Java—从文件中读取数据

1、FileInputStream（）

              // 构建字节输入流对象，参数为文件名
              FileInputStream fin = new FileInputStream("message");
              System.out.println("输入流可读入字节数：" + fin.available());
              // 建立byte型数组b,从输入流读取的数据暂时存放在b中
              byte b[] = new byte[fin.available()];
              // 从输入流读取数据
              fin.read(b);
              String str5=new String(b);
              System.out.println(str5);
              // 关闭输入流，对文件的操作，一定要在最后关闭输入输出流
              fin.close();

2、RandomAccessFile（）

              String str6="";
              ArrayList<String> strs=new ArrayList<String>();
              RandomAccessFile file=new RandomAccessFile("message","r");
              str6 = file.readLine();
              while(str6!=null){
                  strs.add(str6);
                  str6 = file.readLine();
              }
              for(int j=0;j<strs.size();j++){
                  System.out.println(strs.get(j));
              }
              file.close();

3、File

              File file2=new File("message");
              if(file2.exists()&&file2.isFile()){
                  InputStream is=new FileInputStream(file2);
                  byte[] buf = new byte[is.available()];
                  System.out.println(is.available());
                   while(is.read(buf)!=-1){
                  //每次读取打印
                      System.out.println(new String(buf));
                  }
              }

4、避免乱码

            File file3 = new File("message");
            if (file3.exists() && file3.isFile()) {
                try {
                    InputStream is = new FileInputStream(file3);
                    InputStreamReader reader = new InputStreamReader(is,"utf-8");//
                    char[] cbuf = new char[is.available()];//字符，字节

                    StringBuffer sb2=new StringBuffer();//2
                    while (reader.read(cbuf) != -1) {
                        sb2.append(cbuf);
                    }
                    System.out.println(sb2.toString());

                } catch (Exception e) {

                }
            }

5、BufferedReader

            File file = new File("message");
            try {
                InputStream is = new FileInputStream(file);
                if (file.exists() && file.isFile()) {
                    BufferedReader br = new BufferedReader(
                            new InputStreamReader(is, "utf-8"));
                    StringBuffer sb2 = new StringBuffer();
                    String line = null;
                    while ((line = br.readLine()) != null) {
                        sb2.append(line + "\n");
                    }
                    br.close();
                    System.out.println(sb2.toString());
                }
            } catch (Exception e) {

            }