如何使用Java写/读/写内存

Question

Following java code is reading value from JSON File ,using freemarker template its storing JSON value and write that new structure with JSON key and value to text file and save to path mentioned ,and after that from mentioned path text file will be read and it will print that text file to TSC printer.My concern is that I want to store that temporary reading/writing file to memory ,Can any one please help regarding this ,how to store that temporary file to memory ?

Java Code

public class JSONSimpleWritingToFileExample {  
public static void main (String[] args){

//  ************** Reading from JSON file **********

final String filePath = ("C:/Users//Desktop/333.json"); //JSON Path
FileReader reader = null;
try {
         reader = new FileReader(filePath);
         final JSONParser parser = new JSONParser();
         final JSONObject json = (JSONObject) parser.parse(reader);
         final JSONArray jsonUsers = (JSONArray) json.get("Booking");
         final Iterator<?> it = jsonUsers.iterator();
         while (it.hasNext())
         {
                    final JSONObject jsonUser = (JSONObject) it.next();
                    final String bookSrc = (String) jsonUser.get("Key1");
                    final String custName = (String) jsonUser.get("Key2");
                    final String custNum = (String) jsonUser.get("Key3");
                    final String custPName = (String) jsonUser.get("Key4");



// ********* Reading From Template *************                

         Configuration cfg = new Configuration();
try {
        //Load template from source folder
                    Template template = cfg.getTemplate("src/Test.ftl");  // Reading from Template path
        // Build the data-model
                    Map<String, Object> data = new HashMap<String, Object>();
                    data.put("Key1", ""+Value1);
                    data.put("Key2", ""+Value2); 
                    data.put("Key3", ""+Value3);
                    data.put("Key4", ""+Value4);

// Console output
                   Writer out = new OutputStreamWriter(System.out);
                   template.process(data, out);
                   out.flush();

// File output
                   Writer file = new FileWriter (new File("D:\\FTL_helloworld.txt")); // Writing text file path
                   template.process(data, file);
                   file.flush();
                   file.close();

// Reading Text file  & Printing Logic                  

                      FileInputStream textStream;
                  textStream = new FileInputStream("D:/FTL_helloworld.txt");
                  DocFlavor flavor = DocFlavor.INPUT_STREAM.AUTOSENSE;
                  DocAttributeSet das=new HashDocAttributeSet();
                  Doc mydoc = new SimpleDoc(textStream, flavor, das);
                  PrintRequestAttributeSet aset = new HashPrintRequestAttributeSet();
                  aset.add(OrientationRequested.PORTRAIT); 
                  @SuppressWarnings("unused")
                  PrinterJob pj = PrinterJob.getPrinterJob(); 
                  PrintService[] services = PrintServiceLookup.lookupPrintServices(flavor, aset);
                  PrintService defaultService = PrintServiceLookup.lookupDefaultPrintService();
              for (int i = 0; i < services.length; i++) 
                  {
                        System.out.println(services[i].getName());
                  }
             if(services.length == 0) 
                  {
                        if(defaultService == null) 
                  {
                                     //no printer found
                  } 
                 else {
                                    //print using default
                            DocPrintJob job = defaultService.createPrintJob();
                            job.print(mydoc, aset);
                      }
                      } 
                else {

                    PrintService service = ServiceUI.printDialog(null, 200, 200, services, defaultService, flavor, aset);
                    if (service != null)
                       {
                         DocPrintJob job = service.createPrintJob();
                         job.print(mydoc, aset);
                       }
                       }

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

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

 }
}

303 JSON file

{
"Booking": [ {
    "Key1":"Value1",
    "Key2":"Value2",
    "Key3":"Value3",
    "Key4":"Value4"

},
{
    "Key1":"Value1",
    "Key2":"Value2",
    "Key3":"Value3",
    "Key4":"Value4"

}]  
}

Test.ftl

Q799,B080+000
q831
rN
S4
D7
ZT
JF
OD,P
R24,0
N

X555,56,2,780,714
A771,73,1,1,2,1,N,"A  {0}"
A742,70,1,1,2,2,N,"   {1}({31})"
A765,450,1,1,2,2,N,"${Value1}"
A706,86,1,2,1,1,N,"${Value2}"
A682,86,1,2,1,1,N,"${Value3}"
A658,86,1,2,1,1,N,"${Value4}"
P1

Answer 1

Instead of writing the data to a file and then reading it from a file, use a ByteArrayOutputStream and a ByteArrayInputStream (which means your intermediate storage mechanism is a byte array in memory).

FreeMarker's Template class uses a Writer to write output. Instead of using a FileWriter, try constructing an OutputStreamWriter:

ByteArrayOutputStream baos = new ByteArrayOutputStream();
OutputStreamWriter writer = new OutputStreamWriter(baos);
template.process(data, writer);
writer.close();

You can retrieve the data:

byte[] savedData = baos.toByteArray();

Then read it back in:

ByteArrayInputStream bais = new ByteArrayInputStream(savedData);
DocFlavor flavor = DocFlavor.INPUT_STREAM.AUTOSENSE;
DocAttributeSet das = new HashDocAttributeSet();
Doc mydoc = new SimpleDoc(bais, flavor, das);