EscapeHtmlTag.java

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 * Copyright 2004 The Apache Software Foundation
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 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
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package demo.taglib;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspTagException;
import javax.servlet.jsp.tagext.BodyTagSupport;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.StringReader;
import java.io.Writer;

/**
 * <p>Tag handler for <escapeHtml>
 *
 * @author Pierre Delisle
 * @version $Revision: 1.5 $ $Date: 2007/04/27 22:00:25 $
 */
public class EscapeHtmlTag extends BodyTagSupport {

    //*********************************************************************
    // Instance variables

    private Reader reader;
    private Writer writer;

    //*********************************************************************
    // Constructors

    public EscapeHtmlTag() {
        super();
        init();
    }


    private void init() {
        reader = null;
        writer = null;
    }

    //*********************************************************************
    // Tag's properties

    /** Tag's 'reader' attribute */
    public void setReader(Reader reader) {
        this.reader = reader;
    }


    /** Tag's 'writer' attribute */
    public void setWriter(Writer writer) {
        this.writer = writer;
    }

    //*********************************************************************
    // TagSupport methods

    public int doEndTag() throws JspException {
        Reader in;
        Writer out;

        if (reader == null) {
            String bcs = getBodyContent().getString().trim();
            if (bcs == null || bcs.equals("")) {
                throw new JspTagException("In <escapeHtml>, 'reader' " +
                                          "not specified and no non-whitespace content inside the tag.");
            }
            in = castToReader(bcs);
        } else {
            in = reader;
        }

        if (writer == null) {
            out = pageContext.getOut();
        } else {
            out = writer;
        }

        transform(in, out);
        return EVAL_PAGE;
    }


    /** Releases any resources we may have (or inherit) */
    public void release() {
        super.release();
        init();
    }

    //*********************************************************************
    // Tag's scific behavior methods

    /** Transform */
    public void transform(Reader reader, Writer writer)
          throws JspException {
        int c;
        try {
            writer.write("<pre>");
            while ((c = reader.read()) != -1) {
                if (c == '<') {
                    writer.write("<");
                } else if (c == '>') {
                    writer.write(">");
                } else {
                    writer.write(c);
                }
            }
            writer.write("</pre>");
        } catch (IOException ex) {
            throw new JspException("EscapeHtml: " +
                                   "error copying chars", ex);
        }
    }

    //*********************************************************************
    // Utility methods   


    public static Reader castToReader(Object obj) throws JspException {
        if (obj instanceof InputStream) {
            return new InputStreamReader((InputStream) obj);
        } else if (obj instanceof Reader) {
            return (Reader) obj;
        } else if (obj instanceof String) {
            return new StringReader((String) obj);
        }
        throw new JspException("Invalid type '" + obj.getClass().getName() +
                               "' for castToReader()");
    }


    public static Writer castToWriter(Object obj) throws JspException {
        if (obj instanceof OutputStream) {
            return new OutputStreamWriter((OutputStream) obj);
        } else if (obj instanceof Writer) {
            return (Writer) obj;
            /*@@@
        } else if (obj instanceof String) {
            return new StringWriter();
             */
        }
        throw new JspException("Invalid type '" + obj.getClass().getName() +
                               "' for castToWriter()");
    }

}