第17 章 : IO操作深入
80 字符编码
常用的编码
1、GBK/GB2312 国标编码, GB2312简体中文,GBK包含简体和繁体
2、ISO8859-1 国际通用编码,描述所有字母
3、UNICODE 16进制存储,描述所有问题
4、UTF 象形文字部分使用16进制,普通字母采用ISO8859-1,主要使用UTF-8
列出本机属性
System.getProperties().list(System.out);
项目中出现乱码问题就是编码和解码标准不统一
81 内存操作流
文件操作流 以文件为操作终端,InputStream、OutputStream
内存操作流
1、字节内存操作流 ByteArrayOutputStream ByteArrayInputStream
2、字符内存操作流 CharArrayWriter CharArrayReader
继承关系
OutputStream
-FileOutputStream
-ByteArrayOutputStream
InputStream
-FileInputStream
-ByteArrayInputStream
Writer
-OutputStreamWriter
-FileWriter
-CharArrayWriter
Reader
-InputStreamReader
-FileReader
-CharArrayReader
示例:利用内存流小写转大写操作
import java.io.*;
class Demo{
public static void main(String[] args) throws IOException {
String message = "hello java";
// 将数据保存到内存流中
InputStream input = new ByteArrayInputStream(message.getBytes());
OutputStream output = new ByteArrayOutputStream();
int data = 0;
// 每次读取一个数据
while ((data = input.read())!=-1){
output.write(Character.toUpperCase(data));
}
System.out.println(output);
// HELLO JAVA
output.close();
input.close();
}
}
82 管道流
发送信息 <- 管道 -> 接收信息
字节管道流 PipedInputStream, PipedOutputStream
字符管道流 PipedReader, PipedWriter
继承关系
InputStream
-PipedInputStream
OutputStream
-PipedOutputStream
Reader
-PipedReader
Writer
-PipedWriter
管道发送接收数据
import java.io.*;
class Sender implements Runnable {
private PipedOutputStream output;
public Sender() {
this.output = new PipedOutputStream();
}
@Override
public void run() {
try {
this.output.write("你好".getBytes());
} catch (IOException e) {
e.printStackTrace();
}
try {
this.output.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public PipedOutputStream getOutput() {
return this.output;
}
}
class Receiver implements Runnable {
private PipedInputStream input;
public Receiver() {
this.input = new PipedInputStream();
}
@Override
public void run() {
try {
byte[] data = new byte[1024];
int len = this.input.read(data);
System.out.println(new String(data, 0, len));
// 你好
} catch (IOException e) {
e.printStackTrace();
}
try {
this.input.close();
} catch (IOException e) {
e.printStackTrace();
}
}
public PipedInputStream getInput() {
return this.input;
}
}
class Demo {
public static void main(String[] args) throws IOException {
Sender sender = new Sender();
Receiver receiver = new Receiver();
// 管道连接
sender.getOutput().connect(receiver.getInput());
new Thread(sender).start();
new Thread(receiver).start();
}
}
83 RandomAccessFile
随机读取类,可以移动文件指针
public RandomAccessFile(String name, String mode)
import java.io.*;
class Demo {
public static void main(String[] args) throws IOException {
// 写入
RandomAccessFile writer = new RandomAccessFile("demo.txt", "rw");
writer.write("你好世界".getBytes());
writer.close();
// 读取
RandomAccessFile reader = new RandomAccessFile("demo.txt", "rw");
String line;
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
writer.close();
}
}
第18 章 : 输入与输出支持
84 打印流
设计思想:装饰设计模式
为OutputStream 类实现一层包装
PrintStream
PrintWriter
继承关系
OutputStream
-FilterOutputStream
-PrintStream
Writer
-PrintWriter
import java.io.*;
class Demo {
public static void main(String[] args) throws IOException {
PrintWriter writer = new PrintWriter(new FileWriter("demo.txt"));
// 换行输出
writer.println("你好");
// 格式化输出
writer.printf("姓名 %s, 年龄: %s", "小强", 23);
writer.close();
}
}
只要是文件内容输出时都使用打印流
85 System类对IO的支持
System是系统类
1、标准输出(显示器)
2、错误输出
3、标准输入(键盘)
public final class System {
public final static InputStream in = null;
public final static PrintStream out = null; // 黑色字体
public final static PrintStream err = null; // 红色字体
}
修改输出位置
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintStream;
class Demo {
public static void main(String[] args) throws IOException {
System.setErr(new PrintStream(new FileOutputStream(new File("demo.txt"))));
System.err.println("你好");
}
}
接收键盘输入(一般不用此方法)
import java.io.IOException;
import java.io.InputStream;
class Demo {
public static void main(String[] args) throws IOException {
InputStream input = System.in;
System.out.println("请输入姓名:");
byte[] data = new byte[1024];
int len = input.read(data);
System.err.println(new String(data, 0, len));
}
}
86 BufferedReader缓冲输入流
JDK < 1.5
缓冲字符输入流
继承关系
Reader
-BufferedReader
代码示例
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
class Demo {
public static void main(String[] args) throws IOException {
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
System.out.println("请输入:");
String msg = reader.readLine();
System.out.println(msg);
}
}
87 Scanner扫描流
JDK > 1.5
替代BufferedReader
构造函数
判断是否有数据 public boolean hasNext()
读取数据 public String next()
设置分隔符
import java.io.IOException;
import java.util.Scanner;
class Demo {
public static void main(String[] args) throws IOException {
Scanner scanner = new Scanner(System.in);
System.out.println("请输入年龄:");
if(scanner.hasNextInt()){
int age = scanner.nextInt();
System.out.println("您输入的年龄是:" + age);
} else{
System.out.println("输入不正确");
}
scanner.close();
}
}
可以结合正则进行判断验证
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Scanner;
class Demo {
public static void main(String[] args) throws ParseException {
Scanner scanner = new Scanner(System.in);
System.out.println("请输入生日:");
if (scanner.hasNext("\\d{4}-\\d{2}-\\d{2}")) {
String msg = scanner.next("\\d{4}-\\d{2}-\\d{2}");
System.out.println("您输入的年龄是:" + new SimpleDateFormat("yyyy-MM-dd").parse(msg));
} else {
System.out.println("输入不正确");
}
scanner.close();
}
}
读取文件
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
class Demo {
public static void main(String[] args) throws FileNotFoundException {
Scanner scanner = new Scanner(new File("demo.txt"));
// 设置换行分隔符
// scanner.useDelimiter("\n");
while (scanner.hasNext()) {
System.out.println(scanner.next());
}
scanner.close();
}
}
开发中:
输出使用PrintWriter打印流
输入使用Scanner扫描流
第19 章 : 对象序列化
88 对象序列化基本概念
对象序列化:
将内存中保存的对象以二进制数据的形式处理,
实现对象的保存或者网络传输
保存到文件
堆内存 - 二进制转换 -> 保存到数据库
发送到服务器
要序列化的对象必须实现java.io.Serializable 接口
没有任何方法,只是描述一种能力
示例
import java.io.Serializable;
class Person implements Serializable {
private String name;
private int age;
public Person(String name, int age) {
= name;
this.age = age;
}
}
89 序列化与反序列化处理
继承关系
InputStream(ObjectInput, ObjectStreamConstants)
-ObjectInputStream
OutputStream(ObjectOutput, ObjectStreamConstants)
-ObjectOutputStream
代码示例
import java.io.*;
class Person implements Serializable {
private String name;
private int age;
public Person(String name, int age) {
= name;
this.age = age;
}
}
class Demo {
private static final File SAVE_FILE = new File("demo.person");
public static void main(String[] args) throws IOException, ClassNotFoundException {
Person person = new Person("Tom", 23);
// saveObject(person);
System.out.println(loadObject());
// Person@15aeb7ab
}
// 序列化
public static void saveObject(Object obj) throws IOException {
ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(SAVE_FILE));
oos.writeObject(obj);
oos.close();
}
// 反序列化
public static Object loadObject() throws IOException, ClassNotFoundException {
ObjectInputStream ois = new ObjectInputStream(new FileInputStream(SAVE_FILE));
Object obj = ois.readObject();
ois.close();
return obj;
}
}
实际开发中不直接操作ObjectInputStream、ObjectOutputStream
90 transient关键字
表示进行序列化处理时,不处理被transient关键字修饰的字段
不常用,知道即可
IO继承体系整合
// 字节流:
OutputStream(Closeable, Flushable)
-FileOutputStream
-ByteArrayOutputStream
-PipedOutputStream
-FilterOutputStream
-PrintStream
-ObjectOutputStream
InputStream(Closeable)
-FileInputStream
-ByteArrayInputStream
-PipedInputStream
-ObjectInputStream
// 字符流:
Writer(Appendable, Closeable, Flushable)
-OutputStreamWriter
-FileWriter
-CharArrayWriter
-PipedReader
-PrintWriter
-BufferedWriter
Reader(Readable, Closeable)
-InputStreamReader
-FileReader
-CharArrayReader
-PipedWriter
-BufferedReader