如何使用 Java 从文本文档中提取内容？
java 中有几种读取文本文件的方式，如 BufferReader 、 FileReader 和 Scanner 。每种方法都提供了一种读取文本文件的独特方式。
方法:
- 使用文件类
- 使用文件阅读器类
- 使用 BufferReader 类
- 使用扫描仪类
让我们通过一个例子来详细了解每一个方法，以便更好地理解这些方法，从而在以后实现相同的方法来从文本文档中提取内容。
方法 1: 使用文件类
正如 Java 提供的*Java . nio . file。* API 我们可以使用Java . nio . file . files*类将一个文件的所有内容读入一个数组。要读取文本文件，我们可以使用文件类的ReadalBytes()方法 ，当您需要内存中的所有文件内容以及处理小文件时，使用该方法。*
**示例:****
*Java 语言(一种计算机语言，尤用于创建网站)*
**// Java Program to Extract Content From a Text Document
// Using Files class
// Importing java.nio package for network linking
import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
// Importing List class from java.util package
import java.util.List;
// Main class
public class GFG {
// Method 1
// To read the file using class
private static void readUsingClass(String fileName)
throws IOException
{
// Creating an object of Path class
Path path = Paths.get(fileName);
// To read file to byte array
byte[] bytes = Files.readAllBytes(path);
// Display message only
System.out.println(
"Read text file using Files class");
// Reading the file to String List
@SuppressWarnings("unused")
// Creating a List class object of string type
// as data in file to be read is words
List<String> allLines = Files.readAllLines(
path, StandardCharsets.UTF_8);
System.out.println(new String(bytes));
}
// Method 2
// Main driver method
public static void main(String[] args)
throws IOException
{
// Custom input directory passed where text
String fileName
= "/Users/mayanksolanki/Desktop/file.txt";
// read using FileReader, no encoding support, not
// efficient
readUsingClass(fileName);
}
}**
**输出:****
*
*
**方法二: 使用文件阅读器类T5】****
*我们可以使用 *java.io.FileReader 可以用来从文件中读取数据(以字符为单位)。这是一种非常有效的逐行读取文件的方法。****
**语法:****
**FileReader input = new FileReader(String name);**
**示例:****
*Java 语言(一种计算机语言，尤用于创建网站)*
**// Java Program to Extract Content From a Text Document
// Using FileReader class
// Importing required libraries
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
// Main class
public class GFG {
// Method
// To read the file using File Reader
private static void readUsingFileReader(String fileName)
throws IOException
{
File file = new File(fileName);
FileReader fr = new FileReader(file);
BufferedReader br = new BufferedReader(fr);
String line;
System.out.println(
"Reading text file using FileReader");
while ((line = br.readLine()) != null) {
// process the line
System.out.println(line);
}
br.close();
fr.close();
}
// Method 2
// Main driver method
public static void main(String[] args)
throws IOException
{
String fileName
= "/Users/mayanksolanki/Desktop/file.txt";
// read using FileReader, no encoding support, not
// efficient
readUsingFileReader(fileName);
}
}**
**输出:****
*
*
**方法三: 使用 级****
*如果你想逐行读取文件，如果你想处理该文件，那么你必须使用 BufferedReader。它也用于处理大文件，也支持编码。BufferReader 上的读取操作非常高效。*
**注意:要么指定缓冲区的大小，要么保持缓冲区的默认大小为 8KB。****
**语法:****
**BufferedReader in = new BufferedReader(Reader in, int size);**
**实施:****
**Hello I am learning web- development.
I am writing article for GFG.
I am cloud enthusiast.
I am an open-source contributor.**
**注意:开始之前，使用创建一个文本文件。txt 扩展名，并在练习时随时使用该文件的路径。****
**示例:****
*Java 语言(一种计算机语言，尤用于创建网站)*
**// Java Program to Extract Content From a Text Document
// Using BufferedReader class
// Importing required libraries
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
// Main class
public class GFG {
// Method
// To read the file using Buffered Reader
private static void
readUsingBufferedReader(String fileName)
throws IOException
{
File file = new File(fileName);
FileReader fr = new FileReader(file);
// read file line by line
BufferedReader br = new BufferedReader(fr);
String line;
System.out.println(
"Read text file using BufferedReader");
while ((line = br.readLine()) != null) {
// process the line
System.out.println(line);
}
// close resources
br.close();
fr.close();
}
// Method 2
// Main driver method
public static void main(String[] args)
throws IOException
{
String fileName
= "/Users/mayanksolanki/Desktop/file.txt";
// read using FileReader, no encoding support, not
// efficient
readUsingBufferedReader(fileName);
}
}**
**输出:****
*
*
**方法 4: 使用扫描仪类****
*如果我们想基于某个表达式阅读文档&如果你想逐行阅读文档，那么我们使用 Scanner 类。扫描仪将输入分成标记，默认情况下，标记与空格匹配。*
**示例:****
*Java 语言(一种计算机语言，尤用于创建网站)*
**// Java Program to Extract Content From a Text Document
// Using Scanner class
// Importing required libraries
import java.io.IOException;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Scanner;
// Main class
public class GFG {
// Method 1
// To read the file using Scanner
private static void readUsingScanner(String fileName)
throws IOException
{
// Again, creating Path class object in main()
// method
Path path = Paths.get(fileName);
// Creating Scanner class object to take input
Scanner scanner = new Scanner(path);
// Display message for readability
System.out.println("Read text file using Scanner");
// Now reading file line by line
// using hasNextLine() method
while (scanner.hasNextLine()) {
// Processing each line
String line = scanner.nextLine();
// Printing processed lines
System.out.println(line);
}
// close() method is used to close all the read
// write connections
scanner.close();
}
// Method 2
// Main driver method
public static void main(String[] args)
throws IOException
{
// Custom input text document
// present already on the machine
String fileName
= "/Users/mayanksolanki/Desktop/file.txt";
// Now lastly reading using FileReader
// no encoding support, not efficient
readUsingScanner(fileName);
}
}**
**输出:****
*
*
**实施:****
*这里的“*my _ file . txt”是一个演示文件，用于下面演示的程序，其中示例行如下:****
**Hello I am learning web- development.
I am writing article of GFG.
I am cloud enthusiast.
I am an open-source contributor.**
**例 1:****
*Java 语言(一种计算机语言，尤用于创建网站)*
**// Java Program to Implement Extraction of Content
// From a Text Document
// Importing required libraries
import java.io.BufferedReader;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import java.util.Scanner;
// Main class
public class read_file {
// Method 1
// To read the file using File Reader
private static void readUsingFileReader(String fileName)
throws IOException
{
File file = new File(fileName);
FileReader fr = new FileReader(file);
BufferedReader br = new BufferedReader(fr);
String line;
System.out.println(
"Reading text file using FileReader");
while ((line = br.readLine()) != null) {
// process the line
System.out.println(line);
}
br.close();
fr.close();
}
// Method 2
// To read the file using Buffered Reader
private static void
readUsingBufferedReader(String fileName)
throws IOException
{
File file = new File(fileName);
FileReader fr = new FileReader(file);
// read file line by line
BufferedReader br = new BufferedReader(fr);
String line;
System.out.println(
"Read text file using BufferedReader");
while ((line = br.readLine()) != null) {
// process the line
System.out.println(line);
}
// Closing resources to
// release memory spaces
br.close();
fr.close();
}
// Method 3
// To read the file using Scanner
private static void readUsingScanner(String fileName)
throws IOException
{
Path path = Paths.get(fileName);
Scanner scanner = new Scanner(path);
System.out.println("Read text file using Scanner");
// read line by line
while (scanner.hasNextLine()) {
// process each line
String line = scanner.nextLine();
System.out.println(line);
}
scanner.close();
}
// Method 4
// To read the file using class
private static void readUsingClass(String fileName)
throws IOException
{
Path path = Paths.get(fileName);
// read file to byte array
byte[] bytes = Files.readAllBytes(path);
System.out.println(
"Read text file using Files class");
// read file to String list
@SuppressWarnings("unused")
List<String> allLines = Files.readAllLines(
path, StandardCharsets.UTF_8);
System.out.println(new String(bytes));
}
// Method 5
// main driver method
public static void main(String[] args)
throws IOException
{
String fileName
= "C:\\Users\\HP\\Desktop\\my_file.txt";
// using Java 7 Files class to
// process small files, get complete file data
readUsingClass(fileName);
// using Scanner class for
// large files, to read line by line
readUsingScanner(fileName);
// read using BufferedReader, to read line by line
readUsingBufferedReader(fileName);
// read using FileReader, no encoding support, not
// efficient
readUsingFileReader(fileName);
}
}**
**示例 2: 从文本文件中读取特定行****
*现在，如果您想从给定的文档中读取特定的行，那么我们使用 BufferReader 方法。根据文件的不同，使用了 BufferReader()方法，这样我们的代码可以更快更有效地工作。在这个程序中，存储在 BufferReader 中的文本文件是通过使用 for 循环遍历所有行，当条件变为真时，我们将打印这些行*
**实施:****
*my file . txt是要使用的演示文件。*
**这是包含在该文件中的样本行，该文件由以行组成的随机仲裁字组成****
**3D 打印或添加制造是从数字文件制作三维实体对象的过程。****
**3D 打印对象的创建是使用附加过程实现的。在添加过程中，通过铺设连续的材料层直到创建对象，来创建对象。这些层中的每一层都可以看作是物体的薄片横截面。****
**3D 打印与减法制造相反，减法制造是用例如铣床切割/挖空一块金属或塑料。****
**3D 打印使您能够制作复杂的形状。****
**它比传统制造方法使用更少的材料。****
**Java 语言(一种计算机语言，尤用于创建网站)****
****// Java program to Read Specific Lines from a Text File
// Importing required libraries
import java.io.*;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
// Main class
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Initially taking empty string
String text = "";
// Declaring a variable to lookup for
// number of lines in afile
int lineNumber;
// Try block to check for exceptions
try {
// Creating a FileReader object so as to
// get the directory of file to be read
FileReader readfile = new FileReader(
"C:\\Users\\HP\\Desktop\\Exam.txt");
// Creating a BufferReader class object to
// read file as passed above
BufferedReader readbuffer
= new BufferedReader(readfile);
// Buffer reader declaration
// Conditionality for specific line/s
// Loop for the traversing line by line
// into the text file
for (lineNumber = 1; lineNumber < 10;
lineNumber++) {
// If spefic line/s is found
if (lineNumber == 7) {
// Store the content of this specific
// line
text = readbuffer.readLine();
}
else {
// Just keep on reading
readbuffer.readLine();
}
}
}
// Catching IOException exception
catch (IOException e) {
// Print the line number where exception occurred
e.printStackTrace();
}
// Print the specific line from the file read
System.out.println(" The specific Line is: "
+ text);
}
}****
*输出:具体线路为:*
**3D printing enables you to produce complex shapes.**
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