java读取文件(更新jdk7及jdk8)

以字节的方式读取：

            InputStream inputStream = new FileInputStream(file);
            int temp = -1;
            StringBuilder sb = new StringBuilder();
            while((temp = inputStream.read()) != -1){
                sb.append((char)temp);
            }
            inputStream.close();

也可以多个字节一起读取：

            InputStream inputStream = new FileInputStream(file);
            byte[] bytes = new byte[10];
            StringBuilder sb = new StringBuilder();
            int length = -1;
            while((length = inputStream.read(bytes))!= -1){
                sb.append(new String(bytes,0,length,Charset.forName("utf-8")));
            }
            inputStream.close();

以字符的方式读取：

            InputStream inputStream = new FileInputStream(file);
            InputStreamReader isr = new InputStreamReader(inputStream,Charset.forName("utf-8"));
            StringBuilder sb = new StringBuilder();
            int temp = -1;
            while((temp = (isr.read()))!= -1){
                sb.append((char)temp);
            }
            inputStream.close();
            isr.close();

或者用封装的BufferedReader按行读取，效率更高：

InputStream inputStream = new FileInputStream(file);
            InputStreamReader isr = new InputStreamReader(inputStream,Charset.forName("utf-8"));
            BufferedReader bufferedReader = new BufferedReader(isr);
            StringBuilder sb = new StringBuilder();
            String line = null;
            while((line = bufferedReader.readLine())!=null){
                sb.append(line + '\n');
            }
            inputStream.close();
            isr.close();
            bufferedReader.close();

-----------------------------------------------以上是jdk7之前一般使用的读取文件方法-------------------------------------------------------------------------------------------------------

jdk7引入了新的文件api: java.nio.file.Files。 Files.readAllBytes()方法将文件内容全部读入内存，并且确保读取完之后文件是关闭的，也就是说，不用手动调用close方法:

String path = "C:\\test.txt";
System.out.print(Files.readAllBytes(Paths.get(path)));

当文件过大时，不建议使用readAllBytes()方法将文件内容一次全部读入到内存里面。

java8中使用流的方式来读取更高效：

Files.lines(Paths.get(path),StandardCharsets.UTF_8).forEach(System.out::println);