接收java.lang.Object作为输入的方法是否也应该接收javax.servlet.jsp.JspWriter作为输入? [英] Shouldn't a method that receives java.lang.Object as input also receive javax.servlet.jsp.JspWriter as input?
问题描述
我想在找到可行的解决方案之后，我决定进一步研究代码，并提出以下建议:
After getting a viable solution, I decided to play with the code a bit further, and came up with this:
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("---------------------");
}
}
我希望print()方法可以同时捕获JspWriter和PrintWriter.
I expected that the print() method would catch both JspWriter and PrintWriter.
虽然此解决方案对于PrintWriter效果很好，但是当我尝试将其作为控制台应用程序运行时，却得到以下输出:
While this solution worked fine for PrintWriter, when I tried to run this 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)
但是，如果尝试从JSP访问print(Writer writer)，则会遇到另一个错误:
I get a different error, however, if I try to access print(Writer writer) from a 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
从JSP调用时，我可以通过添加以下代码来使JspWriter对该类进行调用:
When calling from the JSP, I can make a call to the class with JspWriter work by adding this code:
public void print(JspWriter out) throws java.io.IOException
{ print (new PrintWriter(out)); }
但是，当尝试从控制台应用程序使用JspWriter(用于测试-我认为没有人会在控制台中使用JspWriter！)时，上述控制台错误已移至该功能.
However, when attempting to use JspWriter from a console application (for testing -- I don't think anyone would ever need to use JspWriter in the console!), the above console error is moved to this function.
如果print(JspWriter out)可以解决JSP的问题，那么它是否也可以解决控制台应用程序的问题?
If print(JspWriter out) can fix the problem for JSPs, shouldn't it also fix the problem for console apps?
此外，如果JspWriter是Writer对象，则无论它是从控制台还是JSP调用，它都不应该始终是Writer对象吗?
Moreover, if JspWriter is a Writer object, shouldn't it always be a Writer object, regardless whether it is called from the console or a JSP?
推荐答案
此异常表示将print(JspWriter)更改为print(Object)后，尚未重新编译您的JSP代码，因此它仍尝试调用print(JspWriter)和找不到它.
This exception says that your JSP code haven't been recompiled after you changed print(JspWriter) to print(Object), so it still tries to call print(JspWriter) and can't find it.
为了强制重新编译，您可以修改JSP页面.
In order to force a recompilation you may modify your JSP page.
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