java - 读取文件的有效方法

Question

如何在java中高效地读取文件？建议任何方法..我使用BufferedReader，它非常慢..建议任何更改？？

代码:

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。

当您一次从文件中读取一个字节(或几个字节)时，BufferedReader 会加快速度，否则这是无用的开销。尽管如此，它不应该“非常慢”，除非您在代码中做错了什么或者有不切实际的期望。

如果您正在读取非常大的文件，特别是 java.nio FileChannel比java.io有更好的性能。

编辑:您似乎一次一行地将文件的内容添加到 JTextArea (我认为这就是 jtaFileContent ) - 这就是慢的地方(因为它每次都要更新UI，这涉及很多工作)，而不是读取文件。相反，您应该将所有文本读取到 StringBuilder 中，并且只有在获得所有内容后才更新 JTextArea。

但是，如果您的文件非常大，您可能会耗尽内存，并且可能必须寻找不同的 UI 组件来仅加载正在显示的部分；那里应该有类似的东西。