java - JAVA中在文件的一行末尾添加特定字符串

Question

我的问题是，我猜，非常简单:

给定一个data.txt文件，如何在java中逐行添加一些字符串？我不想删除内容，但是只需在行尾添加一些字符串即可。您能给我看一个简单的代码吗？

例如，给定 data.txt 文件:

aaa bbb ccc
eee fff ggg

运行java程序后的结果:

aaa bbb ccc ddd
eee fff ggg hhh

<小时/>

附加问题:是否有一种简单的方法可以在给定文件的行中“插入”一些字符串？如果是的话，又该如何做呢？结果:

aaa 111 bbb ccc
eee fff 222 ggg

预先感谢您的帮助。

Answer 1

我不知道有什么简单的方法可以做到这一点，但是有一种相当复杂的方法可以做到这一点，即从文件中读取文本，对其进行编辑，然后用编辑后的文本覆盖文件。首先，您需要将文件逐行读取到数组中:

package addtext;


import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.logging.Level;
import java.util.logging.Logger;
/**
 *
 * @author Dan300
 */
public class AddText {

    File yourFile = new File("YourFileHere.txt"); //add the name of your file in the brackets
    int numLines; //this will store the number of lines in the file
    String[] lines; //the lines of text that make up the file will be stored here

    public AddText() {
        numLines = getNumberLines(yourFile);
        lines = new String[numLines];//here we set the size of the array to be the same as the number of lines in the file
        for(int count = 0; count < numLines; count++) {
            lines[count] = readLine(count,yourFile);//here we set each string in the array to be each new line of the file
        }

        doSomethingToStrings();
    }

public static void main(String[] args) {
        new AddText();
    }

上面的代码基本上通过调用下面的方法(返回文件中文本的行数)来设置一个数组，以包含与文件中的行数一样多的字符串...:

public int getNumberLines(File aFile) {
    int numLines = 0;
    try {

        BufferedReader input =  new BufferedReader(new FileReader(aFile));
            try {
                String line = null;

                while (( line = input.readLine()) != null){ //ReadLine returns the contents of the next line, and returns null at the end of the file.
                    numLines++;
                }
  }
  finally {
    input.close();
  }
}
catch (IOException ex){
  ex.printStackTrace();
}
    return numLines;
}

...然后通过为每一行调用此方法来设置数组以包含文件中的文本:

public String readLine(int lineNumber, File aFile) {
        String lineText = "";
        try {

            BufferedReader input =  new BufferedReader(new FileReader(aFile));
                try {
                     for(int count = 0; count < lineNumber; count++) {
                        input.readLine();  //ReadLine returns the contents of the next line, and returns null at the end of the file.
                     }
                     lineText = input.readLine();
      }
      finally {
        input.close();
      }
    }
    catch (IOException ex){
      ex.printStackTrace();
    }
        return lineText;
    }

读取文本文件后，您现在需要使用将两个字符串连接在一起的 .concat() 方法对字符串执行某些操作。此代码将执行问题中的示例:

public void doSomethingToStrings() {
        try {

            lines[0] = lines[0].concat(" ddd"); //this joins the two strings lines[0] and " ddd"

        } catch (ArrayIndexOutOfBoundsException ex) { // I have added a try{}catch{} block so that if there is not as many lines in the file as expected, the code will still continue.

        }
        try {
            lines[1] = lines[1].concat(" hhh");
        } catch (ArrayIndexOutOfBoundsException ex) {

        }



        try {

            writeFile(yourFile);

        } catch (FileNotFoundException ex) {

        } catch (IOException ex) {
            Logger.getLogger(AddText.class.getName()).log(Level.SEVERE, null, ex);
        }

    }

此后，它调用 writeFile() 方法，该方法会将数组写入文件。如果您想让代码更灵活，您可能希望添加另一个构造函数来将不同的数组写入文件:

public void writeFile(File aFile) throws FileNotFoundException, IOException {
        if (aFile == null) {
      throw new IllegalArgumentException("File should not be null.");
    }
    if (!aFile.exists()) {
      throw new FileNotFoundException ("File does not exist: " + aFile);
    }
    if (!aFile.isFile()) {
      throw new IllegalArgumentException("Should not be a directory: " + aFile);
    }
    if (!aFile.canWrite()) {
      throw new IllegalArgumentException("File cannot be written: " + aFile);
    }

    BufferedWriter output = new BufferedWriter(new FileWriter(aFile));
    try {
        for(int count = 0; count < numLines; count++) {
            output.write(lines[count]);
            if(count != numLines-1) {// This makes sure that an extra new line is not inserted at the end of the file
                output.newLine();
            }

        }

    }
    finally {
      output.close();
    }
    }

要回答您的第二个问题，可以通过使用 StringTokenizer 将字符串拆分为单词，然后将新单词插入到文本行中，从而将一个或多个单词插入一行中。 StringTokenizer 将字符串拆分为单词，并调用 $Tokenizer1.nextToken() 返回字符串中的下一个单词。这是一个示例，其结果在您的问题中指定:

public void doSomethingElseToStrings() {
        try{
        StringTokenizer splitString1 = new StringTokenizer(lines[0]);
        newLines[0] = splitString1.nextToken();
        for(int count=0;count<=splitString1.countTokens();count++) {
            if(count == 0) {
            newLines[0] = newLines[0].concat(" 111");
        }
            newLines[0] = newLines[0].concat(" ");
            newLines[0] = newLines[0].concat(splitString1.nextToken());

        }
        } catch(ArrayIndexOutOfBoundsException ex) {

        }

        try {
        StringTokenizer splitString2 = new StringTokenizer(lines[1]);
        newLines[1] = splitString2.nextToken();
        for(int count=0;count<=splitString2.countTokens();count++) {
            if(count == 1) {
            newLines[1] = newLines[1].concat(" 222");
        }
            newLines[1] = newLines[1].concat(" ");
            newLines[1] = newLines[1].concat(splitString2.nextToken());

        }
        } catch(ArrayIndexOutOfBoundsException ex) {

        }


        try {

            writeFile(yourFile);

        } catch (FileNotFoundException ex) {

        } catch (IOException ex) {
            Logger.getLogger(AddText.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

但是，要使其与其余代码一起使用，您必须编辑这些部分:

public class AddText {  
    String[] newLines; // <<add
    File yourFile = new File("YourFileHere.txt"); //add the name of your file in the brackets
    int numLines; 
    String[] lines; 

public AddText() {
...
//doSomethingToStrings();  <<delete
doSomethingElseToStrings(); //  <<add
}


public void writeFile(File aFile) throws FileNotFoundException, IOException {
...
//output.write(lines[count]); <<delete
output.write(newLines[count]); //  <<add
...
}

使用doSomethingToStrings()方法更改文件:

aaa bbb ccc
eee fff ggg
(other text)

对此:

aaa bbb ccc ddd
eee fff ggg hhh
(other text remains the same)

使用 doSomethingElseToStrings() 方法将文件更改为:

aaa 111 bbb ccc
ddd eee 222 fff
(other text remains the same)

希望这对您有用!