FileUtils

1、方法writeByteArrayToFile(File file, byte[] data)：

	public static void writeByteArrayToFile(File file, byte[] data) throws IOException {
        OutputStream out = null;
        try {
            out = openOutputStream(file);
            out.write(data);
        } finally {
            IOUtils.closeQuietly(out);
        }
    }
	
	public static FileOutputStream openOutputStream(File file) throws IOException {
        if (file.exists()) {
            if (file.isDirectory()) {
                throw new IOException("File '" + file + "' exists but is a directory");
            }
            if (file.canWrite() == false) {
                throw new IOException("File '" + file + "' cannot be written to");
            }
        } else {
            File parent = file.getParentFile();
            if (parent != null && parent.exists() == false) {
                if (parent.mkdirs() == false) {
                    throw new IOException("File '" + file + "' could not be created");
                }
            }
        }
        return new FileOutputStream(file);
    }

 知识点：

获得一个文件名路径的上一层路径
File file = new File("D:\\almanac\\Ex1.java");
String parentPath = file.getParent();      // D:\almanac
File parentDir = file.getParentFile();     // D:\almanac

 

为什么new FileOutPutStream和new File创建不了文件？java.io.FileNotFoundException 系统找不到指定的路径

Java FileOutputStream Create File if not exists

结论：new FileOutputStream(file)创建文件时需要确保文件夹存在。（1级目录不需要）

 

2.方法readFileToString(File file)

public static String readFileToString(File file) throws IOException {
        return readFileToString(file, null);
    }

	public static String readFileToString(File file, String encoding) throws IOException {
        InputStream in = null;
        try {
            in = openInputStream(file);
            return IOUtils.toString(in, encoding);
        } finally {
            IOUtils.closeQuietly(in);
        }
    }

	public static FileInputStream openInputStream(File file) throws IOException {
        if (file.exists()) {
            if (file.isDirectory()) {
                throw new IOException("File '" + file + "' exists but is a directory");
            }
            if (file.canRead() == false) {
                throw new IOException("File '" + file + "' cannot be read");
            }
        } else {
            throw new FileNotFoundException("File '" + file + "' does not exist");
        }
        return new FileInputStream(file);
    }

 

//IOUtils:
	public static String toString(InputStream input, String encoding)
            throws IOException {
        StringWriter sw = new StringWriter();
        copy(input, sw, encoding);
        return sw.toString();   //通过StringWriter输出内容
    }
	
	public static void copy(InputStream input, Writer output, String encoding)
            throws IOException {
        if (encoding == null) {
            copy(input, output);
        } else {
            InputStreamReader in = new InputStreamReader(input, encoding);
            copy(in, output);
        }
    }

	public static void copy(InputStream input, Writer output)
            throws IOException {
        InputStreamReader in = new InputStreamReader(input);
        copy(in, output);
    }

	public static int copy(Reader input, Writer output) throws IOException {
        long count = copyLarge(input, output);
        if (count > Integer.MAX_VALUE) {
            return -1;
        }
        return (int) count;
    }
	
	public static long copyLarge(Reader input, Writer output) throws IOException {
        char[] buffer = new char[DEFAULT_BUFFER_SIZE];
        long count = 0;
        int n = 0;
        while (-1 != (n = input.read(buffer))) {
            output.write(buffer, 0, n);
            count += n;
        }
        return count;
    }

 总结：
    Writer.write(char[] cbuf, int off, int len) throws IOException
            //Writes a portion of an array of characters.

Parameters:
    cbuf - Array of characters
    off - Offset from which to start writing characters
    len - Number of characters to write

 

StringWriter sw = new StringWriter();
return sw.toString();   //通过StringWriter

 

3、方法writeStringToFile（File , Content , encoding）

public static void writeStringToFile(File file, String data, String encoding) throws IOException {
        OutputStream out = null;
        try {
            out = openOutputStream(file);
            IOUtils.write(data, out, encoding);
        } finally {
            IOUtils.closeQuietly(out);
        }
    }	
	
	public static FileOutputStream openOutputStream(File file) throws IOException {
        if (file.exists()) {
            if (file.isDirectory()) {
                throw new IOException("File '" + file + "' exists but is a directory");
            }
            if (file.canWrite() == false) {
                throw new IOException("File '" + file + "' cannot be written to");
            }
        } else {
            File parent = file.getParentFile();
            if (parent != null && parent.exists() == false) {
                if (parent.mkdirs() == false) {
                    throw new IOException("File '" + file + "' could not be created");
                }
            }
        }
        return new FileOutputStream(file);
    }
	
	//IOUtils
	public static void write(String data, OutputStream output, String encoding)
            throws IOException {
        if (data != null) {
            if (encoding == null) {
                write(data, output);
            } else {
                output.write(data.getBytes(encoding));
            }
        }
    }
	
	public static void write(String data, OutputStream output)
            throws IOException {
        if (data != null) {
            output.write(data.getBytes());
        }
    }

public static void write(StringBuffer data, Writer output)
            throws IOException {
        if (data != null) {
            output.write(data.toString());
        }
    }


    public static void write(StringBuffer data, OutputStream output)
            throws IOException {
        if (data != null) {
            output.write(data.toString().getBytes());
        }
    }

 。。