java使用stream流批量读取并合并文件，避免File相关类导致单文件过大造成的内存溢出。

import java.io.BufferedReader;

import java.io.File;

import java.io.FileInputStream;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.InputStreamReader;

import java.io.OutputStreamWriter;

import java.util.Iterator;

import java.util.LinkedHashSet;

import java.util.Set;

public class MergeFileByStream {

    /** 跨平台的换行符  */

    public static final String LINE_SEPARATOR = System.getProperty("line.separator");

    /**

     * 合并文件  outFileName为路径+文件名

     * @Method       mergeFiles

     * @Description  TODO

     * @Author           LBH

     * @Date         2015-3-23 下午4:26:54

     * @param

     * @return       boolean

     */

    public boolean mergeFiles(String outFileName, Set<String> files) {

        boolean mergeResule = false;// 结果

        InputStreamReader inputStreamReader = null;

        BufferedReader bufferedReader = null;

        String inputEncoding = "UTF-8";

        try {

            // 验证是否已存在输出文件，存在就删除

            File outFile = new File(outFileName);

            if (outFile.exists()) {

                outFile.delete();

            }

            int i = 0;// 循环计数

            Iterator<String> filesIt = files.iterator();

            if (filesIt != null && files.size() > 1) {

                File inFile = new File(filesIt.next());

                inputStreamReader = new InputStreamReader(new FileInputStream(

                        inFile), inputEncoding);

                bufferedReader = new BufferedReader(inputStreamReader);

                // 开始处理文件

                if (bufferedReader != null && bufferedReader.ready()) {

                    if (i == 0) { // 如果是首个文件，那么除去最后一行保留前两行再写入

                        mergeResule = handleFile("fist", bufferedReader,outFileName, inputEncoding);

                    } else if (i == files.size() - 1) { // 如果是最后一个文件，那么去除前两行，保留最后一行

                        mergeResule = handleFile("last", bufferedReader,outFileName, inputEncoding);

                    } else { // 其他则同时去除前两行和最后一行

                        mergeResule = handleFile("normal", bufferedReader,outFileName, inputEncoding);

                    }

                }

                // 删除该文件

                inFile.delete();

                i++;

            } else if (filesIt != null && files.size() == 1) {// 若只有一个文件，那么直接改名字

                File inFile = new File(filesIt.next());

                inFile.renameTo(new File(outFileName));

            }

        } catch (Exception e) {

            e.printStackTrace();

        }

        // 关闭

        finally {

            if (bufferedReader != null) {

                try {bufferedReader.close();} catch (Exception e) {e.printStackTrace();}

                }

            if (inputStreamReader != null) {

                try {inputStreamReader.close();} catch (Exception e) {e.printStackTrace();

                }

            }

        }

        return mergeResule;

    }

    /**

     * 处理单个文件，读取后立即写入， type:fist--首个文件；last--末个文件；以及其他文件

     *

     * @Method handleFile

     * @Author lbh

     * @Date 2014-12-11 上午09:49:19

     */

    public static boolean handleFile(String type, BufferedReader bufferedReader, String outFile, String outEncoding) {

        boolean handleResult = false; // 是否成功

        FileOutputStream fileOutputStream = null;

        OutputStreamWriter outputStreamWriter = null;

        String readString = ""; // 存放读取数据的变量

        String strA, strB, strC; // 临时变量

        try {

            fileOutputStream = new FileOutputStream(outFile, true);

            outputStreamWriter = new OutputStreamWriter(fileOutputStream, outEncoding);

            if ("fist".equals(type)) { // 首文件的处理

                strA = "";

                strB = "";

                strC = "";

                int fistI = 0;// 计数

                while ((strC = bufferedReader.readLine()) != null) { // 从第一行开始循环读

                    strA = strB;

                    strB = strC;

                    readString = strA + LINE_SEPARATOR;// 最后一行的strB被丢弃

                    // 输出

                    if (fistI > 0) {// 避免第一行空行

                        outputStreamWriter.write(readString);

                        outputStreamWriter.flush();

                    }

                    fistI++;

                }

                handleResult = true;

            }

            if ("last".equals(type)) { // 末文件的处理

                strA = "";

                bufferedReader.readLine();

                bufferedReader.readLine(); // 执行两次，已读取并丢弃了前两行。

                while ((strA = bufferedReader.readLine()) != null) { // 开始循环读

                    readString = strA + LINE_SEPARATOR;

                    // 输出

                    outputStreamWriter.write(readString);

                    outputStreamWriter.flush();

                }

                handleResult = true;

            } else { // 其他文件的处理

                strA = "";

                strB = "";

                strC = "";

                bufferedReader.readLine();

                bufferedReader.readLine(); // 执行两次，已读取并丢弃了前两行。

                long i = 0;

                while ((strC = bufferedReader.readLine()) != null) { // 开始循环读

                    strA = strB;

                    strB = strC;

                    readString = strA + LINE_SEPARATOR;// 最后一行的strB被丢弃

                    // 输出

                    if (i > 0) {// 避免第一行空行

                        outputStreamWriter.write(readString);

                        outputStreamWriter.flush();

                    }

                    i++;

                }

                handleResult = true;

            }

        } catch (IOException e) {e.printStackTrace();}

        // 关闭

        finally {

            if (fileOutputStream != null) {

                try {fileOutputStream.close();} catch (Exception e) {e.printStackTrace();}

                }

            if (outputStreamWriter != null) {

                try {outputStreamWriter.close();} catch (Exception e) {e.printStackTrace();

                }

            }

        }

        return handleResult;

    }

     public static void main(String[] args) throws Exception{

            System.out.println("开始");

            Set<String> ssss = new LinkedHashSet<String>();

            ssss.add("E:\\111\\xmlTest\\a.xml");

            ssss.add("E:\\111\\xmlTest\\b.xml");

            ssss.add("E:\\111\\xmlTest\\c.xml");

            MergeFileByStream st = new MergeFileByStream();

            st.mergeFiles("E:\\111\\xmlTest\\stream2.xml", ssss);

            System.out.println("结束");

        }

}