Question

如何在java中以有效的方式读取文件？建议任何方法..我使用BufferedReader，这是非常慢..建议任何变化??

CODE：

import java.io.*;
import java.awt.*;
import javax.swing.*;
import java.awt.event.*;
import java.lang.StringBuffer;

/*The main class file starts here*/

class TitleCaseRow10 extends JFrame implements ActionListener,FocusListener
{

// Declare the required variables

JButton jbFileLoad,jbFileSave,jbCaseChange;
JLabel jlTitle,jlFileSelect,jlContentDisplay;
Font myFont;
JPanel mainPanel,fileOperationPanel,buttonPanel,fileOpenPanel;
JFrame jframe;
JTextField jtfFileName;
JTextArea jtaFileContent,jtaCaseChange;
JScrollPane jScrPaneContent,jScrPaneCaseChange;
boolean boolFileOk = false;
File file;
String fileName,strFileContent,strBuffer=""; 
JFileChooser fileChooser;

// Constructor method for TitleCaseRow10

TitleCaseRow10(String titleName)
{
    super(titleName);

}

void createAndShowGUI()

/*  This method is used to create the Graphical User Interface
    and show it in the screen.
    This method takes no input parameters 
    nor does it return any value.
*/

{

    // create and set up the window

    jframe = new JFrame();
    jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    jframe.setSize(500,600);

    // create the panels 
    // 1. mainPanel for containing other panels
    // 2. buttonPanel for containing buttons
    // 3. fileOpenPanel for containing file choose text filed
    //   and load file button
    // 4. fileOperationPanel for containing all the file operation objects

    mainPanel = new JPanel();
    buttonPanel = new JPanel();
    fileOperationPanel = new JPanel();
    fileOpenPanel = new JPanel();

    // create a file chooser
    fileChooser = new JFileChooser();

    // create labels and buttons

    jlTitle = new JLabel("TITLE CASE CHANGER",JLabel.CENTER);
    jlFileSelect = new JLabel("Enter the filename or click 'load file'");
    jlContentDisplay = new JLabel("TEXT DISPLAY AREAS",JLabel.CENTER);
    jbFileLoad = new JButton("Load File");  
    jbFileSave = new JButton("Save File");
    jbCaseChange = new JButton("Title Case");   

    //Create  text feild, text area and scroll panes

    jtfFileName = new JTextField(28);
    jtaFileContent = new JTextArea(30,10);
    jtaCaseChange = new JTextArea(30,10);
    jScrPaneContent = new JScrollPane(jtaFileContent);
    jScrPaneCaseChange = new JScrollPane(jtaCaseChange);


    // set up the panels

    fileOperationPanel.setBackground(Color.BLACK);
    fileOpenPanel.setBackground(Color.BLACK);
    buttonPanel.setBackground(Color.BLACK);
    mainPanel.setBackground(Color.BLACK);
    mainPanel.setLayout(new GridLayout(3,0,15,15));
    fileOperationPanel.setLayout(new GridLayout(5,0,5,5));
    fileOpenPanel.setLayout(new FlowLayout());
    buttonPanel.setLayout(new FlowLayout());

    // set up text field, labels and text area

    // set the font
    myFont = new Font("Constantia",1,15);
    jtfFileName.setFont(myFont);
    jlTitle.setFont(myFont);
    jlContentDisplay.setFont(myFont);
    jtaFileContent.setFont(myFont);
    jtaCaseChange.setFont(myFont);
    jlFileSelect.setFont(new Font("Arial",0,14));

    // set line wrap
    jtaFileContent.setLineWrap(true);
    jtaCaseChange.setLineWrap(true);

    //set foreground and background color
    jlTitle.setForeground(Color.WHITE);
    jlContentDisplay.setForeground(Color.WHITE);
    jlFileSelect.setForeground(Color.WHITE);
    jtaFileContent.setForeground(Color.LIGHT_GRAY);
    jtaCaseChange.setForeground(Color.LIGHT_GRAY);
    jtfFileName.setForeground(Color.LIGHT_GRAY);
    jtaFileContent.setBackground(Color.DARK_GRAY);      
    jtaCaseChange.setBackground(Color.DARK_GRAY);
    jtfFileName.setBackground(Color.DARK_GRAY);

    // Set default text to file content text area
    jtaFileContent.setText("Type text here");

    // set up scroll panes

    jScrPaneContent.setAutoscrolls(true);
    jScrPaneCaseChange.setAutoscrolls(true);
    jScrPaneCaseChange.getHorizontalScrollBar();
    jScrPaneCaseChange.getHorizontalScrollBar();

    // add the action listeners to buttons

    jbFileLoad.addActionListener(this);
    jbFileSave.addActionListener(this);
    jbCaseChange.addActionListener(this);   
    jtaFileContent.addFocusListener(this);

    // add all the components

    jframe.add(mainPanel);
    fileOpenPanel.add(jtfFileName);
    fileOpenPanel.add(jbFileLoad);
    buttonPanel.add(jbCaseChange);
    buttonPanel.add(jbFileSave);
    fileOperationPanel.add(jlTitle);
    fileOperationPanel.add(jlFileSelect);
    fileOperationPanel.add(fileOpenPanel);
    fileOperationPanel.add(buttonPanel);
    fileOperationPanel.add(jlContentDisplay);
    mainPanel.add(fileOperationPanel);
    mainPanel.add(jScrPaneContent);
    mainPanel.add(jScrPaneCaseChange);

    // set the frame visible

    jframe.setVisible(true);

}

public void actionPerformed(ActionEvent ae)
{
    String command = ae.getActionCommand();
    if(command.equals("Load File"))
    {
    System.out.println("Load File action");
    fileName = "";
    int retVal = fileChooser.showOpenDialog(this);  
    System.out.println("open dialog...");   
    if(retVal==JFileChooser.APPROVE_OPTION)
    {
        try
        {
        file = fileChooser.getSelectedFile();
        fileName = fileChooser.getCurrentDirectory().getPath();
        fileName = fileName.concat("\\"+file.getName());
        jtfFileName.setText(fileName);
        boolFileOk=true;
        jtaFileContent.setText("");
        BufferedReader br= new BufferedReader(new FileReader(file),1000000);
        while((strFileContent = br.readLine())!=null)
            jtaFileContent.append(strFileContent+"\n");
        }
        catch(Exception e)
        {
        System.out.println("Some problem : "+e);
        }
    }

    }
    if(command.equals("Title Case"))
    System.out.println("Title Case action");
    if(command.equals("Save File"))
    System.out.println("Save File action");

}

public void focusGained(FocusEvent fe)
{
    System.out.println("Focus Gained");
    if(!boolFileOk)
    jtaFileContent.setText("");
}
public void focusLost(FocusEvent fe)
{

    System.out.println("Focus Lost");
}

/*

boolean loadFile(ActionEvent ae)
{

    // Check if the filename textfield is really empty

    if(jtfFileName.getText().trim().equals(""))

    {
    fileName = "";
    int retVal = fileChooser.showOpenDialog(TitleCaseRow10.this);   
    System.out.println("open dialog...");   
    if(retVal==JFileChooser.APPROVE_OPTION)
    {
        try
        {
        file = fileChooser.getSelectedFile();
        fileName = fileChooser.getCurrentDirectory().getPath();
        fileName = fileName.concat("\\"+file.getName());
        jtfFileName.setText(fileName);
        return true;
        }
        catch(Exception e)
        {
            System.out.println("Some problem : "+e);
        }
    }
    }

    return false;
    // returns false if the filename is empty or 
    // if the file is not opened
}

*/


//*****************************************************************

//the main method which creates an 
//instance of the class R10TitleCase

//******************************************************************

public static void main(String args[])
{
    TitleCaseRow10 caseChanger = new TitleCaseRow10("Title Case");
    caseChanger.createAndShowGUI();
}
}

Answer 1

定义“高效”。这取决于您的访问模式。

当你一次从一个字节（或几个字节）读取文件时，BufferedReader会加速，否则它是无用的开销。不过，除非你在代码中做错了或者有不切实际的期望，否则它不应该“非常慢”。

如果您正在阅读非常大的文件，那么java.nio，特别是FileChannel的性能要比java.io好得多。

修改您似乎将文件的内容添加到JTextArea（我假设jtaFileContent是）一次一行 - 那是什么是慢的（因为它必须更新UI每次都涉及很多工作），而不是文件的读取。相反，您应该将所有文本读入StringBuilder，并且只有在拥有所有内容后才更新JTextArea。

但是，如果您的文件非常大，您可能会耗尽内存，并且可能必须查找仅加载正在显示的部分的其他UI组件;应该有类似的东西。

Answer 2

你确定文件IO实际上很慢吗？如果您只是使用硬编码字符串附加相同数量的行，它会快吗？如果是让你放慢速度的GUI，我不会感到惊讶。

顺便说一句，FileReader将使用平台默认编码，这通常是一个坏主意。使用具有特定编码的FileInputStream和InputStreamReader。（然后将其包裹在BufferedReader当然。）你也应该尝试/最后在结束时关闭阅读器。

Answer 3

问题是你直接附加到jtaFileContent。尝试读入StringBuilder，然后调用jtaFileContent.setText（）

StringBuilder sb = new StringBuilder(100);
for(Scanner sc = new Scanner(new FileReader(fileName)); sc.hasNext(); )
  sb.append(sc.nextLine());

jtaFileContent.setText(sb.toString());

Answer 4

这里有一些有用的方法。在这三种方法之间，您可以将文件或资源读入String。我一直都在使用它们。我希望你发现它们很有用：

/**
* Takes the file and returns it in a string
*
* @param location on the disc
* @return the file in string form
* @throws IOException
*/
public static String fileToString(String location) throws IOException {
  FileReader fr = new FileReader(new File(location));
  return readerToString(fr);
}

/**
* Takes the given resource (based on the given class) and returns that as a string.
*
* @param location relative to the given class (for example "/resources/textFile.txt")
* @param c the class the location is relative to
* @return the file in string form
* @throws IOException
*/
public static String resourceToString(String location, Class c) throws IOException {
  InputStream is = c.getResourceAsStream(location);
  InputStreamReader r = new InputStreamReader(is);
  return readerToString(r);
}

/**
* Returns all the lines in the scanner's stream as a String
*
* @param r the InputStreamReader to read
* @return the InputStreamReader in String form
* @throws IOException
*/
public static String readerToString(InputStreamReader r) throws IOException {
  StringWriter sw = new StringWriter();
  char[] buf = new char[1024];
  int len;
  while ((len = r.read(buf)) > 0) {
    sw.write(buf, 0, len);
  }
  r.close();
  sw.close();
  return sw.toString();
}

高效的文件阅读方式

4 个答案: