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"Writing Custom JSP Tag Libraries"
Vol. 5, Issue 10, p. 36
Listing 1
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
import java.io.*;
public class SimpleTag extends TagSupport {
public int doStartTag() {
try {
JspWriter out = pageContext.getOut();
out.println("Java Developers Journal");
} catch (IOException ioe) {
System.out.println("Error writing to out: " + ioe);
}
return(SKIP_BODY);
}
}
Listing 2
public class SimpleTag extends TagSupport {
public int doStartTag() {
try {
JspWriter out = pageContext.getOut();
out.println("<font face=geneva size=8 color=blue>");
} catch (IOException ioe) {
System.out.println("Error writing to out: " + ioe);
}
return(EVAL_BODY_INCLUDE);
}
public int doEndTag() {
try {
JspWriter out = pageContext.getOut();
out.println("</font>");
} catch (IOException ioe) {
System.out.println("Error writing to out: " + ioe);
}
return(EVAL_PAGE);
}
}
Listing 3
<%@ taglib uri="jdj.tld" prefix="jdj" %>
<html>
<body>
<jdj:simple>
Custom JSP Tags!
</jdj:simple>
</body>
</html>
Listing 4
private String color;
//Set via the tag attribute fontcolor
public void setFontcolor(String value ) {
color = value;
}
public int doStartTag() {
try {
JspWriter out = pageContext.getOut();
out.println("<font face=geneva size=8 color="+color+">");
} catch (IOException ioe) {
System.out.println("Error writing to out: " + ioe);
}
return(EVAL_BODY_INCLUDE);
}
Listing 5
package com.jdj;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
import java.io.*;
public class UpperCaseTag extends BodyTagSupport {
public int doAfterBody() {
try {
BodyContent body = getBodyContent();
JspWriter out = body.getEnclosingWriter();
out.print( body.getString().toUpperCase() );
} catch (IOException ioe) {
System.out.println("Error writing to out: " + ioe);
}
return(SKIP_BODY);
}
}
Listing 6
package com.jdj;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
import java.io.*;
import java.sql.*;
public class QueryTag extends BodyTagSupport {
private ResultSet rs = null;
private Statement st = null;
private Connection con = null;
//Attributes
private String connectString;
private String driverClass;
private String sql;
private String user;
private String password;
public int doStartTag() {
loadData();
return( EVAL_BODY_TAG );
}
public int doEndTag() {
closeConnections();
return( EVAL_PAGE );
}
private void closeConnections() {
try { rs.close(); } catch ( Exception e ) {};
try { st.close(); } catch ( Exception e ) {};
try { con.close(); } catch ( Exception e ) {};
}
private void loadData() {
try {
Class.forName( driverClass );
con = DriverManager.getConnection( connectString, user, password );
st = con.createStatement();
rs = st.executeQuery( sql );
rs.next();
} catch ( Exception e ) {
System.out.println("Error loading data: " + e );
}
}
public int doAfterBody() {
try {
BodyContent body = getBodyContent();
JspWriter out = body.getEnclosingWriter();
out.println( body.getString() );
//Clear the body (in case we loop again)
body.clearBody();
if ( rs.next() ) {
//There is another row so evaluate the body again
return( EVAL_BODY_TAG );
} else {
//Last row so don't evaluate the body anymore
return( SKIP_BODY );
}
} catch ( Exception e ) {
System.out.println( "Error in doAfterBody: " + e );
return( SKIP_BODY );
}
}
//This is the method our nested tags will call to get the
//value of a particular column in the current row
public String getDataValue( String columnName ) throws SQLException {
return( rs.getString( columnName ) );
}
public void setConnectString( String value ) {
connectString = value;
}
public void setDriver( String value ) {
driverClass = value;
}
public void setQuery( String value ) {
sql = value;
}
public void setUser( String value ) {
user = value;
}
public void setPass( String value ) {
password = value;
}
}
Listing 7
package com.jdj;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
import java.util.*;
import java.io.*;
public class DataValueTag extends TagSupport {
//Attributes
private String columnName = "";
public DataValueTag() {
}
public int doStartTag() {
try {
JspWriter out = pageContext.getOut();
//Now try to get the parent
QueryTag qt = (QueryTag)findAncestorWithClass(this, QueryTag.class);
if ( qt == null ) {
out.print( "Must be enclosed in a query tag!");
} else {
try {
String val = qt.getDataValue( columnName );
out.print( val );
} catch ( Exception e ) {
System.out.println(" An error occurred in DataValueTag " + e );
out.println("An error occurred: " + e );
}
}
} catch ( Exception ioe ) {
System.out.println( "Error in doStarTag" + ioe );
}
return( SKIP_BODY );
}
public void setColname( String value ) {
columnName = value;
}
}
Listing 8
<tag>
<name>query</name>
<tagclass>com.jdj.QueryTag</tagclass>
<bodycontent>JSP</bodycontent>
<attribute>
<name>sql</name>
<required>true</required>
</attribute>
<attribute>
<name>driver</name>
<required>false</required>
</attribute>
<attribute>
<name>connectString</name>
<required>false</required>
</attribute>
<attribute>
<name>user</name>
<required>true</required>
</attribute>
<attribute>
<name>pass</name>
<required>true</required>
</attribute>
</tag>
<tag>
<name>data_value</name>
<tagclass>com.jdj.DataValueTag</tagclass>
<bodycontent>EMPTY</bodycontent>
<attribute>
<name>colname</name>
<required>true</required>
</attribute>
</tag>
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Copyright © 2004 SYS-CON Media, Inc.
E-mail: info@sys-con.com
Java and Java-based marks are trademarks or registered trademarks of Sun Microsystems, Inc. in the United States and other countries. SYS-CON Publications, Inc. is independent of Sun Microsystems, Inc.
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