Java之IO

1.流

概念：内存与存储设备间传输数据的通道

分类： 按方向：输入（存储设备->内存），输出（内存->存储设备） 按单位：字节流（字节为单位，可读所有），字符流（字符为单位，只读文本） 按功能：节点流（读写功能），过滤流（节点流上增加功能）

2.字节流

文件字节流

FileInputStream和FileOutputStream是InputStream和OutputStream的子类。

单字节读取

public static void main(String[] args) throws IOException { FileInputStream fis = new FileInputStream("D:\\hehe.txt"); int data = 0; while ((data = fis.read() )!= -1){ System.out.print((char)data); } fis.close(); }

一次性读取多个字节

public static void main(String[] args) throws IOException { FileInputStream fis = new FileInputStream("D:\\hehe.txt"); byte[] buf = new byte[1024]; int count = fis.read(buf); System.out.println(new String(buf)); System.out.println(count); fis.close(); }

一次性写入一个字符串

public static void main(String[] args) throws IOException { FileOutputStream fos = new FileOutputStream("D:\\test\\bbb.txt"); String word = "helloworld"; fos.write(word.getBytes()); fos.close(); }

文件的复制

public static void main(String[] args) throws IOException { FileInputStream fis = new FileInputStream("D:\\test\\bbb.txt"); FileOutputStream fos = new FileOutputStream("D:\\test\\aaa.txt"); byte[] buf = new byte[1024]; int count = 0; while ((count = fis.read(buf)) != -1){ fos.write(buf,0,count); } fis.close(); fos.close(); }

BufferedInputStream

public static void main(String[] args) throws IOException { FileInputStream fis = new FileInputStream("D:\\test\\aaa.txt"); BufferedInputStream bis = new BufferedInputStream(fis); for (int data = 0;data != -1;data = bis.read()){ System.out.print((char)data); } bis.close(); }

BufferedOutputStream

public static void main(String[] args) throws Exception{ FileOutputStream fos = new FileOutputStream("D:\\test\\ccc.txt"); BufferedOutputStream bos = new BufferedOutputStream(fos); for (int i = 0; i < 10; i++) { bos.write("helloworld".getBytes()); bos.flush(); } bos.close(); }

序列化和反序列化

Java序列化是把 对象 转换为 字节序列 的过程,用ObjectOutputStream实现 Java反序列化是把 字节序列 恢复为 对象过程，用,用ObjectInputStream实现

要求：序列化的类必须实现Serializable接口。

public static void main(String[] args) throws Exception { FileOutputStream fos = new FileOutputStream("d:\\test\\stu.bin"); ObjectOutputStream oos = new ObjectOutputStream(fos); Student student = new Student("张三",20); oos.writeObject(student); oos.close(); System.out.println("完成"); }

反序列化

public static void main(String[] args) throws Exception { FileInputStream fis = new FileInputStream("d:\\test\\stu.bin"); ObjectInputStream ois = new ObjectInputStream(fis); Student student =(Student) ois.readObject(); ois.close(); }

序列化版本ID：保证序列化和反序列化的类是同一个类 使用transient修饰的属性，不能被序列化 ’序列化多个对象，用集合实现

乱码出现的原因：编码和解码的方式不一样

3.字符流

字节流遇到的问题：读3个汉字，12字节，字节流一个字节一个字节读导致乱码 单个字符读取

public static void main(String[] args) throws Exception { FileReader fr = new FileReader("D:\\test\\ccc.txt"); int data = 0; while ((data=fr.read()) != -1){ System.out.print((char) data); } }

字符数组读取

public static void main(String[] args) throws Exception { FileReader fr = new FileReader("D:\\test\\ccc.txt"); char[] buf = new char[1024]; int count = 0; while ((count=fr.read(buf)) != -1){ System.out.print(new String(buf,0,count)); } }

字符流的写

public static void main(String[] args) throws Exception{ FileWriter fw = new FileWriter("D:\\test\\dd.txt"); for (int i = 0; i < 10; i++) { fw.write("java是最好语言\n"); } fw.close(); }

字符流复制

public void charCopy() throws Exception{ FileReader fr = new FileReader("D:\\test\\dd.txt"); FileWriter fw = new FileWriter("D:\\test\\ddd.txt"); int data = 0; while ((data = fr.read()) != -1){ fw.write(data); fw.flush(); } fr.close(); fw.close(); } @Test public void BufferedReaderTest() throws Exception{ FileReader reader = new FileReader("D:\\test\\dd.txt"); BufferedReader br = new BufferedReader(reader); char[] buf = new char[1024]; int count; while ((count = br.read(buf)) != -1){ System.out.println(new String(buf,0,count)); } br.close(); } @Test public void BufferedReaderTest2() throws Exception{ FileReader reader = new FileReader("D:\\test\\dd.txt"); BufferedReader br = new BufferedReader(reader); String line = null; while ((line = br.readLine())!= null){ System.out.println(line); } br.close(); } @Test public void BufferedWriter() throws Exception{ FileWriter fileWriter = new FileWriter("D:\\test\\write.txt"); BufferedWriter bw = new BufferedWriter(fileWriter); bw.write("我凑"); bw.close(); } /** * 打印流 * @throws Exception */ @Test public void printWriter() throws Exception{ PrintWriter pw = new PrintWriter("D:\\test\\pw.txt"); pw.println("true"); pw.println(123); pw.close(); } /** *转换流，硬盘上的字节流和内存的字符流之间的转换 * 可设置编码格式 */ @Test public void InputStreamReader() throws Exception{ FileInputStream fis = new FileInputStream("D:\\test\\dd.txt"); InputStreamReader isr = new InputStreamReader(fis,"UTF-8"); int data = 0; while ((data = isr.read())!= -1){ System.out.print((char) data); } isr.close(); } @Test public void OutputStreamWriter() throws Exception{ FileOutputStream fos = new FileOutputStream("D:\\test\\tt.txt"); OutputStreamWriter osw = new OutputStreamWriter(fos,"UTF-8"); osw.write("qqqqqq吾问无为谓吾问无为谓"); osw.close(); }

文件的操作

import org.junit.Test; import java.io.File; import java.io.FileFilter; import java.io.IOException; import java.util.Date; public class FileTest { @Test public void FileOpe() throws Exception { File file = new File("D:\\test\\fileeeee.txt"); //System.out.println(file.toString()); if (!file.exists()){ file.createNewFile(); } System.out.println(file.getAbsolutePath()); System.out.println(file.getName()); System.out.println(file.getParent()); System.out.println(new Date(file.lastModified()).toLocaleString()); System.out.println(file.isFile()); //file.delete(); } @Test public void DirOpe() throws Exception { File dir = new File("D:\\test"); if (!dir.exists()){ dir.mkdirs(); } //dir.delete(); System.out.println(dir.isDirectory()); String[] list = dir.list(); // for (String s:list // ) { // System.out.println(s); // } File[] jpgs = dir.listFiles(new FileFilter() { @Override public boolean accept(File pathname) { if (pathname.getName().endsWith("txt")) { return true; } else { return false; } } }); for (File f: jpgs ) { System.out.println(f.getName()); } } @Test public void listDirRun(){ File dir = new File("D:\\test1"); delDir(dir); } public void listDir(File dir){ File[] files = dir.listFiles(); if (files!=null&&files.length>0){ for (File f:files ) { if (f.isDirectory()){ listDir(f); } else { System.out.println(f.getAbsolutePath()); } } } } public void delDir(File dir){ File[] files = dir.listFiles(); if (files!=null&&files.length>0) { for (File f : files ) { if (f.isDirectory()) { delDir(f); } else { System.out.println(f.getAbsolutePath()+"删除"); f.delete(); } } } System.out.println(dir.getAbsolutePath()+"删除"); dir.delete(); } } properties @Test public void propertiesTest() throws Exception { Properties properties = new Properties(); properties.setProperty("username","张三"); properties.setProperty("age","20"); Set<String> pronames = properties.stringPropertyNames(); for (String s:pronames ) { System.out.println(s + properties.getProperty(s)); } // PrintWriter pw = new PrintWriter("D:\\test\\pro.txt"); // properties.list(pw); // pw.close(); // FileOutputStream fos = new FileOutputStream("D:\\test\\store.properties"); // properties.store(fos,"comments"); // fos.close(); Properties properties2 = new Properties(); FileInputStream fis = new FileInputStream("D:\\test\\store.properties"); properties2.load(fis); System.out.println(properties2); }