Should the method that receives java.lang.Object as input also accept javax.servlet.jsp.JspWriter as input?

Question

I wanted to combine two functions .

After getting a viable solution, I decided to play around with the code a bit and came up with the following:

package hu.flux.helper; import java.io.DataInputStream; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.io.PrintWriter; import java.io.Writer; import javax.servlet.jsp.JspWriter; import com.objectmentor.library.web.framework.mocks.*; // A holder for formatting data public class NameAndAddress { public String firstName; public String middleName; public String lastName; public String address1; public String address2; public String city; public String state; public String zip; public String FormattedString() { String formattedString = "<PRE>\n" + firstName; // Add the middle name only if it contains data. if ((middleName != null) && (middleName.length() > 0)) {formattedString += " " + middleName;} formattedString += " " + lastName + "\n"; formattedString += address1 + "\n"; if ((address2 != null) && (address2.length() > 0)) formattedString += address2 + "\n"; formattedString += city + ", " + state + " " + zip + "\n</PRE>"; return formattedString; } // Print out the name and address. public void print(Writer writer) { long now = System.currentTimeMillis(); System.out.println("--Entering-- " + now); PrintWriter p = new PrintWriter (writer); p.write(this.FormattedString()); now = System.currentTimeMillis(); System.out.println("--Exiting-- " + now); } /* public void print(JspWriter out) throws java.io.IOException { print (new PrintWriter(out)); } */ @SuppressWarnings("deprecation") public static void main (String args[]) { NameAndAddress naa = new NameAndAddress(); naa.firstName = "Brian"; naa.middleName = "Matthew"; naa.lastName = "Kessler"; naa.address1 = "Tatra u. 15/b V/3"; naa.city = "Budapest"; naa.state = "Hungary"; naa.zip = "HU-1136"; System.out.println("\nTesting PrintWriter..."); PrintWriter p = null; try { p = new PrintWriter("d:/temp/pwriter_text.txt"); } catch (FileNotFoundException e) { System.err.print ("Can not create new PrintWriter: " + e); e.printStackTrace(); } naa.print(p); p.flush(); FileInputStream fis; DataInputStream dis; try { fis = new FileInputStream("d:/temp/pwriter_text.txt"); dis = new DataInputStream (fis); while (dis.available() != 0) { System.out.println(dis.readLine()); } dis.close(); } catch (Exception e) { System.err.println("File input error"); } System.out.println("\nTested PrintWriter..."); System.out.println("---------------------"); System.out.println("\nTesting JSPWriter..."); JspWriter j = null; naa.print(j); System.out.print("\nTested JSPWriter..."); System.out.println("---------------------"); System.out.println("\nTesting MockJspWriter"); MockJspWriter m = null; m = new MockJspWriter(255, true); naa.print(m); System.out.print(m.getContent()); System.out.println("\nTested MockJSPWriter..."); System.out.println("---------------------"); } } 

I expected the print () method to catch both JspWriter and PrintWriter.

Although this solution worked fine for PrintWriter, when I tried to run it as a console application, I get this output:

 Testing PrintWriter... --Entering-- --Exiting-- <PRE> Brian Matthew Kessler Tatra u. 15/b V/3 Budapest, Hungary HU-1136 </PRE> Tested PrintWriter... --------------------- Testing JSPWriter... --Entering-- Exception in thread "main" java.lang.NullPointerException at hu.flux.helper.NameAndAddress.print(NameAndAddress.java:46) at hu.flux.helper.NameAndAddress.main(NameAndAddress.java:101) 

I get another error, however, if I try to access the write (writer writer) from the JSP:

 HTTP Status 500 - type Exception report message description The server encountered an internal error () that prevented it from fulfilling this request. exception org.apache.jasper.JasperException: javax.servlet.ServletException: java.lang.NoSuchMethodError: hu.flux.helper.NameAndAddress.print(Ljavax/servlet/jsp/JspWriter;)V org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:492) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:407) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265) javax.servlet.http.HttpServlet.service(HttpServlet.java:722) root cause javax.servlet.ServletException: java.lang.NoSuchMethodError: hu.flux.helper.NameAndAddress.print(Ljavax/servlet/jsp/JspWriter;)V org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:898) org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:827) org.apache.jsp.Address_jsp._jspService(Address_jsp.java:92) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:68) javax.servlet.http.HttpServlet.service(HttpServlet.java:722) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:376) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265) javax.servlet.http.HttpServlet.service(HttpServlet.java:722) root cause java.lang.NoSuchMethodError: hu.flux.helper.NameAndAddress.print(Ljavax/servlet/jsp/JspWriter;)V org.apache.jsp.Address_jsp._jspService(Address_jsp.java:81) org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:68) javax.servlet.http.HttpServlet.service(HttpServlet.java:722) org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:376) org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:320) org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265) javax.servlet.http.HttpServlet.service(HttpServlet.java:722) note The full stack trace of the root cause is available in the Apache Tomcat/7.0.2 logs. Apache Tomcat/7.0.2 

When called from JSP, I can call the class with JspWriter running by adding this code:

 public void print(JspWriter out) throws java.io.IOException { print (new PrintWriter(out)); } 

However, when trying to use JspWriter from a console application (for testing - I don’t think anyone will ever need to use JspWriter in the console!), The above console error is moved to this function.

If printing (JspWriter out) can fix the problem for JSP, should the problem for console applications also be fixed?

Also, if JspWriter is a Writer object, should it not always be a Writer object, regardless of whether it is invoked from the console or JSP?

Answer 1

This exception indicates that your JSP code was not recompiled after changing print(JspWriter) to print(Object) , so it still tries to call print(JspWriter) and cannot find it.

To force recompilation, you can change the JSP page.

Answer 2

This is because the Java compiler is trying to find the PrintWriter.print method in the JspWriter object. Although it has a printing method, this method does not match because it is from a different class. Java does not support duck printing and is suitable for preventing it.

It is also considered bad practice to use exceptions in programming logic.

You need to do sthg as

  try { if (out instanceof PrintWriter) { ((PrintWriter) out).print(this.formattedString()); } else if (out instanceof JspWriter) { ((JspWriter) out).print(this.formattedString()); } else { throw new IllegalArgumentException("NameAndAddress.print expected ether a PrintWriter or a JspWriter but received a " + out.getClass().getName()); } catch (Exception ex) { System.err.println("\"out\" is not a printable type: " + ex); } 

BTW: Methods in Java must begin with a lowercase letter by convention.

Answer 3

What you posted should work, since both PrintWriter and JspWriter are subclasses of Writer (and, of course, both are subclasses of Object ). Something seems wrong with either your test code or with your environment.

Maybe you can try a simplified example and see if this works, and then create from there. I can suggest starting here:

 public class Test { public void print(Writer writer) throws IOException { if (writer == null) System.out.println("Null writer"); else { writer.write("hello"); writer.flush(); } } public static void main(String args[]) throws IOException { Test test = new Test(); System.out.print("Testing PrintWriter..."); PrintWriter p = new PrintWriter("d:/temp/pwriter_text.txt"); test.print(p); System.out.print("Tested PrintWriter..."); System.out.print("Testing JspWriter..."); JspWriter j = null; test.print(j); System.out.print("Tested JspWriter..."); } } 

This should compile and execute. The second time test.print() is JspWriter , the passed JspWriter will be null , but you should not receive a NoSuchMethodError . If this works, grab the code and test it from the servlet / JSP pages. Hope this helps you find the problem.

Answer 4

JspWriter is not a PrintWriter

You can wrap the original recording inside the printer as follows:

 if (out instance of Writer) { PrintWriter p = new PrintWriter((Writer) out)); p.print... } 

Answer 5

Well, you start your method by adding PrintWriter , so maybe jvm has optimized this method for you. Since JspWriter not a subclass of PrintWriter , it is best to write two methods:

 public void print(JspWriter out) { if (out == null) return; try { out.print(this.FormattedString()); } Except (IOException e) { // handle error } } public void print(PrintWriter out) { if (out == null) return; try { out.print(this.FormattedString()); } Except (IOException e) { // handle error } } 

If only JspWriter and PrintWriter had a common interface ... sigh.

Answer 6

Your print () translates the object into PrintWriter. But when you pass in a JspWriter that is not a PrintWriter, the failure is executed.

However, PrintWriter and JspWriter both come from Writer. Can you change your print() method to accept Writer instead of Object, and then use the Writer.write () method in print() ? This is common to both classes.

It:

 public void print(Writer writer) { try { writer.write(this.FormattedString()); } catch (IOException e) { // log something... } }