestream2, "utf-8"));
    }
}

4. 自定义可重置的inputstream包装器

java

import java.io.*;

public class resettableinputstream extends inputstream {
    private final inputstream original;
    private inputstream current;
    private byte[] buffer;
    private boolean buffered = false;
    
    public resettableinputstream(inputstream original) {
        this.original = original;
        this.current = original;
    }
    
    @override
    public int read() throws ioexception {
        return current.read();
    }
    
    public void resetstream() throws ioexception {
        if (!buffered) {
            // 第一次重置时缓存内容
            bytearrayoutputstream baos = new bytearrayoutputstream();
            byte[] data = new byte[1024];
            int nread;
            while ((nread = original.read(data, 0, data.length)) != -1) {
                baos.write(data, 0, nread);
            }
            buffer = baos.tobytearray();
            buffered = true;
        }
        current = new bytearrayinputstream(buffer);
    }
    
    @override
    public void close() throws ioexception {
        original.close();
        if (buffered && current != null) {
            current.close();
        }
    }
}

// 使用示例
public class main {
    public static void main(string[] args) throws ioexception {
        resettableinputstream ris = new resettableinputstream(new fileinputstream("example.txt"));
        
        // 第一次读取
        system.out.println("第一次读取:");
        readandprint(ris);
        
        // 重置
        ris.resetstream();
        
        // 第二次读取
        system.out.println("第二次读取:");
        readandprint(ris);
        
        ris.close();
    }
    
    private static void readandprint(inputstream is) throws ioexception {
        int content;
        while ((content = is.read()) != -1) {
            system.out.print((char) content);
        }
        system.out.println();
    }
}