java.io.RandomAccessFile的使用，指定位置插入字符串（覆盖插入）。jdk1.4增加内存映射文件FileChannel、MappedByteBuffer

　　　//目的是在java文件中插入属性和getter、setter方法　
//找到最后一个}的结束位置，插入内容，并把}补上，}的ascii码是125
　　　　RandomAccessFile randomAccessFile = null;
        try {
            Field[] fields_beihai = com.supermap.realestate.registration.model.genrt.GenerateBDCS_TDYT_GZ.class.getDeclaredFields();

            Field[] fields = com.supermap.realestate.registration.model.genrt.GenerateBDCS_TDYT_GZ.class.getDeclaredFields();

//            Class cls = com.supermap.realestate.registration.model.genrt.GenerateBDCS_TDYT_GZ.class;
            
            Class cls = Test.class;

            String modelName = cls.getSimpleName();
            String packagepath = cls.getPackage().getName().replaceAll("\.","/");
            String root = Thread.currentThread().getContextClassLoader().getResource("").getPath();
            root = root.replace("target/classes", "src/main/java");
            System.out.println(root + packagepath);
            File file = new File(root + packagepath);
            if(!file.isDirectory()) return;
            File[] files = file.listFiles();
            File modelFileResult = null;
            for (File modelFile : files) {
                String model = modelFile.getName();
                if(!model.contains(".java")) continue;
                if(!model.contains(modelName)) continue;
                modelFileResult = modelFile;
                break;
            }
            if(modelFileResult == null) return;
            System.out.println(modelFileResult.getAbsolutePath());

            randomAccessFile = new RandomAccessFile(modelFileResult,"rw");
            byte[] bytes = new byte[100];
            int len = 0;
            String aa = "";
            long start = randomAccessFile.getFilePointer();
            System.out.println("point=" + start);
            long total = randomAccessFile.length();
            System.out.println("total=" + randomAccessFile.length());

            int lastLen = 1;

            randomAccessFile.seek(total - lastLen); //从最后一个字符读取，判断是不是}，是就插入新的内容
            byte lastChar = 0;
　　　　　　　　// }的ascii码是125，找到最后一个}的位置，插入内容

            while((total - lastLen)>=0 && (lastChar = randomAccessFile.readByte()) != 125){
                System.out.println(lastLen++);
                randomAccessFile.seek(total - lastLen);
            }
            System.out.println(new String(new byte[]{lastChar}));
            start = total - lastLen;
            System.out.println("point=" + start);

            randomAccessFile.seek(start);
            randomAccessFile.write("
	private String id;
	public void setId(String id){
		this.id = id;
	}
}".getBytes());



        } catch (Exception e) {
            e.printStackTrace();
        }finally {
            try {
                if(randomAccessFile != null ) randomAccessFile.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

内存映射文件：

import java.io.RandomAccessFile;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;

public class LargeMappedFiles {
static int length = 0x8000000; // 128 Mb

public static void main(String[] args) throws Exception {
// 为了以可读可写的方式打开文件，这里使用RandomAccessFile来创建文件。
FileChannel fc = new RandomAccessFile("test.dat", "rw").getChannel();
//注意，文件通道的可读可写要建立在文件流本身可读写的基础之上
MappedByteBuffer out = fc.map(FileChannel.MapMode.READ_WRITE, 0, length);
//写128M的内容
for (int i = 0; i < length; i++) {
out.put((byte) 'x');
}
System.out.println("Finished writing");
//读取文件中间6个字节内容
for (int i = length / 2; i < length / 2 + 6; i++) {
System.out.print((char) out.get(i));
}
fc.close();
}
}