Java中如何以二进制字节的方式来处理文件，前面我们提到Java中有流的概念，以二进制方式读写的主要流有：❑ InputStream/OutputStream：这是基类，它们是抽象类。❑ FileInputStream/FileOutputStream：输入源和输出目标是文件的流。❑ ByteArrayInputStream/ByteArrayOutputStream：输入源和输出目标是字节数组的流。❑ DataInputStream/DataOutputStream：装饰类，按基本类型和字符串而非只是字节读写流。❑ BufferedInputStream/BufferedOutputStream：装饰类，对输入输出流提供缓冲功能。下面，我们就来介绍这些类的功能、用法、原理和使用场景，最后总结一些简单的实用方法。
下面举个列子
package com.wcfb.model.po;
import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;
import java.io.Serializable;
/**
* @author wcfb
* @time 2021/5/8/008.
* @since
*/
@Data
@Builder
@NoArgsConstructor
@AllArgsConstructor
public class StudentPO implements Serializable {
private String name;
private int age;
private int sex;
}
package com.wcfb;
import com.wcfb.model.po.StudentPO;
import org.junit.jupiter.api.Test;
import org.springframework.boot.test.context.SpringBootTest;
import java.io.*;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**
* @author wcfb
* @time 2021/5/8/008.
* @desc 文件流测试
* @since 1.0
*/
@SpringBootTest
public class FileTestApplication {
/**
* 写内容到文件
*
* @throws IOException
*/
@Test
public void test1() throws IOException {
OutputStream outputStream = new FileOutputStream("text.txt");
StringBuilder stringBuilder = new StringBuilder();
for (int i = 0; i < 1000; i++) {
stringBuilder.append("hello io ").append(i).append("\n");
}
String data = stringBuilder.toString();
byte[] bytes = data.getBytes(StandardCharsets.UTF_8);
try {
outputStream.write(bytes);
} catch (IOException e) {
e.printStackTrace();
} finally {
outputStream.close();
}
}
/**
* 读取文件内容（固定长度）
*
* @throws IOException
*/
@Test
public void test2() throws IOException {
InputStream inputStream = new FileInputStream("text.txt");
byte[] buf = new byte[1024];
try {
int byteRead = inputStream.read(buf);
String data = new String(buf, 0, byteRead, StandardCharsets.UTF_8);
System.out.println(data);
} catch (Exception e) {
e.printStackTrace();
} finally {
inputStream.close();
}
}
/**
* 读取所有内容
*/
@Test
public void test3() throws Exception {
InputStream inputStream = new FileInputStream("text.txt");
byte[] buf = new byte[1024];
int byteRead = -1;
while ((byteRead = inputStream.read(buf)) != -1) {
String data = new String(buf, 0, byteRead, StandardCharsets.UTF_8);
System.out.println(data);
}
}
/**
* 保存对象
*
* @throws FileNotFoundException
*/
@Test
public void test4() throws Exception {
List<StudentPO> studentList = Arrays.asList(
new StudentPO("小红", 16, 0),
new StudentPO("小兰", 17, 1),
new StudentPO("小黑", 22, 1)
);
DataOutput dataOutput = new DataOutputStream(new FileOutputStream("student.txt"));
for (StudentPO s : studentList) {
dataOutput.writeUTF(s.getName());
dataOutput.writeInt(s.getAge());
dataOutput.writeInt(s.getSex());
}
}
/**
* 读取对象(文件流格式)
*/
@Test
public void test5() throws Exception {
DataInput input = new DataInputStream(new FileInputStream("student.txt"));
List<StudentPO> studentList = new ArrayList<>();
for (int i = 0; i < 3; i++) {
studentList.add(new StudentPO(input.readUTF(), input.readInt(), input.readInt()));
}
studentList.forEach(System.out::println);
}
/**
* 使用writer
*/
@Test
public void test6() throws Exception {
Writer writer = new OutputStreamWriter(new FileOutputStream("student.txt"), StandardCharsets.UTF_8);
String data = "hello io 试试";
try {
writer.write(data);
} catch (Exception e) {
e.printStackTrace();
} finally {
writer.close();
}
}
/**
* 使用reader
*/
@Test
public void test7() throws Exception {
Reader reader = new InputStreamReader(new FileInputStream("student.txt"), StandardCharsets.UTF_8);
try {
char[] cbuf = new char[1024];
int chatsRead = reader.read(cbuf);
System.out.println(new String(cbuf, 0, chatsRead));
} catch (Exception e){
e.printStackTrace();
} finally {
reader.close();
}
}
/**
* fileWriter使用
*
* @throws Exception
*/
@Test
public void test8() throws Exception {
Writer writer = new FileWriter("student.txt");
try {
writer.write("writer is ok a");
} catch (Exception e) {
e.printStackTrace();
} finally {
writer.close();
}
}
/**
* 使用 fileReader
*
* @throws Exception
*/
@Test
public void test9() throws Exception {
Reader reader = new FileReader(new File("student.txt"));
try {
char[] chars = new char[1024];
int read = reader.read(chars);
System.out.println(new String(chars));
} catch (Exception e) {
e.printStackTrace();
} finally {
}
}
/**
* fileWriter使用
*
* @throws Exception
*/
@Test
public void test8() throws Exception {
Writer writer = new FileWriter("student.txt");
try {
writer.write("writer is ok a");
} catch (Exception e) {
e.printStackTrace();
} finally {
writer.close();
}
Reader reader = new FileReader(new File("student.txt"));
try {
char[] chars = new char[1024];
int read = reader.read(chars);
System.out.println(new String(chars));
} catch (Exception e) {
e.printStackTrace();
} finally {
}
}
/**
* 使用bufferWriter
*
* @throws Exception
*/
@Test
public void test10() throws Exception {
BufferedWriter writer = new BufferedWriter(new FileWriter("student.txt"));
try {
writer.write("你好，" + "hhhh 哈哈哈\n guguhhhh ");
writer.newLine();
} catch (Exception e) {
e.printStackTrace();
} finally {
writer.close();
}
BufferedReader reader = new BufferedReader(new FileReader("student.txt"));
try {
String s = null;
while ((s = reader.readLine()) != null) {
System.out.println(s);
}
} catch (Exception e) {
e.printStackTrace();
} finally {
reader.close();
}
}
}
用例1 生成的文件对应的截图如下
image.png
用例2生成的截图如下
image.png
用例3的截图如下
image.png
用例6的截图如下
image.png
用例7的截图如下
image.png
小结
本节介绍了如何在Java中以字符流的方式读写文本文件，我们强调了二进制思维、文本文本与二进制文件的区别、编码，以及字符流与字节流的不同，介绍了个各种字符流、Scanner以及标准流，最后总结了一些实用方法。写文件时，可以优先考虑PrintWriter，因为它使用方便，支持自动缓冲、指定编码类型、类型转换等。读文件时，如果需要指定编码类型，需要使用InputStreamReader；如果不需要指定编码类型，可使用FileReader，但都应该考虑在外面包上缓冲类Buffered-Reader。
