我想consolidate two functions。
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：
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。
尽管此解决方案对于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：
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），则会收到另一个错误：
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，可以通过添加以下代码来使用JspWriter调用该类：
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（进行测试-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函数。
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？
而且，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？
最佳答案
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，因此它仍然尝试调用print(JspWriter)并找不到它。
为了强制重新编译，您可以修改JSP页面。