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();
}
}
答案 0 :(得分：8)
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。
答案 1 :(得分：3)
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。
答案 2 :(得分：2)
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());
答案 3 :(得分：0)
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();
}