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          version 10 
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          version 1:
          

          
At line 2 added 257 lines.

Inspired by <a href="http://www.raibledesigns.com/page/rd?anchor=how_do_you_manage_your">this post</a>, I wrote a tag library to expose the fields of my Contants.java class to my JSPs.  It allows a user to specify a single variable using:

{{{
<appfuse:constants var="USER_KEY"/>
}}}

Or all variables:

{{{
<appfuse:constants/>
}}}

By default, it exposes the values from the Contants class imported into the tag library, but also allows a className variable to specify a different class.  The main reason I wrote this was to prove it was possible.  The second reason was to get around importing my Contants class (and using &lt;%=Contants.VARNAME%&gt;).  With this tag, both of the following work:

{{{Scriptlet: <%=VARNAME%>, JSTL: <c:out value="${VARNAME}"/>}}}

The only thing it gives you over the import/scriptlet way is to expose the attribute to different scopes - i.e. page for JSTL.  After writing it, I think it's a fairly useless tag library - I don't know if I'll ever use it, but maybe someone else will find it useful.

;:''BTW, you need to use it on the JSP you plan to use it in a scriptlet and you can't wrap it with oscache's &lt;cache&gt; tags.''

!Files Needed for Tag Library
* [1] ConstantsTag.java
* [2] ConstantsTei.java - exposes variables as attributes
----
!!ConstantsTag.java [#1]
[{Java2HtmlPlugin 

package org.appfuse.webapp.taglib;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.TagSupport;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.struts.taglib.TagUtils;
import org.appfuse.common.Constants;


/**
 * <p>This class is designed to put all the public variables in a class to a
 * specified scope - designed for exposing a Constants class to Tag
 * Libraries.</p>
 *
 * <p>It is designed to be used as follows:
 * <pre>&lt;tag:constants /&gt;</pre>
 * </p>
 *
 * <p>Optional values are "className" (fully qualified) and "scope".</p>
 *
 * <p>
 * <a href="BaseAction.java.html"><i>View Source</i></a>
 * </p>
 *
 * @author <a href="mailto:[email protected]">Matt Raible</a>
 * @version $Revision: 1.1 $ $Date: 2003/12/31 13:59:32 $
 *
 * @jsp.tag name="constants" bodycontent="empty"
 *  tei-class="us.co.adams.apptracker.webapp.taglib.ConstantsTei"
 */
public class ConstantsTag extends TagSupport {
    private Log log = LogFactory.getLog(ConstantsTag.class);

    /**
     * The class to expose the variables from.
     */
    public String clazz = Constants.class.getName();

    /**
     * The scope to be put the variable in.
     */
    protected String scope = null;

    /**
     * The single variable to expose.
     */
    protected String var = null;

    public int doStartTag() throws JspException {
        // Using reflection, get the available field names in the class
        Class c = null;
        int toScope = PageContext.PAGE_SCOPE;

        if (scope != null) {
            // default to pageScope
            toScope = TagUtils.getInstance().getScope(scope);
        }

        try {
            c = Class.forName(clazz);
        } catch (ClassNotFoundException cnf) {
            log.error("ClassNotFound - maybe a typo?");
            throw new JspException(cnf.getMessage());
        }

        try {
            // if var is null, expose all variables
            if (var == null) {
                Field[] fields = c.getDeclaredFields();

                AccessibleObject.setAccessible(fields, true);

                for (int i = 0; i < fields.length; i++) {
                    /*if (log.isDebugEnabled()) {
                       log.debug("putting '" + fields[i].getName() + "=" +
                                 fields[i].get(this) + "' into " + scope +
                                 " scope");
                       }*/
                    pageContext.setAttribute(fields[i].getName(),
                                             fields[i].get(this), toScope);
                }
            } else {
                try {
                    String value = (String) c.getField(var).get(this);
                    pageContext.setAttribute(c.getField(var).getName(), value,
                                             toScope);
                } catch (NoSuchFieldException nsf) {
                    log.error(nsf.getMessage());
                    throw new JspException(nsf);
                }
            }
        } catch (IllegalAccessException iae) {
            log.error("Illegal Access Exception - maybe a classloader issue?");
            throw new JspException(iae);
        }

        // Continue processing this page
        return (SKIP_BODY);
    }

    /**
     * @jsp.attribute
     */
    public void setClassName(String clazz) {
        this.clazz = clazz;
    }

    public String getClassName() {
        return this.clazz;
    }

    /**
     * @jsp.attribute
     */
    public void setScope(String scope) {
        this.scope = scope;
    }

    public String getScope() {
        return (this.scope);
    }

    /**
     * @jsp.attribute
     */
    public void setVar(String var) {
        this.var = var;
    }

    public String getVar() {
        return (this.var);
    }

    /**
     * Release all allocated resources.
     */
    public void release() {
        super.release();
        clazz = null;
        scope = Constants.class.getName();
    }
}

}]

----
!!ConstantsTei.java [#2]

[{Java2HtmlPlugin 

package org.appfuse.webapp.taglib;

import java.lang.reflect.AccessibleObject;
import java.lang.reflect.Field;

import java.util.ArrayList;
import java.util.List;

import javax.servlet.jsp.tagext.TagData;
import javax.servlet.jsp.tagext.TagExtraInfo;
import javax.servlet.jsp.tagext.VariableInfo;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import org.appfuse.common.Constants;


/**
 * Implementation of <code>TagExtraInfo</code> for the <b>constants</b>
 * tag, identifying the scripting object(s) to be made visible.
 *
 * @author Matt Raible
 * @version $Revision: 1.1 $ $Date: 2003/12/31 13:59:32 $
 */
public class ConstantsTei extends TagExtraInfo {
    private Log log = LogFactory.getLog(ConstantsTei.class);

    /**
     * Return information about the scripting variables to be created.
     */
    public VariableInfo[] getVariableInfo(TagData data) {
        // loop through and expose all attributes
        List vars = new ArrayList();

        try {
            String clazz = data.getAttributeString("className");

            if (clazz == null) {
                clazz = Constants.class.getName();
            }

            Class c = Class.forName(clazz);

            // if no var specified, get all
            if (data.getAttributeString("var") == null) {
                Field[] fields = c.getDeclaredFields();

                AccessibleObject.setAccessible(fields, true);

                for (int i = 0; i < fields.length; i++) {
                    vars.add(new VariableInfo(fields[i].getName(),
                                              "java.lang.String", true,
                                              VariableInfo.AT_END));
                }
            } else {
                String var = data.getAttributeString("var");
                vars.add(new VariableInfo(c.getField(var).getName(),
                                          "java.lang.String", true,
                                          VariableInfo.AT_END));
            }
        } catch (Exception cnf) {
            log.error(cnf.getMessage());
            cnf.printStackTrace();
        }

        return (VariableInfo[]) vars.toArray(new VariableInfo[] {  });
    }
}

}]

Also see [my blog post|http://www.raibledesigns.com/page/rd?anchor=useless_tag_library].


          

      

      

      
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-ConstantsTag
+    Search Wiki:
 At line 2 added 257 lines.
+Inspired by <a href="http://www.raibledesigns.com/page/rd?anchor=how_do_you_manage_your">this post</a>, I wrote a tag library to expose the fields of my Contants.java class to my JSPs.  It allows a user to specify a single variable using:
+{{{
+<appfuse:constants var="USER_KEY"/>
+}}}
+Or all variables:
+{{{
+<appfuse:constants/>
+}}}
+By default, it exposes the values from the Contants class imported into the tag library, but also allows a className variable to specify a different class.  The main reason I wrote this was to prove it was possible.  The second reason was to get around importing my Contants class (and using &lt;%=Contants.VARNAME%&gt;).  With this tag, both of the following work:
+{{{Scriptlet: <%=VARNAME%>, JSTL: <c:out value="${VARNAME}"/>}}}
+The only thing it gives you over the import/scriptlet way is to expose the attribute to different scopes - i.e. page for JSTL.  After writing it, I think it's a fairly useless tag library - I don't know if I'll ever use it, but maybe someone else will find it useful.
+;:''BTW, you need to use it on the JSP you plan to use it in a scriptlet and you can't wrap it with oscache's &lt;cache&gt; tags.''
+!Files Needed for Tag Library
+* [1] ConstantsTag.java
+* [2] ConstantsTei.java - exposes variables as attributes
+----
+!!ConstantsTag.java [#1]
+[{Java2HtmlPlugin
+package org.appfuse.webapp.taglib;
+import java.lang.reflect.AccessibleObject;
+import java.lang.reflect.Field;
+import javax.servlet.jsp.JspException;
+import javax.servlet.jsp.PageContext;
+import javax.servlet.jsp.tagext.TagSupport;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.struts.taglib.TagUtils;
+import org.appfuse.common.Constants;
+/**
+ * <p>This class is designed to put all the public variables in a class to a
+ * specified scope - designed for exposing a Constants class to Tag
+ * Libraries.</p>
+ *
+ * <p>It is designed to be used as follows:
+ * <pre>&lt;tag:constants /&gt;</pre>
+ * </p>
+ *
+ * <p>Optional values are "className" (fully qualified) and "scope".</p>
+ *
+ * <p>
+ * <a href="BaseAction.java.html"><i>View Source</i></a>
+ * </p>
+ *
+ * @author <a href="mailto:[email protected]">Matt Raible</a>
+ * @version $Revision: 1.1 $ $Date: 2003/12/31 13:59:32 $
+ *
+ * @jsp.tag name="constants" bodycontent="empty"
+ *  tei-class="us.co.adams.apptracker.webapp.taglib.ConstantsTei"
+ */
+public class ConstantsTag extends TagSupport {
+    private Log log = LogFactory.getLog(ConstantsTag.class);
+    /**
+     * The class to expose the variables from.
+     */
+    public String clazz = Constants.class.getName();
+    /**
+     * The scope to be put the variable in.
+     */
+    protected String scope = null;
+    /**
+     * The single variable to expose.
+     */
+    protected String var = null;
+    public int doStartTag() throws JspException {
+        // Using reflection, get the available field names in the class
+        Class c = null;
+        int toScope = PageContext.PAGE_SCOPE;
+        if (scope != null) {
+            // default to pageScope
+            toScope = TagUtils.getInstance().getScope(scope);
+        }
+        try {
+            c = Class.forName(clazz);
+        } catch (ClassNotFoundException cnf) {
+            log.error("ClassNotFound - maybe a typo?");
+            throw new JspException(cnf.getMessage());
+        }
+        try {
+            // if var is null, expose all variables
+            if (var == null) {
+                Field[] fields = c.getDeclaredFields();
+                AccessibleObject.setAccessible(fields, true);
+                for (int i = 0; i < fields.length; i++) {
+                    /*if (log.isDebugEnabled()) {
+                       log.debug("putting '" + fields[i].getName() + "=" +
+                                 fields[i].get(this) + "' into " + scope +
+                                 " scope");
+                       }*/
+                    pageContext.setAttribute(fields[i].getName(),
+                                             fields[i].get(this), toScope);
+                }
+            } else {
+                try {
+                    String value = (String) c.getField(var).get(this);
+                    pageContext.setAttribute(c.getField(var).getName(), value,
+                                             toScope);
+                } catch (NoSuchFieldException nsf) {
+                    log.error(nsf.getMessage());
+                    throw new JspException(nsf);
+                }
+            }
+        } catch (IllegalAccessException iae) {
+            log.error("Illegal Access Exception - maybe a classloader issue?");
+            throw new JspException(iae);
+        }
+        // Continue processing this page
+        return (SKIP_BODY);
+    }
+    /**
+     * @jsp.attribute
+     */
+    public void setClassName(String clazz) {
+        this.clazz = clazz;
+    }
+    public String getClassName() {
+        return this.clazz;
+    }
+    /**
+     * @jsp.attribute
+     */
+    public void setScope(String scope) {
+        this.scope = scope;
+    }
+    public String getScope() {
+        return (this.scope);
+    }
+    /**
+     * @jsp.attribute
+     */
+    public void setVar(String var) {
+        this.var = var;
+    }
+    public String getVar() {
+        return (this.var);
+    }
+    /**
+     * Release all allocated resources.
+     */
+    public void release() {
+        super.release();
+        clazz = null;
+        scope = Constants.class.getName();
+    }
+}
+}]
+----
+!!ConstantsTei.java [#2]
+[{Java2HtmlPlugin
+package org.appfuse.webapp.taglib;
+import java.lang.reflect.AccessibleObject;
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+import java.util.List;
+import javax.servlet.jsp.tagext.TagData;
+import javax.servlet.jsp.tagext.TagExtraInfo;
+import javax.servlet.jsp.tagext.VariableInfo;
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.appfuse.common.Constants;
+/**
+ * Implementation of <code>TagExtraInfo</code> for the <b>constants</b>
+ * tag, identifying the scripting object(s) to be made visible.
+ *
+ * @author Matt Raible
+ * @version $Revision: 1.1 $ $Date: 2003/12/31 13:59:32 $
+ */
+public class ConstantsTei extends TagExtraInfo {
+    private Log log = LogFactory.getLog(ConstantsTei.class);
+    /**
+     * Return information about the scripting variables to be created.
+     */
+    public VariableInfo[] getVariableInfo(TagData data) {
+        // loop through and expose all attributes
+        List vars = new ArrayList();
+        try {
+            String clazz = data.getAttributeString("className");
+            if (clazz == null) {
+                clazz = Constants.class.getName();
+            }
+            Class c = Class.forName(clazz);
+            // if no var specified, get all
+            if (data.getAttributeString("var") == null) {
+                Field[] fields = c.getDeclaredFields();
+                AccessibleObject.setAccessible(fields, true);
+                for (int i = 0; i < fields.length; i++) {
+                    vars.add(new VariableInfo(fields[i].getName(),
+                                              "java.lang.String", true,
+                                              VariableInfo.AT_END));
+                }
+            } else {
+                String var = data.getAttributeString("var");
+                vars.add(new VariableInfo(c.getField(var).getName(),
+                                          "java.lang.String", true,
+                                          VariableInfo.AT_END));
+            }
+        } catch (Exception cnf) {
+            log.error(cnf.getMessage());
+            cnf.printStackTrace();
+        }
+        return (VariableInfo[]) vars.toArray(new VariableInfo[] {  });
+    }
+}
+}]
+Also see [my blog post|http://www.raibledesigns.com/page/rd?anchor=useless_tag_library].