Class RenderTool

java.lang.Object

org.apache.velocity.tools.generic.SafeConfig

org.apache.velocity.tools.generic.RenderTool

@DefaultKey("render")
@InvalidScope("session")
public class RenderTool
extends SafeConfig

This tool exposes methods to evaluate the given strings as VTL (Velocity Template Language) using either a pre-configured context or one you provide directly.

Example of eval():
     Input
     -----
     #set( $list = [1,2,3] )
     #set( $object = '$list' )
     #set( $method = 'size()' )
     $render.eval("${object}.$method")

     Output
     ------
     3

Example of recurse():
     Input
     -----
     #macro( say_hi )hello world!#end
     #set( $foo = '#say_hi()' )
     #set( $bar = '$foo' )
     $render.recurse($bar)

     Output
     ------
     hello world!


Toolbox configuration:
<tools>
  <toolbox scope="request">
    <tool class="org.apache.velocity.tools.generic.RenderTool">
      <property name="parseDepth" type="number" value="10"/>
    </tool>
  </toolbox>
</tools>

Ok, so these examples are really lame. But, it seems like someone out there is always asking how to do stuff like this and we always tell them to write a tool. Now we can just tell them to use this tool.

This tool may be used in any scope, however, the context provided for the eval(String) and recurse(String) methods will only be current if the tool is request scoped. If application or session scoped, then the context will be the same one set at the time of the tool's first use. In such a case, each call to eval(String) or recurse(String) will by default create a new Context that wraps the configured one to prevent modifications to the configured Context (concurrent or otherwise). If you wish to risk it and accrete changes then you can relax the thread-safety by setting the 'forceThreadSafe' property to 'false'.

Of course none of the previous paragraph likely applies if you are not using the core tool management facilities or if you stick to the eval(Context,String) and recurse(Context,String) methods. :)

This tool by default will catch and log any exceptions thrown during rendering and instead return null in such cases. It also limits recursion, by default, to 20 cycles, to prevent infinite loops. Both settings may be configured to behave otherwise.

Version:

$Revision$ $Date$

Author:

Nathan Bubna

Field Summary

Fields

Modifier and Type	Field	Description
static final int	DEFAULT_PARSE_DEPTH	The maximum number of loops allowed when recursing.
static final String	KEY_CATCH_EXCEPTIONS	Deprecated.
static final String	KEY_FORCE_THREAD_SAFE
static final String	KEY_PARSE_DEPTH	Deprecated.

Fields inherited from class SafeConfig

LOCK_CONFIG_KEY, log, LOGGER_NAME_KEY, SAFE_MODE_KEY, USE_CLASS_LOGGER_KEY

Constructor Summary

Constructors

Constructor	Description
RenderTool()

Method Summary

Modifier and Type	Method	Description
protected void	configure(ValueParser parser)	Looks for deprecated parse depth and catch.exceptions properties, as well as any 'forceThreadSafe' setting.
String	eval(String vtl)	Evaluates a String containing VTL using the context passed to the setVelocityContext(Context) method.
String	eval(org.apache.velocity.context.Context ctx, String vtl)	Evaluates a String containing VTL using the current context, and returns the result as a String.
boolean	getCatchExceptions()	Returns true if this render() and eval() methods will catch exceptions thrown during rendering.
int	getParseDepth()	Get the maximum number of loops allowed when recursing.
protected String	internalEval(org.apache.velocity.context.Context ctx, String vtl)
protected String	internalRecurse(org.apache.velocity.context.Context ctx, String vtl, int count)
String	recurse(String vtl)	Recursively evaluates a String containing VTL using the current context, and returns the result as a String.
String	recurse(org.apache.velocity.context.Context ctx, String vtl)	Recursively evaluates a String containing VTL using the current context, and returns the result as a String.
void	setCatchExceptions(boolean catchExceptions)	Sets whether or not the render() and eval() methods should catch exceptions during their execution or not.
void	setParseDepth(int depth)	Set the maximum number of loops allowed when recursing.
void	setVelocityContext(org.apache.velocity.context.Context context)	Sets the Context to be used by the eval(String) and recurse(String) methods.
void	setVelocityEngine(org.apache.velocity.app.VelocityEngine ve)	Allow user to specify a VelocityEngine to be used in place of the Velocity singleton.

Methods inherited from class SafeConfig

configure, getLog, initLogger, isConfigLocked, isSafeMode, setLockConfig, setSafeMode

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

DEFAULT_PARSE_DEPTH

public static final int DEFAULT_PARSE_DEPTH

The maximum number of loops allowed when recursing.

Since:

VelocityTools 1.2

See Also:

• Constant Field Values

KEY_PARSE_DEPTH

@Deprecated
public static final String KEY_PARSE_DEPTH

Deprecated.

See Also:

• Constant Field Values

KEY_CATCH_EXCEPTIONS

@Deprecated
public static final String KEY_CATCH_EXCEPTIONS

Deprecated.

See Also:

• Constant Field Values

KEY_FORCE_THREAD_SAFE

public static final String KEY_FORCE_THREAD_SAFE

See Also:

• Constant Field Values

Constructor Details

RenderTool

public RenderTool()

Method Details

configure

protected void configure(ValueParser parser)

Looks for deprecated parse depth and catch.exceptions properties, as well as any 'forceThreadSafe' setting.

Overrides:

configure in class SafeConfig

Parameters:

parser - configuration values

setVelocityEngine

public void setVelocityEngine(org.apache.velocity.app.VelocityEngine ve)

Allow user to specify a VelocityEngine to be used in place of the Velocity singleton.

Parameters:

ve - VelocityEngine instance

setParseDepth

public void setParseDepth(int depth)

Set the maximum number of loops allowed when recursing.

Parameters:

depth - parse depth

Since:

VelocityTools 1.2

setVelocityContext

public void setVelocityContext(org.apache.velocity.context.Context context)

Sets the Context to be used by the eval(String) and recurse(String) methods.

Parameters:

context - Velocity context

getParseDepth

public int getParseDepth()

Get the maximum number of loops allowed when recursing.

Returns:

parse depth

Since:

VelocityTools 1.2

setCatchExceptions

public void setCatchExceptions(boolean catchExceptions)

Sets whether or not the render() and eval() methods should catch exceptions during their execution or not.

Parameters:

catchExceptions - whether to catch exceptions

Since:

VelocityTools 1.3

getCatchExceptions

public boolean getCatchExceptions()

Returns true if this render() and eval() methods will catch exceptions thrown during rendering.

Returns:

whether to catch exceptions

Since:

VelocityTools 1.3

eval

public String eval(String vtl)
            throws Exception

Evaluates a String containing VTL using the context passed to the setVelocityContext(Context) method. If this tool is request scoped, then this will be the current context and open to modification by the rendered VTL. If application or session scoped, the context will be a new wrapper around the configured context to protect it from modification. The results of the rendering are returned as a String. By default, null will be returned when this throws an exception. This evaluation is not recursive.

Parameters:

vtl - the code to be evaluated

Returns:

the evaluated code as a String

Throws:

Exception - if womething went wrong

recurse

public String recurse(String vtl)
               throws Exception

Recursively evaluates a String containing VTL using the current context, and returns the result as a String. It will continue to re-evaluate the output of the last evaluation until an evaluation returns the same code that was fed into it.

Parameters:

vtl - the code to be evaluated

Returns:

the evaluated code as a String

Throws:

Exception - if womething went wrong

See Also:

• eval(String)

eval

public String eval(org.apache.velocity.context.Context ctx,
 String vtl)
            throws Exception

Evaluates a String containing VTL using the current context, and returns the result as a String. By default if this fails, then null will be returned, though this tool can be configured to let Exceptions pass through. This evaluation is not recursive.

Parameters:

ctx - the current Context

vtl - the code to be evaluated

Returns:

the evaluated code as a String

Throws:

Exception - if womething went wrong

internalEval

protected String internalEval(org.apache.velocity.context.Context ctx,
 String vtl)
                       throws Exception

Throws:

Exception

recurse

public String recurse(org.apache.velocity.context.Context ctx,
 String vtl)
               throws Exception

Recursively evaluates a String containing VTL using the current context, and returns the result as a String. It will continue to re-evaluate the output of the last evaluation until an evaluation returns the same code that was fed into it or the number of recursive loops exceeds the set parse depth.

Parameters:

ctx - the current Context

vtl - the code to be evaluated

Returns:

the evaluated code as a String

Throws:

Exception - if womething went wrong

internalRecurse

protected String internalRecurse(org.apache.velocity.context.Context ctx,
 String vtl,
 int count)
                          throws Exception

Throws:

Exception