小编典典

JSP:对jsp使用“ out”(jspWriter)的委托包括更改表达式的行为

jsp

比如说,有一个MyJSPWriter扩展JspWriter和实现所有抽象方法的类。print(String )经过修改后添加了一些特殊的行为,因此所有作为字符串的表达式都将得到不同的对待(也许我可以将其用于某些特殊的编码等这样-这是一个简化的示例):

package com.myproject.base;

import java.io.IOException;
import javax.servlet.jsp.JspWriter;

public class MyJSPWriter extends JspWriter{

    JspWriter out = null;

    public MyJSPWriter(JspWriter out) {
        super(0, true);
        this.out = out;
    }


    @Override
    public String toString() {
        return out.toString();
    }

    @Override
    public void clear() throws IOException {
        out.clear();
    }

    @Override
    public void clearBuffer() throws IOException {
        out.clearBuffer();
    }

    @Override
    public void close() throws IOException {
        out.close();
    }

    @Override
    public void flush() throws IOException {
        out.flush();
    }

    @Override
    public int getRemaining() {
        return out.getRemaining();
    }

    @Override
    public void newLine() throws IOException {
        out.newLine();
    }

    @Override
    public void print(boolean b) throws IOException {
        out.print(b);
    }

    @Override
    public void print(char c) throws IOException {
        out.print(c);
    }

    @Override
    public void print(int i) throws IOException {
        out.print(i);
    }

    @Override
    public void print(long l) throws IOException {
        out.print(l);
    }

    @Override
    public void print(float f) throws IOException {
        out.print(f);
    }

    @Override
    public void print(double d) throws IOException {
        out.print(d);
    }

    @Override
    public void print(char[] s) throws IOException {
        out.print(s);
    }

    @Override
    public void print(String s) throws IOException {
        out.print("Processed String: " + s);
    }

    @Override
    public void print(Object obj) throws IOException {
        out.print(obj);
    }

    @Override
    public void println() throws IOException {
        out.println();
    }

    @Override
    public void println(boolean x) throws IOException {
        out.println(x);
    }

    @Override
    public void println(char x) throws IOException {
        out.println(x);
    }

    @Override
    public void println(int x) throws IOException {
        out.println(x);
    }

    @Override
    public void println(long x) throws IOException {
        out.println(x);
    }

    @Override
    public void println(float x) throws IOException {
        out.println(x);
    }

    @Override
    public void println(double x) throws IOException {
        out.println(x);
    }

    @Override
    public void println(char[] x) throws IOException {
           out.println(x);
    }

    @Override
    public void println(String x) throws IOException {
           out.println(x);
    }

    @Override
    public void println(Object x) throws IOException {
           out.println(x);
    }

    @Override
    public void write(char[] cbuf, int off, int len) throws IOException {
        out.write(cbuf, off, len);
    }


}

我有jsp(说Main.jsp),它看起来像这样:

<%@page import="com.myproject.base"%>
<% out = new MyJSPWriter(out); %>

<%= " Hello World" %>

因此,在我的输出中,它将显示为

Processed String: Hello World

现在,如果我有更多的jsp:includes,并且可能在每个其中都包含includes。例如:

Main.jsp

<%@page import="com.myproject.base"%>
<% out = new MyJSPWriter(out); %>

<%= " Hello World" %>
<jsp:include page="Sub1.jsp"></jsp:include>
<jsp:include page="Sub2.jsp"></jsp:include>

Sub1.jsp

<%= " Hello World from sub1.jsp" %>

Sub2.jsp

<%= " Hello World from sub2.jsp" %>
<jsp:include page="Sub3.jsp"></jsp:include>

等等…

但是所有子jsp都有out自己的对象… :-(

我们如何在不添加的情况下为所有包含的jsps带来相同的行为

<% out = new MyJSPWriter(out); %>

在这些文件的每个文件中(因为我正在尝试在旧版应用程序中使用它)?

我还有其他方法可以解决吗?

附加信息: 当我们查看jsp的生成的.java文件时,这就是部分代码的样子

public void _jspService(HttpServletRequest request, HttpServletResponse response)
        throws java.io.IOException, ServletException {

    PageContext pageContext = null;
    HttpSession session = null;
    ServletContext application = null;
    ServletConfig config = null;
    JspWriter out = null;
    Object page = this;
    JspWriter _jspx_out = null;
    PageContext _jspx_page_context = null;


    try {
      response.setContentType("text/html");
      pageContext = _jspxFactory.getPageContext(this, request, response,
                null, true, 8192, true);
      _jspx_page_context = pageContext;
      application = pageContext.getServletContext();
      config = pageContext.getServletConfig();
      session = pageContext.getSession();
      out = pageContext.getOut();
      _jspx_out = out;
      out = new MyJSPWriter(out);
      // and so on writing content ....

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2020-06-08

共1个答案

小编典典

如果您查看生成的jsp类的顶部,您将看到以下行

 private static final JspFactory _jspxFactory = JspFactory.getDefaultFactory();

现在,自定义out对象的一种可能解决方案是具有自定义实现JspFactory

脚步

创建一个自定义的JspFactory实现

public class MyJspFactory extends JspFactory {
    private static JspFactory _myFactory = null;
    public MyJspFactory(JspFactory factory) {
        _myFactory = factory;
    } 
   //All abstract methods which looks up _myFactory and does the same thing

   public PageContext getPageContext(Servlet servlet, ServletRequest request, ServletResponse response, String errorPageURL, boolean needsSession, int bufferSize, boolean autoflush) {
        PageContext myCtxt = _myFactory.getPageContext(....)
        //Create a customPageContext and wrap myCtxt in it and return
   }
}

创建一个CutsomPageContext类

public class MyPageContext extends PageContext {
    private PageContext _ctxt = null;

    public void setPageContext(PageContext ctxt) {
        _ctxt = ctxt;
    }

    //Implement all abstract methods using _ctxt object

    @override
    public  JspWriter getOut() {
        JspWriter _out = _ctxt.getOut();

        //Wrap _out object using MyJSPWriter as mentioned in question and return back;

    }
}

现在,在servlet的初始化过程中,添加以下行

JspFactory newFactory = new MyJspFactory(JspFactory.getDefaultFactory());
JspFactory.setDefaultFactory(newFactory);

我还没有尝试过。但从概念上讲,它应该起作用。如果您可以通过此方法实现目标,请告诉我们。

祝好运!

2020-06-08