java读取文件内容再编辑

有时候，我们需要将读取文件的内容到一个byte[] 数组中，然后对这个数组进行一些修改，这时，我们可以借助于ByteArrayOutputStream 这个类来实现。
　　ByteArrayOutputStream，顾名思义，同样是一个OutputStream，那么，对于它的写入操作，和其他的 OutputStream应该是没有什么两样，写入代码可以说是随手拈来的，与其他输出流的不同之处在于，ByteArrayOutputStream写入到内存中，并提供一个 toByteArray() 方法返回我们所需要的byte[]。
　

//保存上传的附件信息
	String filename = files[0];
	String filepath = "upload/append/"+files[1];
						BufferedInputStream in = new BufferedInputStream(new FileInputStream(filepath));
						ByteArrayOutputStream out = new ByteArrayOutputStream(2048);
						System.out.println("available bytes"+in.available());
	byte[] temp = new byte[2048];
	int size =0;
	while((size = in.read(temp))!=-1){				   out.write(temp,0,size);
	}
	in.close();
	byte[] content = out.toByteArray();

	String stream = new BaseCode64().EncodeBase64(content);
	System.out.println("content" +content.length);
         effect += insertAttachmentInfo(conn,attNo,processId,filename,stream);

这里把读取的流以base64保存，使用了类BaseCode64()的方法EncodeBase64。
代码如下：

package com.ving.xzfw.util;

import java.io.ByteArrayOutputStream;

public class BaseCode64 {
	private String TableBase64;
	private String FError;
	
	public BaseCode64()
	{
		TableBase64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
		FError = new String();
		FError = "";
	}
	public String DecodeBase64(byte [] Value){
		
		ByteArrayOutputStream o = new ByteArrayOutputStream();
		byte d[] = new byte[4];
		try
		{
			int count = 0;
			byte x[] = Value;
			do
			{
				if(count >= x.length)
				{
					break;
				}
				for(int n = 0; n <= 3; n++)
				{
					if(count >= x.length)
					{
						d[n] = 64;
					} else
					{
						int y = TableBase64.indexOf(x[count]);
						if(y < 0)
						{
							y = 65;
						}
						d[n] = (byte)y;
					}
					count++;
				}
				
				o.write((byte)(((d[0] & 0x3f) << 2) + ((d[1] & 0x30) >> 4)));
				if(d[2] != 64)
				{
					o.write((byte)(((d[1] & 0xf) << 4) + ((d[2] & 0x3c) >> 2)));
					if(d[3] != 64)
					{
						o.write((byte)(((d[2] & 3) << 6) + (d[3] & 0x3f)));
					}
				}
			} while(true);
		}
		catch(StringIndexOutOfBoundsException e)
		{
			FError = String.valueOf(String.valueOf(FError)) + String.valueOf(String.valueOf(e.toString()));
			System.out.println(e.toString());
		}
		return o.toString();
		
	}
	
	public String EncodeBase64(byte [] Value){
		ByteArrayOutputStream o = new ByteArrayOutputStream();
		byte d[] = new byte[4];
		try
		{
			int count = 0;
			for(byte x[] = Value; count < x.length;)
			{
				byte c = x[count];
				count++;
				d[0] = (byte)((c & 0xfc) >> 2);
				d[1] = (byte)((c & 3) << 4);
				if(count < x.length)
				{
					c = x[count];
					count++;
					d[1] = (byte)(d[1] + (byte)((c & 0xf0) >> 4));
					d[2] = (byte)((c & 0xf) << 2);
					if(count < x.length)
					{
						c = x[count];
						count++;
						d[2] = (byte)(d[2] + ((c & 0xc0) >> 6));
						d[3] = (byte)(c & 0x3f);
					} else
					{
						d[3] = 64;
					}
				} else
				{
					d[2] = 64;
					d[3] = 64;
				}
				int n = 0;
				while(n <= 3) 
				{
					o.write(TableBase64.charAt(d[n]));
					n++;
				}
			}
			
		}
		catch(StringIndexOutOfBoundsException e)
		{
			FError = String.valueOf(String.valueOf(FError)) + String.valueOf(String.valueOf(e.toString()));
			System.out.println(e.toString());
		}
		return o.toString();
	}
}