步骤：

1.引入相关的类           import java.io.IOException;

​                       import java.io.FileInputStream;

2.构造文件输入流**FileInputStream** 对象    
FileInputStream fis= new FileInputStream(“c:\\test.txt");
 
3.读取文本文件的数据     fis.available(); 

​                       fis.read();

4.关闭文件流对象 fis.close();
@Test
    public void test01(){
        //1.创建File类
        File  file = new File("HelloWorld.txt");
        //2.创建合适的流
        FileInputStream  fis=null;
        try {
              fis = new FileInputStream(file);
                //3.读操作
            //调用FileInputStream  中的read()方法，一个一个字节的去读内容
            //直到读取到最后一个内容的时候  返回  -1
            int len = fis.read();
            while(len!=-1){
                //返回值不为-1则循环读取文件中内容并打印
                System.out.print((char)len);
                len=fis.read();
                
            }
            
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            //4.关闭流
            try {
                fis.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        
        
        
    }          

/**
     *  boolean exists( )              是否存在
     *  boolean delete( )              删除
     *  boolean createNewFile( )   创建一个新的文件
     *  boolean isFile( )               是否为文件
     *  boolean isDirectory( )      是否为文件夹
     *  String getPath( )             获取路径
     *  String getAbsolutePath( )  获取绝对路径
     *  String getName( )           获取名字 
     *  long length()                  获取文件中内容长度
     */
@Test
    public void test01() {
        // D:\workspace\KH87\workspace\HelloWorld\hello.txt

        // 创建两个File对象
        File f1 = new File("D:\\workspace\\KH87\\workspace\\HelloWorld\\hello.txt");
        File f2 = new File("HelloWorld.txt");

        System.out.println(f1.isFile());
        System.out.println(f1.isDirectory( ));
        System.out.println(f1.getPath( ));
        System.out.println(f1.getAbsolutePath( ));
        System.out.println(f1.getName( ));
        System.out.println(f1.length());
        
        
        System.out.println("=============");
        System.out.println(f2.isFile());
        System.out.println(f2.isDirectory( ));
        System.out.println(f2.getPath( ));
        System.out.println(f2.getAbsolutePath( ));
        System.out.println(f2.getName( ));
        System.out.println(f2.length());
    
    @Test
    public void test02(){
        File  file = new File("HelloWorld.txt");
        if(file.exists()){
            //如果存在则删除
            file.delete();
            System.out.println("删除成功");
            
            
        }else {
            //不存在  创建
            try {
                file.createNewFile();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("文件创建成功");
            
        }

public class TestOutnput {
    @Test
    public void tset01() {
        File file=new File("word.txt");
        FileOutputStream out=null;
        try {
            out=new FileOutputStream(file);
            out.write("Hello".getBytes());
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            try {
                out.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            
        }

@Test
    public void tset02() {
        
        
        File file1=new File("Hello.txt");
        
        File file2=new File("word.txt");
        FileInputStream f1=null;
        FileOutputStream f2=null;
        try {
             f1 =new FileInputStream(file1);
            f2=new FileOutputStream(file2);
            
            byte [] aaa=new byte[30];
             int read;
             while((read=f1.read(aaa))!=-1){
             
            f2.write(aaa, 0, read);
             }
            
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            try {
                f1.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }finally{
                
                try {
                    f2.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }

public class TestReader {
    @Test
    public void tset01()  {
        File file1=new File("Hello.txt");
        File file2=new File("Hello1.txt");
        FileReader f1=null;
        FileWriter f2=null;
        try {
            f1=new FileReader(file1);
            
             f2=new FileWriter(file2);
            
                char [] abc=new char[30];
                 int len;
                    while((len=f1.read(abc))!=-1){
                        
                        f2.write(abc);
                    }
                 
            
             
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            try {
                f1.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }finally{
                try {
                    f2.close();
                } catch (IOException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }
        
    }