给出几个Java I/O 操作的示例代码。
创建文件或目录
import java.io.File; import java.io.IOException; public class TestFileIO { public static void main(String[] args) { File dir = new File("dir1"); dir.mkdir(); //创建目录 File file = new File(dir,"file1"); //目录加文件名 File file2 = new File("dir1/file2"); //完整路径 try { file.createNewFile(); //创建文件,若存在同名文件,不会覆盖 file2.createNewFile(); } catch (IOException e) { e.printStackTrace(); } } } |
删除文件
import java.io.File; public class TestFileIO { public static void main(String[] args) { File file = new File("dir1/file2"); if (file.delete()){ System.out.println(file.getName() + " is deleted!"); }else { System.out.println("File is not deleted!"); } } } |
向文件逐行写入内容(覆盖写）
FileOutputStream
import java.io.*;
public class TestFileIO {
public static void main(String[] args) throws IOException {
File fout = new File("dir1/file1");
FileOutputStream fos = new FileOutputStream(fout);
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(fos));
for (int i = 0; i < 10; i++){
bw.write("something");
bw.newLine();
}
bw.close();
}
}
FileWriter
import java.io.*;
public class TestFileIO {
public static void main(String[] args) throws IOException {
File fout = new File("dir1/file1");
FileWriter fw = new FileWriter(fout);
for (int i = 0; i < 10; i++){
fw.write("something" + System.getProperty("line.separator"));
}
fw.close();
}
}
PrintWriter
import java.io.*;
public class TestFileIO {
public static void main(String[] args) throws IOException {
File fout = new File("dir1/file1");
PrintWriter pw = new PrintWriter(new FileWriter(fout));
for (int i = 0; i < 10; i++){
pw.println("something");
}
pw.close();
}
}
OutputStreamWriter
import java.io.*;
public class TestFileIO {
public static void main(String[] args) throws IOException {
File fout = new File("dir1/file1");
FileOutputStream fos = new FileOutputStream(fout);
OutputStreamWriter osw = new OutputStreamWriter(fos);
for (int i = 0; i < 10; i++) {
osw.write("something" + System.getProperty("line.separator"));
}
osw.close();
}
}
注：
往文本文件里写内容用FileWriter即可，比较方便。但是如果要自己定义字符编号和byte-buffer大小的话就要用FileOutputStream。
PrintWriter跟FileWriter的主要区别是PrintWriter可以格式化输出。该类实现了PrintStream的所有print方法。
追加写
import java.io.*; public class TestFileIO { public static void main(String[] args) throws IOException { File fout = new File("dir1/file1"); FileOutputStream fos = new FileOutputStream(fout,true); //跟覆盖写唯一的区别是这里加了个true参数。 OutputStreamWriter osw = new OutputStreamWriter(fos); for (int i = 0; i < 10; i++) { osw.write("something" + System.getProperty("line.separator")); } osw.close(); } } |
拷贝文件
import java.io.*; import java.nio.file.Files; import java.nio.file.Path; import java.nio.file.Paths; public class TestFileIO { public static void main(String[] args) throws IOException { Path sour = Paths.get("dir1/file1"); Path des = Paths.get("dir1/file2"); Files.copy(sour,des); //Files.copy(a,b)。 } } |
合并多个文件
读取多个文件的内容，写入一个文件。
import java.io.*; /** * Created by lbd on 2017/1/13. */ public class MergeFiles { public static void main(String[] args) throws IOException { String sourceFile1Path = "dir1/file1"; String sourceFile2Path = "dir1/file2"; String mergedFilePath = "dir1/mergedFile.txt"; File[] files = new File[2]; files[0] = new File(sourceFile1Path); files[1] = new File(sourceFile2Path); File mergedFile = new File(mergedFilePath); mergeFiles(files,mergedFile); } public static void mergeFiles(File[] files,File mergedFile) throws IOException { FileWriter fw = new FileWriter(mergedFile,true); BufferedWriter bw = new BufferedWriter(fw); for (File f : files){ System.out.println("merging: " + f.getName()); FileReader fr = new FileReader(f); BufferedReader br = new BufferedReader(fr); String aLine; while ((aLine = br.readLine()) != null){ bw.write(aLine); bw.newLine(); } br.close(); } bw.close(); } } |
移动文件
调用的是File.renameTo()方法。
import java.io.*; public class MoveFile { public static void main(String[] args) throws IOException { File f1 = new File("dir1/file1"); File f2 = new File("dir1/dir2/file3"); //dir2目录必须存在,否则无法移动成功 f1.renameTo(f2); } } |
对文件内容排序
file1内容如下：
dog cat --windows --kankan pps game --annot be guaranteed as it is, generally speaking, --impossible to make any hard gu arantees in the p --resence of unsynchr |
对行进行排序，以上面的文本为例，排序后arantees in the p应该在第一行
import java.io.*; import java.util.ArrayList; import java.util.Collections; /** * Created by lbd on 2017/1/13. */ public class TestJavaIO { public static void main(String[] args) throws IOException { File fin = new File("file1"); File fout = new File("file2"); String s; FileWriter fw = new FileWriter(fout); FileReader fr = new FileReader(fin); BufferedReader br = new BufferedReader(fr); BufferedWriter bw = new BufferedWriter(fw); ArrayList<String> al = new ArrayList<>(); while ((s = br.readLine()) != null ){ if (!s.trim().startsWith("-") && s.trim().length() > 0){ al.add(s); } } Collections.sort(al); for (String line : al){ bw.write(line); bw.newLine(); bw.write("------------------------------"); bw.newLine(); } br.close(); bw.close(); } } |
file2内容如下：
arantees in the p ------------------------------ as it is, generally speaking, ------------------------------ cat ------------------------------ dog ------------------------------ game ------------------------------ pps ------------------------------ |
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