聲明：本系列只供本人自學(xué)使用图云，勿噴。

實(shí)際開發(fā)中最常用的就是文件IO邻邮，通常情況下竣况，操作二進(jìn)制文件用字節(jié)流，文本文件用字符流筒严。

一丹泉、文件字節(jié)流

1.FileInputStream

• 構(gòu)造器

//實(shí)際調(diào)用FileInputStream(File file)
public FileInputStream(String name) throws FileNotFoundException
public FileInputStream(File file) throws FileNotFoundException{
    1.文件安全及權(quán)限檢查
    2.創(chuàng)建FileDescriptor實(shí)例來表示文件連接
    3.native方法open
}
// 使用文件系統(tǒng)的現(xiàn)有文件連接來創(chuàng)建
public FileInputStream(FileDescriptor fdObj)

• 核心方法

核心：私有的本地readBytes方法

private native int readBytes(byte b[], int off, int len) throws IOException;

public int read(byte b[]) throws IOException
public int read(byte b[], int off, int len)

public void close() throws IOException

• 其他方法

public native long skip(long n) throws IOException;
public native int available() throws IOException;
public final FileDescriptor getFD() throws IOException
public FileChannel getChannel()

2.FileOutputStream

• 構(gòu)造器

//實(shí)際調(diào)用FileOutputStream(File file, boolean append) 
public FileOutputStream(String name) throws FileNotFoundException
public FileOutputStream(String name, boolean append)
public FileOutputStream(File file) throws FileNotFoundException

public FileOutputStream(File file, boolean append) throws FileNotFoundException{
    1.文件安全及權(quán)限檢查
    2.創(chuàng)建FileDescriptor實(shí)例來表示文件連接
    3.native方法open
}
// 使用文件系統(tǒng)的現(xiàn)有文件連接來創(chuàng)建
public FileOutputStream(FileDescriptor fdObj)

• 核心方法

核心：私有的本地writeBytes方法

private native void writeBytes(byte b[], int off, int len, boolean append)

public void write(byte b[]) throws IOException
public void write(byte b[], int off, int len)

public void close() throws IOException

• 其他方法

public final FileDescriptor getFD() throws IOException
public FileChannel getChannel()

3.demo

最常見的功能：用FileInputStream和FileOutputStream復(fù)制文件

注：JDK7新增try-with-resources語法，將資源放入try()內(nèi)萝风，就不用手動close()了嘀掸。

    try (
                InputStream is = new FileInputStream("D:\\fileTest\\app.properties");
                // InputStream is=new FileInputStream(new File("D:\\fileTest\\app.properties"));
                OutputStream os = new FileOutputStream("D:\\fileTest\\out.properties");
        ) {
            byte[] bytes=new byte[1024];
            int len=0;
            while ((len=is.read(bytes))!=-1){
                os.write(bytes,0,len);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

二紫岩、文件字符流

在研究FileReader和FileWriter之前规惰，有必要先了解其父類。

1.InputStreamReader

底層StreamDecoder

• 構(gòu)造器（必須以InputStream為入?yún)ⅲ?/strong>

// 實(shí)際調(diào)用 StreamDecoder的構(gòu)造器
public InputStreamReader(InputStream in)
public InputStreamReader(InputStream in, String charsetName)
public InputStreamReader(InputStream in, Charset cs)
public InputStreamReader(InputStream in, CharsetDecoder dec)

public int read(char cbuf[], int offset, int length) throws IOException

public int read() throws IOException

public void close() throws IOException

public boolean ready() throws IOException
public String getEncoding()

public FileReader(String fileName) throws FileNotFoundException
public FileReader(File file) throws FileNotFoundException
public FileReader(FileDescriptor fd)

// 實(shí)際調(diào)用 StreamEncoder的構(gòu)造器
public OutputStreamWriter(OutputStream out)
public OutputStreamWriter(OutputStream out, String charsetName)
public OutputStreamWriter(OutputStream out, Charset cs)
public OutputStreamWriter(OutputStream out, CharsetEncoder enc)

public void write(String str, int off, int len) throws IOException
public void write(char cbuf[], int off, int len) throws IOException
public void write(int c) throws IOException

public void flush() throws IOException{
    1.flushBuffer()
    2.flush輸出流
}
public void close() throws IOException

void flushBuffer() throws IOException
public String getEncoding()

public FileWriter(String fileName) throws IOException
public FileWriter(String fileName, boolean append) throws IOException
public FileWriter(File file) throws IOException
public FileWriter(File file, boolean append) throws IOException
public FileWriter(FileDescriptor fd)

    try(
                FileReader fileReader=new FileReader("D:\\fileTest\\app.properties");
                FileWriter fileWriter=new FileWriter("D:\\fileTest\\out2.properties")
        ) {
            char[] chars=new char[1024];
            int len=0;
            while ((len=fileReader.read(chars))!=-1){
                fileWriter.write(chars,0,len);
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

InputStreamReader reader=new InputStreamReader(new FileInputStream("D:\\fileTest\\app.properties"));
Properties properties=new Properties();
properties.load(reader);
properties.forEach((k,v)-> System.out.println(k+":"+v));