Streams
文件信息
- 📄 原文件：
Streams.java - 🔤 语言：java
Java I/O 流详解 本文件介绍 Java 中各种 I/O 流的使用。
完整代码
java
import java.io.*;
import java.nio.charset.StandardCharsets;
import java.util.zip.*;
/**
* ============================================================
* Java I/O 流详解
* ============================================================
* 本文件介绍 Java 中各种 I/O 流的使用。
* ============================================================
*/
public class Streams {
public static void main(String[] args) throws IOException {
streamHierarchy();
byteStreams();
characterStreams();
bufferedStreams();
dataStreams();
objectStreams();
compressionStreams();
}
/**
* ============================================================
* 1. 流的层次结构
* ============================================================
*/
public static void streamHierarchy() {
System.out.println("=".repeat(60));
System.out.println("1. 流的层次结构");
System.out.println("=".repeat(60));
System.out.println("""
【字节流】处理二进制数据
InputStream
├── FileInputStream - 文件输入
├── ByteArrayInputStream - 字节数组输入
├── BufferedInputStream - 缓冲输入
├── DataInputStream - 基本类型输入
├── ObjectInputStream - 对象输入
└── ...
OutputStream
├── FileOutputStream - 文件输出
├── ByteArrayOutputStream - 字节数组输出
├── BufferedOutputStream - 缓冲输出
├── DataOutputStream - 基本类型输出
├── ObjectOutputStream - 对象输出
└── ...
【字符流】处理文本数据
Reader
├── FileReader - 文件读取
├── StringReader - 字符串读取
├── BufferedReader - 缓冲读取
├── InputStreamReader - 字节转字符
└── ...
Writer
├── FileWriter - 文件写入
├── StringWriter - 字符串写入
├── BufferedWriter - 缓冲写入
├── OutputStreamWriter - 字符转字节
├── PrintWriter - 格式化输出
└── ...
【装饰器模式】
可以嵌套使用多个流来增强功能：
new BufferedReader(new InputStreamReader(
new FileInputStream("file.txt"), StandardCharsets.UTF_8))
""");
}
/**
* ============================================================
* 2. 字节流
* ============================================================
*/
public static void byteStreams() throws IOException {
System.out.println("\n" + "=".repeat(60));
System.out.println("2. 字节流");
System.out.println("=".repeat(60));
String filename = "byte_test.bin";
// 【FileOutputStream】
System.out.println("--- FileOutputStream ---");
try (FileOutputStream fos = new FileOutputStream(filename)) {
// 写入单个字节
fos.write(65); // 'A'
fos.write(66); // 'B'
fos.write(67); // 'C'
// 写入字节数组
byte[] data = {68, 69, 70}; // 'D', 'E', 'F'
fos.write(data);
// 写入部分数组
byte[] more = {71, 72, 73, 74, 75};
fos.write(more, 1, 3); // 'H', 'I', 'J'
System.out.println("写入完成");
}
// 【FileInputStream】
System.out.println("\n--- FileInputStream ---");
try (FileInputStream fis = new FileInputStream(filename)) {
// 读取单个字节
int b;
System.out.print("逐字节读取: ");
while ((b = fis.read()) != -1) {
System.out.print((char) b);
}
System.out.println();
}
// 读取到数组
try (FileInputStream fis = new FileInputStream(filename)) {
byte[] buffer = new byte[4];
int bytesRead;
System.out.print("按块读取: ");
while ((bytesRead = fis.read(buffer)) != -1) {
System.out.print(new String(buffer, 0, bytesRead));
}
System.out.println();
}
// 【ByteArrayOutputStream / ByteArrayInputStream】
System.out.println("\n--- ByteArray 流 ---");
ByteArrayOutputStream baos = new ByteArrayOutputStream();
baos.write("Hello, ByteArray!".getBytes());
byte[] result = baos.toByteArray();
System.out.println("ByteArrayOutputStream: " + new String(result));
ByteArrayInputStream bais = new ByteArrayInputStream(result);
System.out.print("ByteArrayInputStream: ");
int ch;
while ((ch = bais.read()) != -1) {
System.out.print((char) ch);
}
System.out.println();
// 清理
new File(filename).delete();
}
/**
* ============================================================
* 3. 字符流
* ============================================================
*/
public static void characterStreams() throws IOException {
System.out.println("\n" + "=".repeat(60));
System.out.println("3. 字符流");
System.out.println("=".repeat(60));
String filename = "char_test.txt";
// 【FileWriter / FileReader】
System.out.println("--- FileWriter / FileReader ---");
try (FileWriter fw = new FileWriter(filename, StandardCharsets.UTF_8)) {
fw.write("你好，世界！\n");
fw.write("Hello, World!\n");
}
try (FileReader fr = new FileReader(filename, StandardCharsets.UTF_8)) {
char[] buffer = new char[1024];
int charsRead = fr.read(buffer);
System.out.println("FileReader:\n" + new String(buffer, 0, charsRead));
}
// 【InputStreamReader / OutputStreamWriter】编码转换
System.out.println("--- 编码转换 ---");
try (OutputStreamWriter osw = new OutputStreamWriter(
new FileOutputStream(filename), StandardCharsets.UTF_8)) {
osw.write("使用 OutputStreamWriter 指定编码\n");
}
try (InputStreamReader isr = new InputStreamReader(
new FileInputStream(filename), StandardCharsets.UTF_8)) {
char[] buffer = new char[1024];
int charsRead = isr.read(buffer);
System.out.println("InputStreamReader: " + new String(buffer, 0, charsRead));
}
// 【StringWriter / StringReader】
System.out.println("--- StringWriter / StringReader ---");
StringWriter sw = new StringWriter();
sw.write("写入 StringWriter");
sw.append(" 追加内容");
System.out.println("StringWriter: " + sw.toString());
StringReader sr = new StringReader("从 StringReader 读取");
char[] chars = new char[50];
int len = sr.read(chars);
System.out.println("StringReader: " + new String(chars, 0, len));
// 清理
new File(filename).delete();
}
/**
* ============================================================
* 4. 缓冲流
* ============================================================
*/
public static void bufferedStreams() throws IOException {
System.out.println("\n" + "=".repeat(60));
System.out.println("4. 缓冲流");
System.out.println("=".repeat(60));
System.out.println("""
缓冲流优势：
- 减少实际 I/O 操作次数
- 提供便捷方法（如 readLine）
- 显著提升性能
""");
String filename = "buffered_test.txt";
// 【BufferedWriter / BufferedReader】
System.out.println("--- BufferedWriter / BufferedReader ---");
try (BufferedWriter bw = new BufferedWriter(
new FileWriter(filename, StandardCharsets.UTF_8))) {
bw.write("第一行");
bw.newLine(); // 平台无关的换行
bw.write("第二行");
bw.newLine();
bw.write("第三行");
System.out.println("BufferedWriter 完成");
}
try (BufferedReader br = new BufferedReader(
new FileReader(filename, StandardCharsets.UTF_8))) {
String line;
System.out.println("逐行读取:");
while ((line = br.readLine()) != null) {
System.out.println(" " + line);
}
}
// 【BufferedReader.lines() 返回 Stream】
System.out.println("\n--- BufferedReader.lines() ---");
try (BufferedReader br = new BufferedReader(
new FileReader(filename, StandardCharsets.UTF_8))) {
br.lines()
.map(String::toUpperCase)
.forEach(System.out::println);
}
// 【BufferedInputStream / BufferedOutputStream】
System.out.println("\n--- 缓冲字节流 ---");
String binFile = "buffered_bin.dat";
try (BufferedOutputStream bos = new BufferedOutputStream(
new FileOutputStream(binFile), 8192)) { // 指定缓冲区大小
for (int i = 0; i < 1000; i++) {
bos.write(i % 256);
}
System.out.println("BufferedOutputStream 完成");
}
try (BufferedInputStream bis = new BufferedInputStream(
new FileInputStream(binFile))) {
int count = 0;
while (bis.read() != -1) {
count++;
}
System.out.println("读取字节数: " + count);
}
// 清理
new File(filename).delete();
new File(binFile).delete();
}
/**
* ============================================================
* 5. 数据流
* ============================================================
*/
public static void dataStreams() throws IOException {
System.out.println("\n" + "=".repeat(60));
System.out.println("5. 数据流");
System.out.println("=".repeat(60));
System.out.println("""
DataInputStream/DataOutputStream:
- 读写 Java 基本数据类型
- 以二进制格式存储，跨平台
""");
String filename = "data_test.dat";
// 【写入基本类型】
try (DataOutputStream dos = new DataOutputStream(
new BufferedOutputStream(new FileOutputStream(filename)))) {
dos.writeInt(42);
dos.writeDouble(3.14159);
dos.writeBoolean(true);
dos.writeUTF("Hello, DataStream!"); // 写入 UTF-8 字符串
System.out.println("DataOutputStream 完成");
}
// 【读取基本类型】必须按写入顺序读取
try (DataInputStream dis = new DataInputStream(
new BufferedInputStream(new FileInputStream(filename)))) {
int intVal = dis.readInt();
double doubleVal = dis.readDouble();
boolean boolVal = dis.readBoolean();
String strVal = dis.readUTF();
System.out.println("DataInputStream 读取:");
System.out.println(" int: " + intVal);
System.out.println(" double: " + doubleVal);
System.out.println(" boolean: " + boolVal);
System.out.println(" String: " + strVal);
}
// 清理
new File(filename).delete();
}
/**
* ============================================================
* 6. 对象流（序列化）
* ============================================================
*/
public static void objectStreams() throws IOException {
System.out.println("\n" + "=".repeat(60));
System.out.println("6. 对象流（序列化）");
System.out.println("=".repeat(60));
System.out.println("""
对象序列化：
- 将对象转换为字节流
- 类必须实现 Serializable 接口
- transient 字段不会被序列化
- serialVersionUID 用于版本控制
""");
String filename = "object_test.ser";
// 【写入对象】
try (ObjectOutputStream oos = new ObjectOutputStream(
new FileOutputStream(filename))) {
Person person = new Person("张三", 25);
oos.writeObject(person);
// 可以写入多个对象
oos.writeObject(new Person("李四", 30));
System.out.println("对象序列化完成");
}
// 【读取对象】
try (ObjectInputStream ois = new ObjectInputStream(
new FileInputStream(filename))) {
Person p1 = (Person) ois.readObject();
Person p2 = (Person) ois.readObject();
System.out.println("对象反序列化:");
System.out.println(" " + p1);
System.out.println(" " + p2);
} catch (ClassNotFoundException e) {
System.out.println("类未找到: " + e.getMessage());
}
// 清理
new File(filename).delete();
}
/**
* ============================================================
* 7. 压缩流
* ============================================================
*/
public static void compressionStreams() throws IOException {
System.out.println("\n" + "=".repeat(60));
System.out.println("7. 压缩流");
System.out.println("=".repeat(60));
// 【GZIP 压缩】
System.out.println("--- GZIP 压缩 ---");
String original = "这是一段需要压缩的文本。".repeat(100);
String gzipFile = "test.gz";
// 压缩
try (GZIPOutputStream gzos = new GZIPOutputStream(
new FileOutputStream(gzipFile))) {
gzos.write(original.getBytes(StandardCharsets.UTF_8));
}
System.out.println("原始大小: " + original.getBytes().length + " bytes");
System.out.println("压缩后: " + new File(gzipFile).length() + " bytes");
// 解压
try (GZIPInputStream gzis = new GZIPInputStream(
new FileInputStream(gzipFile))) {
byte[] buffer = gzis.readAllBytes();
String decompressed = new String(buffer, StandardCharsets.UTF_8);
System.out.println("解压成功: " + (original.equals(decompressed)));
}
// 【ZIP 压缩多个文件】
System.out.println("\n--- ZIP 压缩 ---");
String zipFile = "test.zip";
try (ZipOutputStream zos = new ZipOutputStream(
new FileOutputStream(zipFile))) {
// 添加第一个文件
zos.putNextEntry(new ZipEntry("file1.txt"));
zos.write("文件1的内容".getBytes(StandardCharsets.UTF_8));
zos.closeEntry();
// 添加第二个文件
zos.putNextEntry(new ZipEntry("folder/file2.txt"));
zos.write("文件2的内容".getBytes(StandardCharsets.UTF_8));
zos.closeEntry();
System.out.println("ZIP 压缩完成");
}
// 解压 ZIP
try (ZipInputStream zis = new ZipInputStream(
new FileInputStream(zipFile))) {
ZipEntry entry;
System.out.println("ZIP 内容:");
while ((entry = zis.getNextEntry()) != null) {
System.out.println(" " + entry.getName() + " (" + entry.getSize() + " bytes)");
zis.closeEntry();
}
}
// 清理
new File(gzipFile).delete();
new File(zipFile).delete();
}
}
/**
* 可序列化的 Person 类
*/
class Person implements Serializable {
private static final long serialVersionUID = 1L;
private String name;
private int age;
private transient String password; // 不会被序列化
public Person(String name, int age) {
this.name = name;
this.age = age;
this.password = "secret";
}
@Override
public String toString() {
return "Person{name='" + name + "', age=" + age +
", password=" + password + "}";
}
}
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