Java读写文件常用方法
一.字符流：读写纯文本（txt，csv等），
1 字符流写文件主要用：FileWriter，BufferedWriter，PrintWriter
1.1 测试 FileWriter 写入
private void writeFileWriter() throws IOException {
try (FileWriter fw = new FileWriter(basicPath + "writeUnicode_FileWriter.txt")) {
fw.write("测试 FileWriter 写入。");
}
}
1.2 测试 BufferedWriter 写入
private void writeBufferedWriter() throws IOException {
try (BufferedWriter bw = new BufferedWriter(new FileWriter(basicPath + "writeUnicode_BufferedWriter.txt"))) {
bw.write("测试 BufferedWriter 写入。");
}
}
1.3 测试 PrintWriter 写入
private void writePrintWriter() throws IOException {
try (PrintWriter pw = new PrintWriter(new FileWriter(basicPath + "writeUnicode_PrintWriter.txt"))) {
pw.write("测试 PrintWriter 写入。");
}
}
2 字符流读文件主要用：FileReader，BufferedReader
2.1 测试 FileReader 读取
private void readFileReader() throws IOException {
// 方式1：一个一个char读取 （不推荐）
try (FileReader fr = new FileReader(basicPath + "writeUnicode_FileWriter.txt")) {
int ch;
while ((ch = fr.read()) != -1) {
System.out.print((char) ch);
}
}
// 方式2：数组自定长度一次性读取
try (FileReader fr = new FileReader(basicPath + "writeUnicode_FileWriter.txt")) {
char[] buf = new char[1024];
int length;
while ((length = fr.read(buf)) != -1) {
String str = new String(buf, 0, length);
System.out.print(str);
}
}
}
2.2测试 BufferedReader 读取
private void readBufferedReader() throws IOException {
// 方式1：一个一个char读取 （不推荐）
try (BufferedReader br = new BufferedReader(new FileReader(basicPath + "writeUnicode_BufferedWriter.txt"))) {
int c;
while ((c = br.read()) != -1) {
System.out.print((char) c);
}
}
// 方式2：数组自定长度一次性读取
try (BufferedReader br = new BufferedReader(new FileReader(basicPath + "writeUnicode_BufferedWriter.txt"))) {
char[] buf = new char[1024];
int length;
while ((length = br.read(buf)) != -1) {
String str = new String(buf, 0, length);
System.out.print(str);
}
}
// 方式3：bufferedReader.readLine()读取
try (BufferedReader br = new BufferedReader(new FileReader(basicPath + "writeUnicode_BufferedWriter.txt"))) {
String line;
while ((line = br.readLine()) != null) {
System.out.print(line);
}
}
}
二.字节流：读取视频，音频，二进制文件等，（文本文件也可以但不推荐，以下仅为测试用）
1 字节流写文件主要用：FileOutputStream，BufferedOutputStream
1.1 测试 FileOutputStream 写入
private void writeFileOutputStream() throws IOException {
try (FileOutputStream fos = new FileOutputStream(basicPath + "writeByte_FileOutputStream.txt")) {
String content = "测试 FileOutputStream 写入。";
byte[] bytes = content.getBytes();
fos.write(bytes);
}
}
1.2 测试 BufferedOutputStream 写入
private void writeBufferedOutputStream() throws IOException {
try (BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(basicPath + "writeByte_BufferedOutputStream.txt"))) {
String content = "测试 BufferedOutputStream 写入。";
byte[] bytes = content.getBytes();
bos.write(bytes);
}
}
2 字节流读文件主要用：FileInputStream，BufferedInputStream
2.1 测试 FileInputStream 读取
private void readFileInputStream() throws IOException {
// 方式1：一个一个char读取 （不推荐，且中文占2个字节，此方式读中文文件会造成乱码）
try (FileInputStream fis = new FileInputStream(basicPath + "writeByte_FileOutputStream.txt")) {
int ch;
while ((ch = fis.read()) != -1) {
System.out.print((char) ch);
}
}
// 方式2：数组自定长度一次性读取
try (FileInputStream fis = new FileInputStream(basicPath + "writeByte_FileOutputStream.txt")) {
byte[] buf = new byte[1024];
int length;
while ((length = fis.read(buf)) != -1) {
String str = new String(buf, 0, length);
System.out.print(str);
}
}
}
2.2 测试 BufferedInputStream 读取
private void readBufferedInputStream() throws IOException {
// 方式1：一个一个char读取 （不推荐，且中文占2个字节，此方式读中文文件会造成乱码）
try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(basicPath + "writeByte_BufferedOutputStream.txt"))) {
int c;
while ((c = bis.read()) != -1) {
System.out.print((char) c);
}
}
// 方式2：数组自定长度一次性读取
try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(basicPath + "writeByte_BufferedOutputStream.txt"))) {
byte[] buf = new byte[1024];
int length;
while ((length = bis.read(buf)) != -1) {
String str = new String(buf, 0, length);
System.out.print(str);
}
}
}
三.通过 Files类读写文件
1 测试 Files类写入
private void writeFiles() throws IOException {
String content = "测试 Files 类写入。\n第二行";
Files.write(Paths.get(basicPath + "writeFiles.txt"), content.getBytes());
}
2 测试 Files类读取
private void readFiles() throws IOException {
// 方式1 （文件特大时会占满内存）
byte[] bytes = Files.readAllBytes(Paths.get(basicPath + "writeFiles.txt"));
String srcStr1 = new String(bytes);
System.out.println(srcStr1);
// 方式2 （文件特大时会占满内存）
List<String> lines = Files.readAllLines(Paths.get(basicPath + "writeFiles.txt"));
StringBuilder sb = new StringBuilder();
for (String line : lines) {
// 此时line最后没有换行，因为readAllLines以换行分隔了所有行，可以用System.out.print 看到效果
sb.append(line).append("\n");
}
String srcStr2 = sb.toString();
System.out.println(srcStr2);
// 方式3 JDK8的Stream流，边消费边读取
String srcStr3 = Files.lines(Paths.get(basicPath + "writeFiles.txt")).reduce((s1, s2) -> s1 + s2).get();
System.out.println(srcStr3);
}
四.源码
1 字符流读写
package com.writefiles; import java.io.*; /**
* @author: Convict.Yellow
* @date: 2020/12/22 16:11
* @description: 字符流的基本单位为 Unicode，大小为两个字节（Byte），主要用来处理文本数据。
* 字符流有两个基类：Reader（输入字符流）和 Writer（输出字符流）。
* <p>
* 字符流写文件主要用：FileWriter，BufferedWriter，PrintWriter
* 字符流读文件主要用：FileReader，BufferedReader
*/
public class WriteAndReadByUnicode { private static final String basicPath = "D:/ztest/"; public static void main(String[] args) throws IOException {
WriteAndReadByUnicode entrance = new WriteAndReadByUnicode(); // 测试 FileWriter 写入
entrance.writeFileWriter();
// 测试 BufferedWriter 写入
entrance.writeBufferedWriter();
// 测试 PrintWriter 写入
entrance.writePrintWriter(); // 测试 FileReader 读取
entrance.readFileReader();
// 测试 BufferedReader 读取
entrance.readBufferedReader();
} private void writeFileWriter() throws IOException {
try (FileWriter fw = new FileWriter(basicPath + "writeUnicode_FileWriter.txt")) {
fw.write("测试 FileWriter 写入。");
}
} private void writeBufferedWriter() throws IOException {
try (BufferedWriter bw = new BufferedWriter(new FileWriter(basicPath + "writeUnicode_BufferedWriter.txt"))) {
bw.write("测试 BufferedWriter 写入。");
}
} private void writePrintWriter() throws IOException {
try (PrintWriter pw = new PrintWriter(new FileWriter(basicPath + "writeUnicode_PrintWriter.txt"))) {
pw.write("测试 PrintWriter 写入。");
}
} private void readFileReader() throws IOException {
// 方式1：一个一个char读取 （不推荐）
try (FileReader fr = new FileReader(basicPath + "writeUnicode_FileWriter.txt")) {
int ch;
while ((ch = fr.read()) != -1) {
System.out.print((char) ch);
}
} // 方式2：数组自定长度一次性读取
try (FileReader fr = new FileReader(basicPath + "writeUnicode_FileWriter.txt")) {
char[] buf = new char[1024];
int length;
while ((length = fr.read(buf)) != -1) {
String str = new String(buf, 0, length);
System.out.print(str);
}
}
} private void readBufferedReader() throws IOException {
// 方式1：一个一个char读取 （不推荐）
try (BufferedReader br = new BufferedReader(new FileReader(basicPath + "writeUnicode_BufferedWriter.txt"))) {
int c;
while ((c = br.read()) != -1) {
System.out.print((char) c);
}
} // 方式2：数组自定长度一次性读取
try (BufferedReader br = new BufferedReader(new FileReader(basicPath + "writeUnicode_BufferedWriter.txt"))) {
char[] buf = new char[1024];
int length;
while ((length = br.read(buf)) != -1) {
String str = new String(buf, 0, length);
System.out.print(str);
}
} // 方式3：bufferedReader.readLine()读取
try (BufferedReader br = new BufferedReader(new FileReader(basicPath + "writeUnicode_BufferedWriter.txt"))) {
String line;
while ((line = br.readLine()) != null) {
System.out.print(line);
}
}
} }
2 字节流读写
package com.writefiles; import java.io.*; /**
* @author: Convict.Yellow
* @date: 2020/12/22 15:27
* @description: 字节流的基本单位为字节（Byte），一个字节为8位（bit），主要是用来处理二进制（数据）。
* 字节流有两个基类：InputStream（输入字节流）和 OutputStream（输出字节流）。
* <p>
* 字节流写文件主要用：FileOutputStream，BufferedOutputStream
* 字节流读文件主要用：FileInputStream，BufferedInputStream
*/
public class WriteAndReadByByte { private static final String basicPath = "D:/ztest/"; public static void main(String[] args) throws IOException {
WriteAndReadByByte entrance = new WriteAndReadByByte(); // 测试 FileOutputStream 写入
entrance.writeFileOutputStream();
// 测试 BufferedOutputStream 写入
entrance.writeBufferedOutputStream(); // 测试 FileInputStream 读取
entrance.readFileInputStream();
// 测试 BufferedInputStream 读取
entrance.readBufferedInputStream(); } private void writeFileOutputStream() throws IOException {
try (FileOutputStream fos = new FileOutputStream(basicPath + "writeByte_FileOutputStream.txt")) {
String content = "测试 FileOutputStream 写入。";
byte[] bytes = content.getBytes();
fos.write(bytes);
}
} private void writeBufferedOutputStream() throws IOException {
try (BufferedOutputStream bos = new BufferedOutputStream(new FileOutputStream(basicPath + "writeByte_BufferedOutputStream.txt"))) {
String content = "测试 BufferedOutputStream 写入。";
byte[] bytes = content.getBytes();
bos.write(bytes);
}
} private void readFileInputStream() throws IOException {
// 方式1：一个一个char读取 （不推荐，且中文占2个字节，此方式读中文文件会造成乱码）
try (FileInputStream fis = new FileInputStream(basicPath + "writeByte_FileOutputStream.txt")) {
int ch;
while ((ch = fis.read()) != -1) {
System.out.print((char) ch);
}
} // 方式2：数组自定长度一次性读取
try (FileInputStream fis = new FileInputStream(basicPath + "writeByte_FileOutputStream.txt")) {
byte[] buf = new byte[1024];
int length;
while ((length = fis.read(buf)) != -1) {
String str = new String(buf, 0, length);
System.out.print(str);
}
}
} private void readBufferedInputStream() throws IOException {
// 方式1：一个一个char读取 （不推荐，且中文占2个字节，此方式读中文文件会造成乱码）
try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(basicPath + "writeByte_BufferedOutputStream.txt"))) {
int c;
while ((c = bis.read()) != -1) {
System.out.print((char) c);
}
} // 方式2：数组自定长度一次性读取
try (BufferedInputStream bis = new BufferedInputStream(new FileInputStream(basicPath + "writeByte_BufferedOutputStream.txt"))) {
byte[] buf = new byte[1024];
int length;
while ((length = bis.read(buf)) != -1) {
String str = new String(buf, 0, length);
System.out.print(str);
}
}
} }
3 Files类读写
package com.writefiles; import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List; /**
* @author: Convict.Yellow
* @date: 2020/12/22 16:11
* @description:
*
*/
public class WriteAndReadByFiles { private static final String basicPath = "D:/ztest/"; public static void main(String[] args) throws IOException {
WriteAndReadByFiles entrance = new WriteAndReadByFiles(); // 测试 Files类写入
entrance.writeFiles(); // 测试 Files类读取
entrance.readFiles();
} private void writeFiles() throws IOException {
String content = "测试 Files 类写入。\n第二行";
Files.write(Paths.get(basicPath + "writeFiles.txt"), content.getBytes());
} private void readFiles() throws IOException {
// 方式1 （文件特大时会占满内存）
byte[] bytes = Files.readAllBytes(Paths.get(basicPath + "writeFiles.txt"));
String srcStr1 = new String(bytes);
System.out.println(srcStr1); // 方式2 （文件特大时会占满内存）
List<String> lines = Files.readAllLines(Paths.get(basicPath + "writeFiles.txt"));
StringBuilder sb = new StringBuilder();
for (String line : lines) {
// 此时line最后没有换行，因为readAllLines以换行分隔了所有行，可以用System.out.print 看到效果
sb.append(line).append("\n");
}
String srcStr2 = sb.toString();
System.out.println(srcStr2); // 方式3 JDK8的Stream流，边消费边读取
String srcStr3 = Files.lines(Paths.get(basicPath + "writeFiles.txt")).reduce((s1, s2) -> s1 + s2).get();
System.out.println(srcStr3);
} }
Tip：均采用 try-with-resources写法，故无需手动 close流，try-with-resources写法可参考此处。
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