io, nio常用代码收集-优快云博客

本文链接：https://blog.youkuaiyun.com/iteye_20037/article/details/82438880

本文介绍了Java中文件输入输出的基本操作方法，包括使用不同类型的流进行文件拷贝、读取和写入文本等，并提供了普通IO和NIO两种方式的具体实现。

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关闭流：


public static void closeSilently(Closeable closeable) {
    if (closeable != null) {
        try {
            closeable.close();
        } catch (IOException ex) {
        }
    }
}

普通io方式的拷贝:


/***
 * <p> 使用字节流进行拷贝. 拷贝完成后不会关闭流, 流的位置将保持在最后一次读取和写入的位置. </p>
 */
public static void copy(InputStream src, OutputStream dst, int bufferSize) throws IOException {
    BufferedOutputStream bos = new BufferedOutputStream(dst);
    byte[] buffer = new byte[bufferSize];
    int len;
    while ((len = src.read(buffer)) != -1) {
        bos.write(buffer, 0, len);
    }
    bos.flush();
}

/***
 * <p> 使用字符流进行拷贝. 拷贝完成后不会关闭流, 流的位置将保持在最后一次读取和写入的位置. </p>
 */
public static void copy(Reader src, Writer dst, int bufferSize) throws IOException {
    BufferedWriter bw = new BufferedWriter(dst);
    char[] buffer = new char[bufferSize];
    int len;
    while ((len = src.read(buffer)) != -1) {
        bw.write(buffer, 0, len);
    }
    bw.flush();
}

/***
 * <p> 使用随机访问文件进行拷贝. 拷贝完成后不会关闭文件, 位置将保持在最后一次读取和写入的位置. </p>
 */
public static void copy(RandomAccessFile src, RandomAccessFile dst, int bufferSize) throws IOException {
    byte[] buffer = new byte[bufferSize];
    int len;
    while ((len = src.read(buffer)) != -1) {
        dst.write(buffer, 0, len);
    }
}

nio方式的拷贝：


/***
 * <p> 使用FileChannel的transferFrom进行拷贝. transferFrom最大支持的文件在2GB左右, 不同的jvm可能会有不同的限制. </p>
 */
public static void copy(String srcFile, String dstFile) throws IOException {
    FileChannel srcChannel = null;
    FileChannel dstChannel = null;
    try {
        srcChannel = new FileInputStream(srcFile).getChannel();
        dstChannel = new RandomAccessFile(dstFile, "rw").getChannel();
        dstChannel.transferFrom(srcChannel, 0, srcChannel.size());
        // 或者
        // srcChannel.transferTo(0, dstChannel.size(), dstChannel);
    } finally {
        closeSilently(srcChannel);
        closeSilently(dstChannel);
    }
}

/***
 * <p> 使用Channel进行拷贝. 拷贝完成后不会关Channel, Channel将位置保持在最后一次读取和写入的位置.</p>
 */
public static void copy(ReadableByteChannel src, WritableByteChannel dst, int bufferSize) throws IOException {
    ByteBuffer buffer = ByteBuffer.allocate(bufferSize);
    while (src.read(buffer) != -1) {
        buffer.flip();
        dst.write(buffer);
        buffer.clear();
    }
}

普通io方式读取文本：


/***
 * <p> 从指定的流读取文本. 读取结束后流不会关闭. </p>
 * @param is 要读取文本的流
 * @param enc 流中文本所使用的编码
 * @return
 * @throws IOException
 */
public static String readString(InputStream is, String enc) throws IOException {
    try {
        return readString(new InputStreamReader(is, enc));
    } catch (UnsupportedEncodingException ex) {
        throw new IllegalArgumentException(ex);
    }
}

private static String readString(Reader r) throws IOException {
    BufferedReader reader = new BufferedReader(r);
    StringBuilder buffer = new StringBuilder();
    String line;
    while ((line = reader.readLine()) != null) {
        buffer.append(line);
    }
    return buffer.toString();
}

/***
 * <p> 从指定的文件读取文本. </p>
 * @param filepath 要读取文本的文件
 * @return
 * @throws IOException
 */
public static String readString(String filepath) throws IOException {
    // 不像InputStreamReader, FileReader可以自动识别文件的编码
    FileReader reader = null;
    try {
        reader = new FileReader(filepath);
        return readString(reader);
    } finally {
        closeSilently(reader);
    }
}

public static String scanString(String filepath) throws IOException {
    Scanner sc = null;
    try {
        File file = new File(filepath);
        sc = new Scanner(file);
        StringBuilder buffer = new StringBuilder((int) (file.length()/3));
        while (sc.hasNextLine()) {
            buffer.append(sc.nextLine());
        }
        return buffer.toString();
    } finally {
        if (sc != null) {
            sc.close();                
        }
    }
}

nio读取文本：


/***
 * <p> 以nio的方式从指定Chanle读取文本. 读取完成后不会关Channel, Channel将位置保持在最后一次读取的位置. </p>
 */
public static void readString(ReadableByteChannel src, int bufferSize, String enc) throws IOException  {
    try {
        ByteBuffer buffer = ByteBuffer.allocate(bufferSize);
        StringBuilder str = new StringBuilder();
        Charset cs = Charset.forName(enc);
        while (src.read(buffer) != -1) {
            buffer.flip();
            CharBuffer cbuffer = cs.decode(buffer);
            str.append(cbuffer.toString());
            buffer.clear();
            // 也可以使用
            /*
            int length = buffer.remaining();
            if (bytes == null || length > bytes.length) {
                bytes = new byte[length];
            }
            buffer.get(tmp, 0, length);
            String text = new String(tmp, enc);
            str.append(cbuffer.toString());
             */
        }
    } catch (UnsupportedEncodingException ex) {
        throw new IllegalArgumentException(ex);
    }
}

普通io方式写出文本：


/***
 * <p> 将文本写入到指定的输出流中. 写入完毕后流不会关闭. </p>
 * @param text
 * @param os
 * @param enc
 * @throws IOException
 */
public static void writeString(String text, OutputStream os, String enc) throws IOException {
    try {
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(os, enc));
        bw.write(text);
        bw.flush();
    } catch (UnsupportedEncodingException ex) {
        throw new IllegalArgumentException(ex);
    }
}

public static void writeString(String text, Writer writer) throws IOException {
    BufferedWriter bw = new BufferedWriter(writer);
    bw.write(text);
}

/***
 * <p> 将文本写入到指定的文件中. </p>
 * @param text
 * @param filepath
 * @throws IOException
 */
public static void writeString(String text, String filepath) throws IOException {
    FileWriter fw = null;
    try {
        fw = new FileWriter(filepath);
        writeString(text, fw);
    } finally {
        closeSilently(fw);
    }
}

public static void printString(String text, String filepath) throws IOException {
    PrintWriter pw = null;
    try {
        pw = new PrintWriter(new File(filepath));
        pw.print(text);
    } finally {
        closeSilently(pw);
    }
}

nio写出文本：


/***
 * <p> 以nio的方式将文本写入Chanle. 写入完成后不会关Channel, Channel将位置保持在最后一次写入的位置. </p>
 * @param dst 要写入的channel
 * @param text 要写出的文本
 * @param enc 文本转换为字节时的编码
 * @param bufferSize ByteBuffer的大小
 */
public static void writeString(WritableByteChannel dst, String text, String enc, int bufferSize) throws IOException {
    byte[] textBytes = text.getBytes(enc);
    writeString(dst, textBytes, bufferSize);
}

/***
 * <p> 以nio的方式将文本写入Chanle. 写入完成后不会关Channel, Channel将位置保持在最后一次写入的位置. </p>
 * @param dst 要写入的channel
 * @param textBytes 文本经过编码后的字节
 * @param bufferSize ByteBuffer的大小
 */
public static void writeString(WritableByteChannel dst, byte[] textBytes, int bufferSize) throws IOException {
    int i = 0;
    int strBytesLength = textBytes.length;

    ByteBuffer buffer = ByteBuffer.allocate(bufferSize);
    for (; i < strBytesLength && i + bufferSize < strBytesLength; i += bufferSize) {
        buffer.put(textBytes, i, bufferSize);
        buffer.flip();
        dst.write(buffer);
        buffer.clear();
    }
    int remind = textBytes.length - i;
    buffer.put(textBytes, i, remind);
    buffer.flip();
    dst.write(buffer);
}