BufferedReader和FileChannel读文件比较

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.InputStreamReader;
import java.io.RandomAccessFile;
import java.nio.CharBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import javax.swing.JTextArea;

public class Test {
    
    public static void main(String[] args) throws InterruptedException {
        long startFreeMemory = Runtime.getRuntime().freeMemory();
        System.out.println("start free memory is: " + startFreeMemory);
        try {
            new Test().go2();
            
            long endFreeMemory = Runtime.getRuntime().freeMemory();
            System.out.println("end free memory is: " + endFreeMemory);
        } catch (Exception e) {
            long endFreeMemory = Runtime.getRuntime().freeMemory();
            System.out.println("end free memory is: " + endFreeMemory);
            
            e.printStackTrace();
        }

    }
    
    public void go1() throws Exception {
        FileChannel fChannel = new RandomAccessFile("temp", "r").getChannel();
        MappedByteBuffer mByteBuffer = fChannel.map(FileChannel.MapMode.READ_ONLY, 0, fChannel.size());
        Charset charset = Charset.forName("iso-8859-1");
        CharsetDecoder decoder = charset.newDecoder();
        CharBuffer charBuffer = CharBuffer.allocate(1024);
        charBuffer = decoder.decode(mByteBuffer);
        JTextArea jta = new JTextArea();
        System.out.println("set text length = " + new String(charBuffer.array(), 0, charBuffer.limit()).length());
        
        jta.setText(new String(charBuffer.array(), 0, charBuffer.limit()));
        fChannel.close();
    }
    
    public void go2() throws Exception {
    	String text = "";
        BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream("temp")));
        String line = null;
        JTextArea jta = new JTextArea();
        while ((line = br.readLine()) != null) {
        	text += line;
        	text += "\n";
        	jta.setText(text);
//            jta.append(line);     //使用此处屏蔽的两行就会内存溢出
//            jta.append("\n");
            System.out.println(line);
        }
        br.close();

    }
}

 

使用此处屏蔽的两行替换setText方式就会溢出，原因在于JTextArea的append方法有更严格的限制：

最终会进入javax.swing.text.BoxView类的如下方法：

/**
     * Resizes the given layout array to match the new number of
     * child views.  The current number of child views are used to
     * produce the new array.  The contents of the old array are
     * inserted into the new array at the appropriate places so that
     * the old layout information is transferred to the new array.
     *
     * @param oldArray the original layout array
     * @param offset location where new views will be inserted
     * @param nInserted the number of child views being inserted; 
     *		therefore the number of blank spaces to leave in the
     *		new array at location <code>offset</code>
     * @return the new layout array
     */
    int[] updateLayoutArray(int[] oldArray, int offset, int nInserted) {
	int n = getViewCount();
	int[] newArray = new int[n];

	System.arraycopy(oldArray, 0, newArray, 0, offset);
	System.arraycopy(oldArray, offset, 
			 newArray, offset + nInserted, n - nInserted - offset);
	return newArray;
    }

 

 

错误堆栈：

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
    at javax.swing.text.BoxView.updateLayoutArray(BoxView.java:194)
    at javax.swing.text.BoxView.replace(BoxView.java:168)
    at javax.swing.text.View.updateChildren(View.java:1095)
    at javax.swing.text.View.insertUpdate(View.java:679)
    at javax.swing.plaf.basic.BasicTextUI$RootView.insertUpdate(BasicTextUI.java:1589)
    at javax.swing.plaf.basic.BasicTextUI$UpdateHandler.insertUpdate(BasicTextUI.java:1848)
    at javax.swing.text.AbstractDocument.fireInsertUpdate(AbstractDocument.java:185)
    at javax.swing.text.AbstractDocument.handleInsertString(AbstractDocument.java:734)
    at javax.swing.text.AbstractDocument.insertString(AbstractDocument.java:693)
    at javax.swing.text.PlainDocument.insertString(PlainDocument.java:114)
    at javax.swing.JTextArea.append(JTextArea.java:470)
    at Test.go2(Test.java:48)
    at Test.main(Test.java:18)

同样的文件，BufferedReader为什么会失败呢？