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## org.apache.struts2.components
Class Component

    java.lang.Object
      org.apache.struts2.components.Component

Direct Known Subclasses:
  ContextBean, Else, ElseIf, I18n, If, Include, OptGroup, Param, Property, Push, UIBean

    public class Component

extends Object

Base class to extend for UI components.

This class is a good extension point when building reuseable UI components.

Field Summary
`protected ActionMapper` | `actionMapper`
`static String` | `COMPONENT_STACK`
`protected boolean` | `devMode`
`protected Map` | `parameters`
`protected ValueStack` | `stack`
`protected static ConcurrentMap<Class<?>,Collection<String>>` | `standardAttributesMap` Caches information about common tag's attributes to reduce scanning for annotation @StrutsTagAttribute
`protected boolean` | `throwExceptionOnELFailure`

Constructor Summary
`Component(ValueStack stack)` Constructor.

Method Summary
`void` | `addAllParameters(Map params)` Adds all the given parameters to this component's own parameters.
`void` | `addParameter(String key, Object value)` Adds the given key and value to this component's own parameter.
`boolean` | `altSyntax()` Is the altSyntax enabled? [TRUE] See `struts.properties` where the altSyntax flag is defined.
`protected String` | `completeExpressionIfAltSyntax(String expr)` Adds the sorrounding %{ } to the expression for proper processing.
`void` | `copyParams(Map params)` Pushes this component's parameter Map as well as the component itself on to the stack and then copies the supplied parameters over.
`protected String` | `determineActionURL(String action, String namespace, String method, javax.servlet.http.HttpServletRequest req, javax.servlet.http.HttpServletResponse res, Map parameters, String scheme, boolean includeContext, boolean encodeResult, boolean forceAddSchemeHostAndPort, boolean escapeAmp)` Renders an action URL by consulting the `ActionMapper`.
`protected String` | `determineNamespace(String namespace, ValueStack stack, javax.servlet.http.HttpServletRequest req)` Determines the namespace of the current page being renderdd.
`boolean` | `end(Writer writer, String body)` Callback for the end tag of this component.
`protected boolean` | `end(Writer writer, String body, boolean popComponentStack)` Callback for the start tag of this component.
`protected StrutsException` | `fieldError(String field, String errorMsg, Exception e)` Constructs a `RuntimeException` based on the given information.
`protected Component` | `findAncestor(Class clazz)` Finds the nearest ancestor of this component stack.
`protected String` | `findString(String expr)` Evaluates the OGNL stack to find a String value.
`protected String` | `findString(String expr, String field, String errorMsg)` Evaluates the OGNL stack to find a String value.
`protected String` | `findStringIfAltSyntax(String expr)` This check is needed for backwards compatibility with 2.1.x
`protected Object` | `findValue(String expr)` Finds a value from the OGNL stack based on the given expression.
`protected Object` | `findValue(String expr, Class toType)` Evaluates the OGNL stack to find an Object of the given type.
`protected Object` | `findValue(String expr, String field, String errorMsg)` Evaluates the OGNL stack to find an Object value.
`Stack<Component>` | `getComponentStack()` Gets the component stack of this component.
`Map` | `getParameters()` Gets the parameters.
`ValueStack` | `getStack()` Gets the OGNL value stack assoicated with this component.
`protected Collection<String>` | `getStandardAttributes()` If needed caches all methods annotated by given annotation to avoid further scans
`boolean` | `isValidTagAttribute(String attrName)` Checks if provided name is a valid tag's attribute
`protected void` | `popComponentStack()` Pops the component stack.
`void` | `setActionMapper(ActionMapper mapper)`
`void` | `setDevMode(String devMode)`
`void` | `setThrowExceptionsOnELFailure(String throwException)`
`void` | `setUrlHelper(UrlHelper urlHelper)`
`boolean` | `start(Writer writer)` Callback for the start tag of this component.
`protected String` | `stripExpressionIfAltSyntax(String expr)` If altsyntax (%{...}) is applied, simply strip the "%{" and "}" off.
`protected String` | `toString(Throwable t)` Constructs a string representation of the given exception.
`boolean` | `usesBody()` Overwrite to set if body should be used.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### COMPONENT_STACK

    public static final String COMPONENT_STACK

See Also:
  Constant Field Values

### standardAttributesMap

    protected static ConcurrentMap<Class<?>,Collection<String>> standardAttributesMap

  Caches information about common tag's attributes to reduce scanning for annotation @StrutsTagAttribute

### devMode

    protected boolean devMode

### stack

    protected ValueStack stack

### parameters

    protected Map parameters

### actionMapper

    protected ActionMapper actionMapper

### throwExceptionOnELFailure

    protected boolean throwExceptionOnELFailure

Constructor Detail

### Component

    public Component(ValueStack stack)

  Constructor.

  Parameters:
    `stack` - OGNL value stack.

Method Detail

### setDevMode

    public void setDevMode(String devMode)

### setActionMapper

    public void setActionMapper(ActionMapper mapper)

### setThrowExceptionsOnELFailure

    public void setThrowExceptionsOnELFailure(String throwException)

### setUrlHelper

    public void setUrlHelper(UrlHelper urlHelper)

### getStack

    public ValueStack getStack()

  Gets the OGNL value stack assoicated with this component.

  Returns:
    the OGNL value stack assoicated with this component.

### getComponentStack

    public Stack<Component> getComponentStack()

  Gets the component stack of this component.

  Returns:
    the component stack of this component, never `null`.

### start

    public boolean start(Writer writer)

  Callback for the start tag of this component. Should the body be evaluated?

  Parameters:
    `writer` - the output writer.
  Returns:
    true if the body should be evaluated

### end

    public boolean end(Writer writer,
                       String body)

  Callback for the end tag of this component. Should the body be evaluated again?

  NOTE: will pop component stack.

  Parameters:
    `writer` - the output writer.
    `body` - the rendered body.
  Returns:
    true if the body should be evaluated again

### end

    protected boolean end(Writer writer,
                          String body,
                          boolean popComponentStack)

  Callback for the start tag of this component. Should the body be evaluated again?

  NOTE: has a parameter to determine to pop the component stack.

  Parameters:
    `writer` - the output writer.
    `body` - the rendered body.
    `popComponentStack` - should the component stack be popped?
  Returns:
    true if the body should be evaluated again

### popComponentStack

    protected void popComponentStack()

  Pops the component stack.

### findAncestor

    protected Component findAncestor(Class clazz)

  Finds the nearest ancestor of this component stack.

  Parameters:
    `clazz` - the class to look for, or if assignable from.
  Returns:
    the component if found, `null` if not.

### findString

    protected String findString(String expr)

  Evaluates the OGNL stack to find a String value.

  Parameters:
    `expr` - OGNL expression.
  Returns:
    the String value found.

### findString

    protected String findString(String expr,
                                String field,
                                String errorMsg)

  Evaluates the OGNL stack to find a String value.

  If the given expression is `null` a error is logged and a `RuntimeException` is thrown constructed with a messaged based on the given field and errorMsg paramter.

  Parameters:
    `expr` - OGNL expression.
    `field` - field name used when throwing `RuntimeException`.
    `errorMsg` - error message used when throwing `RuntimeException`.
  Returns:
    the String value found.
  Throws:
    `StrutsException` - is thrown in case of expression is `null`.

### fieldError

    protected StrutsException fieldError(String field,
                                         String errorMsg,
                                         Exception e)

  Constructs a `RuntimeException` based on the given information.

  A message is constructed and logged at ERROR level before being returned as a `RuntimeException`.

  Parameters:
    `field` - field name used when throwing `RuntimeException`.
    `errorMsg` - error message used when throwing `RuntimeException`.
    `e` - the caused exception, can be `null`.
  Returns:
    the constructed `StrutsException`.

### findValue

    protected Object findValue(String expr)

  Finds a value from the OGNL stack based on the given expression. Will always evaluate `expr` against stack except when `expr` is null. If altsyntax (%{...}) is applied, simply strip it off.

  Parameters:
    `expr` - the expression. Returns `null` if expr is null.
  Returns:
    the value, `null` if not found.

### stripExpressionIfAltSyntax

    protected String stripExpressionIfAltSyntax(String expr)

  If altsyntax (%{...}) is applied, simply strip the "%{" and "}" off.

  Parameters:
    `expr` - the expression (must be not null)
  Returns:
    the stripped expression if altSyntax is enabled. Otherwise the parameter expression is returned as is.

### altSyntax

    public boolean altSyntax()

  Is the altSyntax enabled? [TRUE]

  See `struts.properties` where the altSyntax flag is defined.

### completeExpressionIfAltSyntax

    protected String completeExpressionIfAltSyntax(String expr)

  Adds the sorrounding %{ } to the expression for proper processing.

  Parameters:
    `expr` - the expression.
  Returns:
    the modified expression if altSyntax is enabled, or the parameter expression otherwise.

### findStringIfAltSyntax

    protected String findStringIfAltSyntax(String expr)

  This check is needed for backwards compatibility with 2.1.x

  Parameters:
    `expr` - the expression.
  Returns:
    the found string if altSyntax is enabled. The parameter expression otherwise.

### findValue

    protected Object findValue(String expr,
                               String field,
                               String errorMsg)

  Evaluates the OGNL stack to find an Object value.

  Function just like `findValue(String)` except that if the given expression is `null` a error is logged and a `RuntimeException` is thrown constructed with a messaged based on the given field and errorMsg paramter.

  Parameters:
    `expr` - OGNL expression.
    `field` - field name used when throwing `RuntimeException`.
    `errorMsg` - error message used when throwing `RuntimeException`.
  Returns:
    the Object found, is never `null`.
  Throws:
    `StrutsException` - is thrown in case of not found in the OGNL stack, or expression is `null`.

### findValue

    protected Object findValue(String expr,
                               Class toType)

  Evaluates the OGNL stack to find an Object of the given type. Will evaluate `expr` the portion wrapped with altSyntax (%{...}) against stack when altSyntax is on, else the whole `expr` is evaluated against the stack.

  This method only supports the altSyntax. So this should be set to true.

  Parameters:
    `expr` - OGNL expression.
    `toType` - the type expected to find.
  Returns:
    the Object found, or `null` if not found.

### determineActionURL

    protected String determineActionURL(String action,
                                        String namespace,
                                        String method,
                                        javax.servlet.http.HttpServletRequest req,
                                        javax.servlet.http.HttpServletResponse res,
                                        Map parameters,
                                        String scheme,
                                        boolean includeContext,
                                        boolean encodeResult,
                                        boolean forceAddSchemeHostAndPort,
                                        boolean escapeAmp)

  Renders an action URL by consulting the `ActionMapper`.

  Parameters:
    `action` - the action
    `namespace` - the namespace
    `method` - the method
    `req` - HTTP request
    `res` - HTTP response
    `parameters` - parameters
    `scheme` - http or https
    `includeContext` - should the context path be included or not
    `encodeResult` - should the url be encoded
    `forceAddSchemeHostAndPort` - should the scheme host and port be forced
    `escapeAmp` - should ampersand (&) be escaped to &
  Returns:
    the action url.

### determineNamespace

    protected String determineNamespace(String namespace,
                                        ValueStack stack,
                                        javax.servlet.http.HttpServletRequest req)

  Determines the namespace of the current page being renderdd. Useful for Form, URL, and href generations.

  Parameters:
    `namespace` - the namespace
    `stack` - OGNL value stack
    `req` - HTTP request
  Returns:
    the namepsace of the current page being rendered, is never `null`.

### copyParams

    public void copyParams(Map params)

  Pushes this component's parameter Map as well as the component itself on to the stack and then copies the supplied parameters over. Because the component's parameter Map is pushed before the component itself, any key-value pair that can't be assigned to component will be set in the parameters Map.

  Parameters:
    `params` - the parameters to copy.

### toString

    protected String toString(Throwable t)

  Constructs a string representation of the given exception.

  Parameters:
    `t` - the exception
  Returns:
    the exception as a string.

### getParameters

    public Map getParameters()

  Gets the parameters.

  Returns:
    the parameters. Is never `null`.

### addAllParameters

    public void addAllParameters(Map params)

  Adds all the given parameters to this component's own parameters.

  Parameters:
    `params` - the parameters to add.

### addParameter

    public void addParameter(String key,
                             Object value)

  Adds the given key and value to this component's own parameter.

  If the provided key is `null` nothing happens. If the provided value is `null` any existing parameter with the given key name is removed.

  Parameters:
    `key` - the key of the new parameter to add.
    `value` - the value assoicated with the key.

### usesBody

    public boolean usesBody()

  Overwrite to set if body should be used.

  Returns:
    always false for this component.

### isValidTagAttribute

    public boolean isValidTagAttribute(String attrName)

  Checks if provided name is a valid tag's attribute

  Parameters:
    `attrName` - String name of attribute
  Returns:
    true if attribute with the same name was already defined

### getStandardAttributes

    protected Collection<String> getStandardAttributes()

  If needed caches all methods annotated by given annotation to avoid further scans

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