java读取文件

1、字节形式读取

@Test
public void test1(){
    String path = "d://temp/test.txt";
    readFile(path);
}

private void readFile(String path) {
    //FileInputStream 用于读取诸如图像数据之类的原始字节流。要读取字符流，请考虑使用 FileReader
    File file = new File(path);
    InputStream in = null;
    try {
        in = new FileInputStream(file);
        int tempStr = 0;
        while((tempStr = in.read())!=-1){
            System.out.write(tempStr);
        }
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } 
}

改进方式一次读取多个字节

private void readFile(String path) {
    //FileInputStream 用于读取诸如图像数据之类的原始字节流。要读取字符流，请考虑使用 FileReader
    File file = new File(path);
    InputStream in = null;
    try {
        in = new FileInputStream(file);
        byte[] byteArr = new byte[1024];
        while(in.read(byteArr)!=-1){
            System.out.write(byteArr);
        }
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } 
}

2、字符形式读取

private void readFile(String path) {
    File file = new File(path);
    InputStreamReader in = null;
    try {
        in = new InputStreamReader(new FileInputStream(file));
        int tempStr;
        while((tempStr=in.read())!=-1){
            System.out.write(tempStr);
        }
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } finally {
        if(in!=null)
            try {
                in.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
    }
}

改进方式

private void readFile(String path) {
    File file = new File(path);
    InputStreamReader in = null;
    try {
        in = new InputStreamReader(new FileInputStream(file));
        char[] charArr = new char[1024];
        while(in.read(charArr)!=-1){
            System.out.print(charArr);
        }
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } finally {
        if(in!=null)
            try {
                in.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
    }
}

3、以行为单位读取文件，常用于读面向行的格式化文件，如csv等

private void readFile(String path) {
    File file = new File(path);
    BufferedReader in = null;
    try {
        in = new BufferedReader(new FileReader(file));
        String tempStr = "";
        while((tempStr=in.readLine()) != null){
            System.out.println(tempStr);
        }
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } finally {
        if(in!=null)
            try {
                in.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
    }
}