java - 接收 java.lang.Object 作为输入的方法不应该也接收 javax.servlet.jsp.JspWriter 作为输入吗？

Question

我想 consolidate two functions .

在找到可行的解决方案后，我决定进一步研究代码，并得出以下结论:

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("---------------------");
    }
}

我预计 print() 方法会捕获 JspWriter 和 PrintWriter。

虽然此解决方案适用于 PrintWriter，但当我尝试将其作为控制台应用程序运行时，我得到了以下输出:

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，如果我尝试从 JSP 访问 print(Writer writer)，我会得到一个不同的错误:

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

当从 JSP 调用时，我可以通过添加以下代码来调用具有 JspWriter 工作的类:

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 时(为了测试——我认为任何人都不需要在控制台中使用 JspWriter!)，上面的控制台错误被移至此函数。

如果 print(JspWriter out) 可以解决 JSP 的问题，难道它不应该也解决控制台应用程序的问题吗？

此外，如果 JspWriter 是一个 Writer 对象，它不应该总是一个 Writer 对象，无论它是从控制台还是从 JSP 调用的？

Answer 1

此异常表示在将 print(JspWriter) 更改为 print(Object) 后，您的 JSP 代码尚未重新编译，因此它仍会尝试调用 print(JspWriter) 找不到它。

为了强制重新编译，您可以修改您的 JSP 页面。