文件复制Util写法，可以适用于多种条件

代码写法：

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.Reader;
import java.io.StringWriter;
import java.io.Writer;

/**
 * 用于文件和流复制的简单实用方法。所有复制方法使用4096字节的块大小，并在完成后关闭所有受影响的流。
 */
public abstract class FileCopyUtils {

    public static final int BUFFER_SIZE = 4096;
    /**
     * 将给定输入文件的内容复制到给定的输出文件。
     * @param    要复制的文件
     * @param     将文件复制到
     * @return     复制的字节数
     * @throws     I / O错误时发生IOException
     */
    public static int copy(File in, File out) throws IOException {
        return copy(new BufferedInputStream(new FileInputStream(in)),
            new BufferedOutputStream(new FileOutputStream(out)));
    }

    /**
     * 将给定字节数组的内容复制到给定的输出文件。
     * @param     要从中复制的字节数组
     * @param    将文件复制到
     * @throws     I / O错误时发生IOException
     */
    public static void copy(byte[] in, File out) throws IOException {
        ByteArrayInputStream inStream = new ByteArrayInputStream(in);
        OutputStream outStream = new BufferedOutputStream(new FileOutputStream(out));
        copy(inStream, outStream);
    }

    /**
     * 将给定输入文件的内容复制到新的字节数组中。
     * @param     要复制的文件
     * @return     已复制到的新字节数组
     * @throws     I / O错误时发生IOException
     */
    public static byte[] copyToByteArray(File in) throws IOException {
        return copyToByteArray(new BufferedInputStream(new FileInputStream(in)));
    }
    /**
     * 将给定InputStream的内容复制到给定的OutputStream。完成后关闭两个流。
     * @param     复制到
     * @return     复制的字节数
     * @throws     I / O错误时发生IOException
     */
    public static int copy(InputStream in, OutputStream out) throws IOException {
        try {
            int byteCount = 0;
            byte[] buffer = new byte[BUFFER_SIZE];
            int bytesRead = -1;
            while ((bytesRead = in.read(buffer)) != -1) {
                out.write(buffer, 0, bytesRead);
                byteCount += bytesRead;
            }
            out.flush();
            return byteCount;
        }
        finally {
            try {
                in.close();
            }
            catch (IOException ex) {
            }
            try {
                out.close();
            }
            catch (IOException ex) {
            }
        }
    }

    /**
     * 将给定字节数组的内容复制到给定的OutputStream。完成后关闭流。
     * @param     要复制的字节数组
     * @param     输出要复制到的输出流
     * @throws     I / O错误时发生IOException
     */
    public static void copy(byte[] in, OutputStream out) throws IOException {
        try {
            out.write(in);
        }
        finally {
            try {
                out.close();
            }
            catch (IOException ex) {
            }
        }
    }

    /**
     * 将给定输入流的内容复制到新的字节数组中，完成后关闭流。
     * @return     已复制到的新字节数组
     * @throws     I / O错误时发生IOException
     */
    public static byte[] copyToByteArray(InputStream in) throws IOException {
        ByteArrayOutputStream out = new ByteArrayOutputStream(BUFFER_SIZE);
        copy(in, out);
        return out.toByteArray();
    }
    
    /*java.io.reader/java.io.writer的复制方法*/

    /**
     * 将给定读者的内容复制到给定的作者,完成后都关闭。
     */
    public static int copy(Reader in, Writer out) throws IOException {
        try {
            int byteCount = 0;
            char[] buffer = new char[BUFFER_SIZE];
            int bytesRead = -1;
            while ((bytesRead = in.read(buffer)) != -1) {
                out.write(buffer, 0, bytesRead);
                byteCount += bytesRead;
            }
            out.flush();
            return byteCount;
        }
        finally {
            try {
                in.close();
            }
            catch (IOException ex) {
            }
            try {
                out.close();
            }
            catch (IOException ex) {
            }
        }
    }

    /**
     * 将给定String的内容复制到给定的输出Writer。完成后关闭写入。
     */
    public static void copy(String in, Writer out) throws IOException {
        try {
            out.write(in);
        }
        finally {
            try {
                out.close();
            }
            catch (IOException ex) {
            }
        }
    }

    /**
     * 将给定Reader的内容复制到String中。完成后关闭读取。
     */
    public static String copyToString(Reader in) throws IOException {
        StringWriter out = new StringWriter();
        copy(in, out);
        return out.toString();
    }

}