如何在Java的jtextArea中附加50 mb数据（来自文本文件）？

Question

I have a big file which is having 50 mb data.I want to read and append into jTextArea(). But i am getting out of * memory error * while appending data.How can i do this?please anyone help me

example:

BufferedReader br;
        StringBuilder builder = new StringBuilder();
        try {
            br = new BufferedReader(new FileReader("D:\\myFile.txt"));
            String line;
            try {
                while ((line = br.readLine()) != null) {
                   // process the line.
                    builder.append(line);// here getting error
                }
                System.out.println(builder.toString());

            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            try {
                br.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
JTextArea jt = new JtextArea();
jt.append(builder.toString();

Answer 1

Either you can increase the maximum heap size, or you can use the paginator design pattern.

Pagination works by loading only those data that are actually visible. So if your text area can display two pages of text, you load only those two displayed pages of text at a time. If the user scrolls down, you throw away loaded pages and load those new two. That way, you will always have only two pages in memory at a time.

Answer 2

尝试设置JVM的最大大小

Answer 3

I doubt there will ever be a user to read the 50MB of text that you would add to your JTextArea .

I suggest you implement some sort of pagination and only add a few 100s or 1000s of lines at once.

However, if you really want to add all the text then set the -Xmx parameter of your application to something higher.

Answer 4

Ignoring that it is impractical in terms of usability (and JTextArea will probably not perform well with that much text), you can make some changes to your code to reduce the amount of memory needed (You probably still need to increase -Xmx).

Your first lever is to properly size the StringBuilder for the amount of data you want to put into it. Replacing the new StringBuilder() with new StringBuilder(sizeOfFile) will avoid allocating more memory than needed (this may make a difference of several MB, due to StringBuilders internal memory allocation policy method).

Now when you do builder.toString() , you should be aware that this will double the amount of memory required, since everything in the builder is copied to create the String. With the normal Swing API, there is no way around that, since you absolutely need a String.

But you can change that - look at how the JTextArea works internally: the JTextArea does not really store the text it works with - storing of the text is delegated to a model object, in this case of type javax.swing.Document. If you take a look at Document, you'll find that its an interface. Normally when you use a JTextArea, it creates its own, private document which is not really intended for such large amounts of data (javax.swing.PlainDocument). Now the PlainDocument in turn works with a javax.swing.Content (again an interface), normally implemented in javax.swing.StringContent. This you can replace with your own, new content class that works with a StringBuilder directly (that way there would be no need to duplicate data in memory).

So, you can implement your own Content class working with StringBuilder and construct your JTextArea this way:

Content c = new StringBuilderContent(builder);
Document d = new PlainDocument(c);
JTextArea jt = new JTextArea(d);

Actually creating and implementing StringBuilderContent is left as an excercise to the reader. Actually, you could also implement Content to directly work with a file, that way you could handle files much larger than available heap, too.