Java 文件读写操作

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1. 对于文本文件的读写

1.1. 读取文本文件

package com.martinwangjun.io;import java.io.FileReader;import java.io.IOException;public class FileReaderTest {    // 注意，需要抛出IOException或在代码中使用try...catch...    public static void main(String[] args) throws IOException     {        // 对于eclipse，注意实际的路径，我们这里用了package        FileReader fileReader = new FileReader(            "./src/com/martinwangjun/io/FileReaderTest.java");        char[] buffer = new char[1024];        int hasReader = 0;        while ((hasReader = fileReader.read(buffer)) > 0) {            System.out.println(new String(buffer, 0, hasReader));        }        // 这里其实写得不严谨，最好使用Java 7的AutoClosable        // 或者finally中关闭资源        fileReader.close();    }}

1.2. 写入文本文件

package com.martinwangjun.io;import java.io.FileWriter;public class FileWriterTest {    public static void main(String[] args) {        // 这里用来Java 7的AutoClosable的特性，会自动关闭资源。        try(FileWriter fileWriter = new FileWriter(                "src/com/martinwangjun/io/poem.txt")) {            fileWriter.write("先令\r\n");        } catch (Exception ex) {            ex.printStackTrace();        }    }}

2. 二进制文件

package com.martinwangjun.io;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;public class FileOutputStreamTest {    public static void main(String[] args) throws IOException{        // 使用了Java 7的自动关闭机制        try(FileInputStream fileInputStream = new FileInputStream(                "src/com/martinwangjun/io/01.jpg");            FileOutputStream fileOutputStream = new FileOutputStream(                "src/com/martinwangjun/io/02.jpg");                ){            byte[] buffer = new byte[1024];            int hasRead = 0;            while ((hasRead = fileInputStream.read(buffer)) > 0) {                fileOutputStream.write(buffer, 0, hasRead);            }            buffer = "Powered By Martin".getBytes();            fileOutputStream.write(buffer, 0,                 "Powered By Martin".length());        }        catch (Exception ex) {            ex.printStackTrace();        }    }}

3. 利用包装流

3.1. 利用PrintStream流来包装FileOutputStream

package com.martinwangjun.io;import java.io.FileOutputStream;import java.io.IOException;import java.io.PrintStream;public class PrintStreamTest {    public static void main(String[] args) throws IOException {        try(            FileOutputStream fos = new FileOutputStream(                    "src/com/martinwangjun/io/test.txt");            PrintStream ps = new PrintStream(fos))        {            // 这样的话不用考虑怎么写入文件，当成普通的打印一样使用            ps.println("普通字符串");            ps.println(new PrintStreamTest());        }        catch (Exception ex) {            ex.printStackTrace();        }    }}

4. 获取用户输入

package com.martinwangjun.io;import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;public class KeyinTest {    public static void main(String[] args) throws IOException{        InputStreamReader reader = null;        BufferedReader bufferedReader = null;        try {            reader = new InputStreamReader(System.in);            bufferedReader = new BufferedReader(reader);            String line = null;            while ((line = bufferedReader.readLine()) != null) {                if(line.toLowerCase().equals("exit")){                    System.exit(1);                }                System.out.println(line);            }        } catch (Exception ex) {            ex.printStackTrace();        } finally {            if(reader != null){                try {                    reader.close();                } catch (Exception ex) {                    ex.printStackTrace();                }            }            if(bufferedReader != null){                try {                    bufferedReader.close();                } catch (Exception ex) {                    ex.printStackTrace();                }            }        }    }}

5. 添加而不是覆盖

package com.martinwangjun.io;import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.FileOutputStream;import java.io.InputStreamReader;import java.io.OutputStreamWriter;public class BufferedWriteTextFile {    public static void main(String[] args) throws Exception {        try (            // 这里用了true，表示可以Append            BufferedWriter bufferedWriter = new BufferedWriter(                new OutputStreamWriter(                    new FileOutputStream(                        "src/com/martinwangjun/io/output.txt", true)));            BufferedReader bufferedReader = new BufferedReader(                new InputStreamReader(System.in)))         {            String line = null;            while( ! (line = bufferedReader.readLine()).equals("")){                bufferedWriter.write(line);                bufferedWriter.newLine();            }        } catch (Exception e) {            e.printStackTrace();        }    }}

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