java-文件和I/O

理解IO：http://www.importnew.com/23708.html

一、读写文件：

FileInputStream

该流用于从文件读取数据，它的对象可以用关键字 new 来创建。

有多种构造方法可用来创建对象。

可以使用字符串类型的文件名来创建一个输入流对象来读取文件：

InputStream f = new FileInputStream("C:/java/hello");

也可以使用一个文件对象来创建一个输入流对象来读取文件。我们首先得使用 File() 方法来创建一个文件对象：

File f = new File("C:/java/hello");

InputStream out = new FileInputStream(f);

FileOutputStream

该类用来创建一个文件并向文件中写数据。

如果该流在打开文件进行输出前，目标文件不存在，那么该流会创建该文件。

有两个构造方法可以用来创建 FileOutputStream 对象。

使用字符串类型的文件名来创建一个输出流对象：

OutputStream f = new FileOutputStream("C:/java/hello")

也可以使用一个文件对象来创建一个输出流来写文件。我们首先得使用File()方法来创建一个文件对象：

File f = new File("C:/java/hello");

OutputStream f = new FileOutputStream(f);

import java.io.*;
 
public class fileStreamTest2{
  public static void main(String[] args) throws IOException {
    
    File f = new File("a.txt");
    // 构建FileOutputStream对象,文件不存在会自动新建
    FileOutputStream fop = new FileOutputStream(f);
    // 构建OutputStreamWriter对象,参数可以指定编码,默认为操作系统默认编码,windows上是gbk
    OutputStreamWriter writer = new OutputStreamWriter(fop, "UTF-8");
    // 写入到缓冲区
    writer.append("中文输入");
    //换行
    writer.append("
");
    // 刷新缓存冲,写入到文件,如果下面已经没有写入的内容了,直接close也会写入
    writer.append("English");
    //关闭写入流,同时会把缓冲区内容写入文件,所以上面的注释掉
    writer.close();
    // 关闭输出流,释放系统资源
    fop.close();
 


    // 构建FileInputStream对象
    FileInputStream fip = new FileInputStream(f);
    // 构建InputStreamReader对象,编码与写入相同
    InputStreamReader reader = new InputStreamReader(fip, "UTF-8");
      // 转成char加到StringBuffer对象中
    StringBuffer sb = new StringBuffer();
    while (reader.ready()) {
      sb.append((char) reader.read());
    }
    System.out.println(sb.toString());
    // 关闭读取流
    reader.close();
    // 关闭输入流,释放系统资源
    fip.close();
 
  }
}

 写文件：

String tPath = request.getSession().getServletContext().getRealPath("/");
        FileOutputStream outputStream = null;
        try {
            if (fileType.equals("doc") || fileType.equals("docx")) {
                String folderPath = tPath.substring(0,tPath.lastIndexOf("\")) + "/uploadfiles/conferencefile/"+topicInfo.getId();
                tPath = folderPath +"/"+ fileName + "." + fileType;
                //--------写入文件内容-----------------
                File folder = new File(folderPath);
                if(!folder.exists())    
                {   
                    folder.mkdirs();    
                }    
                File file = new File(tPath);
                if(!file.exists())    
                {   
                    try {    
                        file.createNewFile();    
                    } catch (IOException e) {  
                        e.printStackTrace();    
                    }    
                }    
                outputStream = new FileOutputStream(file);
                byte[] bytes = Base64.decodeBase64(base64String);
                outputStream.write(bytes,0,bytes.length);
                //-----------------------------------
            }
        } catch (Exception e) {
        }
        finally {
            try {
                outputStream.close();
            } catch (IOException e) {
                // TODO 自动生成的 catch 块
                e.printStackTrace();
            }
        }

二、创建目录：

判断文件是否存在

File file = new File(filePath + builder.toString());
        if(!file.exists())    
        {    
            try {    
                file.createNewFile();    
            } catch (IOException e) {  
                e.printStackTrace();    
            }    
        }    

判断文件夹是否存在

File类中有两个方法可以用来创建文件夹：

• mkdir( )方法创建一个文件夹，成功则返回true，失败则返回false。失败表明File对象指定的路径已经存在，或者由于整个路径还不存在，该文件夹不能被创建。
• mkdirs()方法创建一个文件夹和它的所有父文件夹。

File filePath = new File("D:\Video");
if (!filePath.exists()) {
     filePath.mkdirs();
}

三、读取目录：

判断是文件夹还是文件

import java.io.File;
 
public class DirList {
  public static void main(String args[]) {
    String dirname = "/tmp";
    File f1 = new File(dirname);
    if (f1.isDirectory()) {
      System.out.println( "目录 " + dirname);
      String s[] = f1.list();
      for (int i=0; i < s.length; i++) {
        File f = new File(dirname + "/" + s[i]);
        if (f.isDirectory()) {
          System.out.println(s[i] + " 是一个目录");
        } else {
          System.out.println(s[i] + " 是一个文件");
        }
      }
    } else {
      System.out.println(dirname + " 不是一个目录");
    }
  }
}

四、删除目录或文件

删除文件可以使用 java.io.File.delete() 方法。

删除文件及目录

//删除文件及目录
  public static void deleteFolder(File folder) {
    File[] files = folder.listFiles();
        if(files!=null) { 
            for(File f: files) {
                if(f.isDirectory()) {
                    deleteFolder(f);
                } else {
                    f.delete();
                }
            }
        }
        folder.delete();
    }

五、读写excel文件

需要jxl.jar jar包支持，jxl.jar好像不支持.xlsx格式excel文件，需要把.xlsx格式的excel文件另存为.xls格式文件

使用poi读取excel文件，HSSFWorkbook与XSSFWorkbook，前一个可以用来解析以.xls结尾的excel，后一个可以用来解析.xlsx结尾的excel

poi:

//读取excel文件内容
            List<User> userExcel = new ArrayList<>();
            File file = null;
            try {
                file = new File(filePath);
            } catch (Exception e) {
                responseResult.setMsg("检查文件路径是否正确："+filePath);
                return responseResult;
            }
            FileInputStream fStream = new FileInputStream(file);
            XSSFWorkbook xss = new XSSFWorkbook(fStream);
            XSSFSheet sheet = xss.getSheetAt(0);
            for(int i=0;i<sheet.getLastRowNum();i++) {
                Row row = sheet.getRow(i);
                User user = new User();
                for(int j=0;j<row.getLastCellNum();j++) {
                    Cell cell = row.getCell(j, Row.CREATE_NULL_AS_BLANK);
                    switch (cell.getCellType()) {
                    case Cell.CELL_TYPE_BLANK:
                        
                        break;
                    case Cell.CELL_TYPE_BOOLEAN:
                       
                        break;
                    case Cell.CELL_TYPE_NUMERIC:
                        // 数值
                        
                        break;
                    case Cell.CELL_TYPE_STRING:
                        if (i != 0) {
                            String valueStr = cell.getStringCellValue();
                            if (j == 7) {
                                //登录名
                                user.setUserLoginNameHY(valueStr);
                            }else if (j == 9) {
                                //身份证
                                user.setUserCardEncryptionHY(valueStr);
                            }
                        }
                        break;
                    case Cell.CELL_TYPE_ERROR:
                        
                        break;
                    default:
                        break;
                    }
                }
                if (i!=0) {
                    userExcel.add(user);
                }
                
            }

jxl:

public void readExcel(File file) {
        try {  
            //读取excel文件内容
            List<ExcelPollution> listPollution = new ArrayList<>();
            List<ExcelClinic> listClinic = new ArrayList<>();
            // 创建输入流，读取Excel  
            InputStream is = new FileInputStream(file.getAbsolutePath());  
            // jxl提供的Workbook类  
            Workbook wb = Workbook.getWorkbook(is);  
            // Excel的页签数量  
            //int sheet_size = wb.getNumberOfSheets();  
            //for (int index = 0; index < sheet_size; index++)
            {  
                // 每个页签创建一个Sheet对象  
                Sheet sheet = wb.getSheet(0);
                // sheet.getRows()返回该页的总行数  
                for (int i = 0; i < sheet.getRows(); i++) { 
                    ExcelPollution excelPollution = new ExcelPollution(); 
                    // sheet.getColumns()返回该页的总列数  
                    for (int j = 0; j < sheet.getColumns(); j++) {  
                        String cellinfo = sheet.getCell(j, i).getContents();  
                        if (j == 0) {
                            excelPollution.setLocation(cellinfo);
                        }
                        else if (j == 1) {
                            String dString = cellinfo;
                            if (i > 0) {
                                dString = "20" + cellinfo.replace("-", "/");
                            }
                            excelPollution.setDate(dString);
                        }
                        else if (j == 2) {
                            excelPollution.setSO2(cellinfo);
                        }
                        else if (j == 3) {
                            excelPollution.setNO2(cellinfo);
                        }
                        else if (j == 4) {
                            excelPollution.setPM10(cellinfo);
                        }
                        else if (j == 5) {
                            excelPollution.setCO(cellinfo);
                        }
                        else if (j == 6) {
                            excelPollution.setO3(cellinfo);
                        }
                        else if (j == 7) {
                            excelPollution.setPM25(cellinfo);
                        } 
                    }  
                    listPollution.add(i, excelPollution);
                }  
            }  
            
            File file2 = new File("D://Java//DoWork//clinic1.xls");  
            // 创建输入流，读取Excel  
            InputStream is2 = new FileInputStream(file2.getAbsolutePath());  
            // jxl提供的Workbook类  
            Workbook wb2 = Workbook.getWorkbook(is2);  
            // Excel的页签数量  
            //int sheet_size2 = wb2.getNumberOfSheets();  
            //for (int index = 0; index < sheet_size2; index++) 
            {  
                // 每个页签创建一个Sheet对象  
                Sheet sheet2 = wb2.getSheet(1);
                // sheet.getRows()返回该页的总行数  
                for (int i = 0; i < sheet2.getRows(); i++) { 
                    ExcelClinic excelClinic = new ExcelClinic(); 
                    // sheet.getColumns()返回该页的总列数  
                    for (int j = 0; j < sheet2.getColumns(); j++) {  
                        String cellinfo = sheet2.getCell(j, i).getContents();  
                        if (j == 0) {
                            excelClinic.setStation(cellinfo);
                        }
                        else if (j == 1) {
                            String dString = cellinfo;
                            if (i > 0) {
                                dString = "20" + cellinfo.replace("-", "/");
                            }
                            excelClinic.setDate(dString);
                        }
                        else if (j == 2) {
                            excelClinic.setSO2(cellinfo);
                        }
                        else if (j == 3) {
                            excelClinic.setNO2(cellinfo);
                        }
                        else if (j == 4) {
                            excelClinic.setPM10(cellinfo);
                        }
                        else if (j == 5) {
                            excelClinic.setCO(cellinfo);
                        }
                        else if (j == 6) {
                            excelClinic.setO3(cellinfo);
                        }
                        else if (j == 7) {
                            excelClinic.setPM25(cellinfo);
                        }
                        else if (j == 8) {
                            excelClinic.setDiagnose(cellinfo);
                        }
                        else if (j == 9) {
                            excelClinic.setICD_10(cellinfo);
                        }
                        else if (j == 10) {
                            String dString = cellinfo;
                            if (i > 0) {
                                dString = "20" + cellinfo.replace("-", "/");
                            }
                            excelClinic.setDate_birth(dString);
                        }
                        else if (j == 11) {
                            excelClinic.setAge_0(cellinfo);
                        }
                        else if (j == 12) {
                            excelClinic.setGender(cellinfo);
                        }
                        else if (j == 13) {
                            excelClinic.setAge_1(cellinfo);
                        }
                        else if (j == 14) {
                            String dString = "20" + cellinfo.replace("-", "/");
                            excelClinic.setDate_discharge(dString);
                        }
                        else if (j == 15) {
                            excelClinic.setRegisted_address(cellinfo);
                        }
                        else if (j == 16) {
                            excelClinic.setAdmission_cost(cellinfo);
                        }
                        else if (j == 17) {
                            excelClinic.setAddress_present(cellinfo);
                        }
                        else if (j == 18) {
                            excelClinic.setICD(cellinfo);
                        }
                        else if (j == 19) {
                            excelClinic.setID(cellinfo);
                        }
                    }
                    
                    listClinic.add(i, excelClinic);
                }  
            }  
            
            if (listClinic.size() >0 && listPollution.size() > 0) {
                for (ExcelClinic clinic : listClinic) {
                    for (ExcelPollution pollution : listPollution) {
                        if (pollution.getLocation().equals(clinic.getStation()) && pollution.getDate().equals(clinic.getDate())) {
                            clinic.setSO2(pollution.getSO2());
                            clinic.setNO2(pollution.getNO2());
                            clinic.setPM10(pollution.getPM10());
                            clinic.setCO(pollution.getCO());
                            clinic.setO3(pollution.getO3());
                            clinic.setPM25(pollution.getPM25());
                            try {
                                if (pollution.getPM10().equals("PM10") && pollution.getPM25().equals("PM2.5")) {
                                    clinic.setPMc("PMc");
                                }
                                else if (!pollution.getPM10().equals("") && !pollution.getPM25().equals("") && pollution.getPM10() != null && pollution.getPM25() != null) {
                                    Integer pMc = Integer.parseInt(clinic.getPM25()) - Integer.parseInt(clinic.getPM10());
                                    clinic.setPMc(pMc.toString());
                                }
                            } catch (Exception e) {
                                e.printStackTrace();
                            }
                            break;
                        }
                    }
                }
            }
                      
            //按照对象中的date日期进行排序
            Collections.sort(listClinic, new Comparator<ExcelClinic>() {
                @Override
                public int compare(ExcelClinic o1, ExcelClinic o2) {
                    SimpleDateFormat format = new SimpleDateFormat("yyyy/MM/dd");
                    try {
                        Date dt1 = format.parse(o1.getDate());
                        Date dt2 = format.parse(o2.getDate());
                        if (dt1.getTime() > dt2.getTime()) {
                            return 1;
                        } else if (dt1.getTime() < dt2.getTime()) {
                            return -1;
                        } else {
                            return 0;
                        }
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                    return 0;
                }
            });

            //写入excel文件
            try {  
                // 打开文件  
                WritableWorkbook book = Workbook.createWorkbook(new File("D://Java//DoWork//test.xls"));  
                // 生成名为“sheet1”的工作表，参数0表示这是第一页  
                WritableSheet sheet = book.createSheet("sheet1", 0);  
                for (int i = 0; i<listClinic.size();i++) {
                    // 在Label对象的构造子中指名单元格位置是第一列第一行(0,0),单元格内容为string  
                    Label label0 = new Label(0, i, listClinic.get(i).getStation());  
                    // 将定义好的单元格添加到工作表中  
                    sheet.addCell(label0);  
                    Label label1 = new Label(1, i, listClinic.get(i).getDate());  
                    sheet.addCell(label1);  
                    Label label2 = new Label(2, i, listClinic.get(i).getSO2());  
                    sheet.addCell(label2);  
                    Label label3 = new Label(3, i, listClinic.get(i).getNO2());  
                    sheet.addCell(label3);  
                    Label label4 = new Label(4, i, listClinic.get(i).getPM10());  
                    sheet.addCell(label4);  
                    Label label5 = new Label(5, i, listClinic.get(i).getCO());  
                    sheet.addCell(label5);  
                    Label label6 = new Label(6, i, listClinic.get(i).getO3());  
                    sheet.addCell(label6);  
                    Label label7 = new Label(7, i, listClinic.get(i).getPM25());  
                    sheet.addCell(label7);
                    Label label8 = new Label(8, i, listClinic.get(i).getPMc());  
                    sheet.addCell(label8);  
                    Label label9 = new Label(9, i, listClinic.get(i).getDiagnose());  
                    sheet.addCell(label9);  
                    Label label10 = new Label(10, i, listClinic.get(i).getICD_10());  
                    sheet.addCell(label10);  
                    Label label11 = new Label(11, i, listClinic.get(i).getDate_birth());  
                    sheet.addCell(label11);  
                    Label label12 = new Label(12, i, listClinic.get(i).getAge_0());  
                    sheet.addCell(label12);  
                    Label label13 = new Label(13, i, listClinic.get(i).getGender());  
                    sheet.addCell(label13);  
                    Label label14 = new Label(14, i, listClinic.get(i).getAge_1());  
                    sheet.addCell(label14);  
                    Label label15 = new Label(15, i, listClinic.get(i).getDate_discharge());  
                    sheet.addCell(label15);  
                    Label label16 = new Label(16, i, listClinic.get(i).getRegisted_address());  
                    sheet.addCell(label16);  
                    Label label17 = new Label(17, i, listClinic.get(i).getAdmission_cost());  
                    sheet.addCell(label17);  
                    Label label18 = new Label(18, i, listClinic.get(i).getAddress_present());  
                    sheet.addCell(label18);  
                    Label label19 = new Label(19, i, listClinic.get(i).getICD());  
                    sheet.addCell(label19);  
                    Label label20 = new Label(20, i, listClinic.get(i).getID());  
                    sheet.addCell(label20);  
                }
                
                // 写入数据并关闭文件  
                book.write();  
                book.close();  
            } catch (Exception e) {  
                System.out.println(e);  
            }  
        } catch (Exception e) {  
            e.printStackTrace();  
        }        
    }

六、读取文件内容：

org.apache.commons.codec.binary.Base64
 

String path = tPath.substring(0,tPath.lastIndexOf("\")) + file.getUrl();
File f = new File(path);
InputStream iStream = new FileInputStream(f);
byte[] bytes = new byte[(int)f.length()];//或new byte[iStream.available()]
iStream.read(bytes);
String content = new String(Base64.encodeBase64(bytes),"utf-8");
iStream.close();
//------------------------------------------------------------------------------



InputStream inputStream = new BufferedInputStream(new FileInputStream(file));
InputStreamReader iReader = new InputStreamReader(inputStream);

char len;
while (iReader.ready()) {
len = (char) iReader.read();
String string2 = String.valueOf(len);
ss += string2;
}
inputStream.close();
iReader.close();

 问题：

1、代码调试正常，发布war包在tomcat运行，读取html页面内容出现乱码：

原因：读取的时候，编码没有设置（修改为UTF-8读取）

例：

OutputStreamWriter bw = null;
FileOutputStream fop = null;
BufferedReader br =null;
InputStreamReader isr=null;
FileInputStream fis=null;

File file = new File(filename);
fop = new FileOutputStream(file);
bw = new OutputStreamWriter(fop, "UTF-8");
.....
                        
File fileR = new File(fromPath);
fis = new FileInputStream(fileR);  
isr = new InputStreamReader(fis, "UTF-8");
br = new BufferedReader(isr);

String tempStr;
String len="";
while((tempStr = br.readLine()) != null)
{
　　len += tempStr;
}

  // 关闭输入流,释放系统资源
  iStream.close();
  iReader.close();
  br.close();

 效率较高：

InputStream inputStream = null;
BufferedInputStream input = null;
ByteArrayOutputStream outputStream  = null;
try {
    inputStream = ftpClient.retrieveFileStream(fileName);
    input = new BufferedInputStream(inputStream);
    outputStream = new ByteArrayOutputStream();
    byte[] buffer = new byte[1024];
    int len = -1;
    while ((len=input.read(buffer))!=-1){
          outputStream.write(buffer,0,len);
    }
xmlStr = new String( outputStream.toByteArray(),"GBK");
}

bufferedInputStream = new BufferedInputStream(inputStream);
byte[] bytes = new byte[inputStream.available()];
bufferedInputStream.read(bytes);
xmlStr = new String(bytes,"GBK");

int len;
while ((len = bInputStream.read(bytes)) != -1){
          outputStream.write(bytes,0,len);
}

BASE64Encoder encoder = new BASE64Encoder();
String base64Str = encoder.encode(outputStream.toByteArray());

 效率较低：

String len;
while ((len = bufferedReader.readLine()) != null){
       xmlStr += len;
}