## javax.el
Class BeanELResolver

    java.lang.Object
      javax.el.ELResolver
          javax.el.BeanELResolver

    public class BeanELResolver

extends ELResolver

Defines property resolution behavior on objects using the JavaBeans component architecture.

This resolver handles base objects of any type, as long as the base is not `null`. It accepts any object as a property, and coerces it to a string. That string is then used to find a JavaBeans compliant property on the base object. The value is accessed using JavaBeans getters and setters.

This resolver can be constructed in read-only mode, which means that `isReadOnly` will always return `true` and `setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)` will always throw `PropertyNotWritableException`.

`ELResolver`s are combined together using `CompositeELResolver`s, to define rich semantics for evaluating an expression. See the javadocs for `ELResolver` for details.

Because this resolver handles base objects of any type, it should be placed near the end of a composite resolver. Otherwise, it will claim to have resolved a property before any resolvers that come after it get a chance to test if they can do so as well.

Since:
  JSP 2.1
See Also:
  `CompositeELResolver`, `ELResolver`

Nested Class Summary
`protected static class` `BeanELResolver.BeanProperties`
`protected static class` `BeanELResolver.BeanProperty`

Field Summary

Fields inherited from class javax.el.ELResolver
`RESOLVABLE_AT_DESIGN_TIME, TYPE`

Constructor Summary
`BeanELResolver()` Creates a new read/write `BeanELResolver`.
`BeanELResolver(boolean isReadOnly)` Creates a new `BeanELResolver` whose read-only status is determined by the given parameter.

Method Summary
`Class<?>` `getCommonPropertyType(ELContext context, Object base)` If the base object is not `null`, returns the most general type that this resolver accepts for the `property` argument.
`Iterator<FeatureDescriptor>` `getFeatureDescriptors(ELContext context, Object base)` If the base object is not `null`, returns an `Iterator` containing the set of JavaBeans properties available on the given object.
`Class<?>` `getType(ELContext context, Object base, Object property)` If the base object is not `null`, returns the most general acceptable type that can be set on this bean property.
`Object` `getValue(ELContext context, Object base, Object property)` If the base object is not `null`, returns the current value of the given property on this bean.
`boolean` `isReadOnly(ELContext context, Object base, Object property)` If the base object is not `null`, returns whether a call to `setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)` will always fail.
`void` `setValue(ELContext context, Object base, Object property, Object val)` If the base object is not `null`, attempts to set the value of the given property on this bean.

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

Constructor Detail

### BeanELResolver

    public BeanELResolver()

  Creates a new read/write `BeanELResolver`.

### BeanELResolver

    public BeanELResolver(boolean isReadOnly)

  Creates a new `BeanELResolver` whose read-only status is determined by the given parameter.

  Parameters:
    `isReadOnly` - `true` if this resolver cannot modify beans; `false` otherwise.

Method Detail

### getType

    public Class<?> getType(ELContext context,
                            Object base,
                            Object property)

  If the base object is not `null`, returns the most general acceptable type that can be set on this bean property.

  If the base is not `null`, the `propertyResolved` property of the `ELContext` object must be set to `true` by this resolver, before returning. If this property is not `true` after this method is called, the caller should ignore the return value.

  The provided property will first be coerced to a `String`. If there is a `BeanInfoProperty` for this property and there were no errors retrieving it, the `propertyType` of the `propertyDescriptor` is returned. Otherwise, a `PropertyNotFoundException` is thrown.

  Specified by:
    `getType` in class `ELResolver`
  Parameters:
    `context` - The context of this evaluation.
    `base` - The bean to analyze.
    `property` - The name of the property to analyze. Will be coerced to a `String`.
  Returns:
    If the `propertyResolved` property of `ELContext` was set to `true`, then the most general acceptable type; otherwise undefined.
  Throws:
    `NullPointerException` - if context is `null`
    `PropertyNotFoundException` - if `base` is not `null` and the specified property does not exist or is not readable.
    `ELException` - if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.

### getValue

    public Object getValue(ELContext context,
                           Object base,
                           Object property)

  If the base object is not `null`, returns the current value of the given property on this bean.

  If the base is not `null`, the `propertyResolved` property of the `ELContext` object must be set to `true` by this resolver, before returning. If this property is not `true` after this method is called, the caller should ignore the return value.

  The provided property name will first be coerced to a `String`. If the property is a readable property of the base object, as per the JavaBeans specification, then return the result of the getter call. If the getter throws an exception, it is propagated to the caller. If the property is not found or is not readable, a `PropertyNotFoundException` is thrown.

  Specified by:
    `getValue` in class `ELResolver`
  Parameters:
    `context` - The context of this evaluation.
    `base` - The bean on which to get the property.
    `property` - The name of the property to get. Will be coerced to a `String`.
  Returns:
    If the `propertyResolved` property of `ELContext` was set to `true`, then the value of the given property. Otherwise, undefined.
  Throws:
    `NullPointerException` - if context is `null`.
    `PropertyNotFoundException` - if `base` is not `null` and the specified property does not exist or is not readable.
    `ELException` - if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.

### setValue

    public void setValue(ELContext context,
                         Object base,
                         Object property,
                         Object val)

  If the base object is not `null`, attempts to set the value of the given property on this bean.

  If the base is not `null`, the `propertyResolved` property of the `ELContext` object must be set to `true` by this resolver, before returning. If this property is not `true` after this method is called, the caller can safely assume no value was set.

  If this resolver was constructed in read-only mode, this method will always throw `PropertyNotWritableException`.

  The provided property name will first be coerced to a `String`. If property is a writable property of `base` (as per the JavaBeans Specification), the setter method is called (passing `value`). If the property exists but does not have a setter, then a `PropertyNotFoundException` is thrown. If the property does not exist, a `PropertyNotFoundException` is thrown.

  Specified by:
    `setValue` in class `ELResolver`
  Parameters:
    `context` - The context of this evaluation.
    `base` - The bean on which to set the property.
    `property` - The name of the property to set. Will be coerced to a `String`.
    `val` - The value to be associated with the specified key.
  Throws:
    `NullPointerException` - if context is `null`.
    `PropertyNotFoundException` - if `base` is not `null` and the specified property does not exist.
    `PropertyNotWritableException` - if this resolver was constructed in read-only mode, or if there is no setter for the property.
    `ELException` - if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.

### isReadOnly

    public boolean isReadOnly(ELContext context,
                              Object base,
                              Object property)

  If the base object is not `null`, returns whether a call to `setValue(javax.el.ELContext, java.lang.Object, java.lang.Object, java.lang.Object)` will always fail.

  If the base is not `null`, the `propertyResolved` property of the `ELContext` object must be set to `true` by this resolver, before returning. If this property is not `true` after this method is called, the caller can safely assume no value was set.

  If this resolver was constructed in read-only mode, this method will always return `true`.

  The provided property name will first be coerced to a `String`. If property is a writable property of `base`, `false` is returned. If the property is found but is not writable, `true` is returned. If the property is not found, a `PropertyNotFoundException` is thrown.

  Specified by:
    `isReadOnly` in class `ELResolver`
  Parameters:
    `context` - The context of this evaluation.
    `base` - The bean to analyze.
    `property` - The name of the property to analyzed. Will be coerced to a `String`.
  Returns:
    If the `propertyResolved` property of `ELContext` was set to `true`, then `true` if calling the `setValue` method will always fail or `false` if it is possible that such a call may succeed; otherwise undefined.
  Throws:
    `NullPointerException` - if context is `null`
    `PropertyNotFoundException` - if `base` is not `null` and the specified property does not exist.
    `ELException` - if an exception was thrown while performing the property or variable resolution. The thrown exception must be included as the cause property of this exception, if available.

### getFeatureDescriptors

    public Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext context,
                                                             Object base)

  If the base object is not `null`, returns an `Iterator` containing the set of JavaBeans properties available on the given object. Otherwise, returns `null`.

  The `Iterator` returned must contain zero or more instances of `FeatureDescriptor`. Each info object contains information about a property in the bean, as obtained by calling the `BeanInfo.getPropertyDescriptors` method. The `FeatureDescriptor` is initialized using the same fields as are present in the `PropertyDescriptor`, with the additional required named attributes "`type`" and "`resolvableAtDesignTime`" set as follows:

  - `ELResolver.TYPE` - The runtime type of the property, from `PropertyDescriptor.getPropertyType()`.
  - `ELResolver.RESOLVABLE_AT_DESIGN_TIME` - `true`.

  Specified by:
    `getFeatureDescriptors` in class `ELResolver`
  Parameters:
    `context` - The context of this evaluation.
    `base` - The bean to analyze.
  Returns:
    An `Iterator` containing zero or more `FeatureDescriptor` objects, each representing a property on this bean, or `null` if the `base` object is `null`.
  See Also:
    `FeatureDescriptor`

### getCommonPropertyType

    public Class<?> getCommonPropertyType(ELContext context,
                                          Object base)

  If the base object is not `null`, returns the most general type that this resolver accepts for the `property` argument. Otherwise, returns `null`.

  Assuming the base is not `null`, this method will always return `Object.class`. This is because any object is accepted as a key and is coerced into a string.

  Specified by:
    `getCommonPropertyType` in class `ELResolver`
  Parameters:
    `context` - The context of this evaluation.
    `base` - The bean to analyze.
  Returns:
    `null` if base is `null`; otherwise `Object.class`.

Copyright © 2008 Mort Bay Consulting. All Rights Reserved.