The string length field validator checks if length of a String field is within a certain range, e.g. a password must contain at least 6 characters and no more than 12 characters. Using this validator in XML or annotation as follows:

• • XML: using type=”stringlength” attribute in <validator> or <field-validator> elements.
  • Annotation: using @StringLengthFieldValidator annotation type before setter method of the field or action method (in case of plain-validator).

NOTES: This validator does not perform length check if the String field is empty, so it’s recommended to use this validator in conjunction with the required string validator.

 

1. Struts String Length Field Validator XML

Usage:

• Field-validator syntax:
  

  <field name="fieldName">
  	<field-validator type="stringlength">
  		<param name="param name">param value</param>
  		<message>validation error message</message>
  	</field-validator>
  </field>

   

• Plain-validator syntax:
  

  <validator type="stringlength">
  		<param name="param name">param value</param>
  		<message>validation error message</message>
  </validator>

   

Parameters:

Parameter name	Required	Description
fieldName		Name of the field (required if using plain validator syntax).
minLength	No	An integer number specifies minimum length of the field value.
maxLength	No	An integer number specifies maximum length of the field value.
trim	No	Bolean value. If set to true, trim the field value before validating its length. Default is true.
minLengthExpression	No	OGNL expression used to obtain the minimum length value.
maxLengthExpression	No	OGNL expression used to obtain the maximum length value.
trimExpression	No	OGNL expression used to obtain the trim flag.

 

Struts String Length Field Validator XML Examples:

• Field-validator example:

  <field name="password">
  	<field-validator type="stringlength">
  		<param name="minLength">6</param>
  		<param name="maxLength">12</param>
  		<message>Your password must have from ${minLength} to ${maxLength} characters</message>
  	</field-validator>
  </field>

• Only checking the minimum length:

  <field name="password">
  	<field-validator type="stringlength">
  		<param name="minLength">6</param>
  		<message>Your password must have at least ${minLength} characters</message>
  	</field-validator>
  </field>

• Checking for a fixed length:

  <field name="password">
  	<field-validator type="stringlength">
  		<param name="minLength">12</param>
  		<param name="maxLength">12</param>
  		<message>Your password must contain exactly ${maxLength} characters</message>
  	</field-validator>
  </field>

• Using OGNL expressions for minimum and maximum length:

  <field name="password">
  	<field-validator type="stringlength">
  		<param name="minLengthExpression">${minLengthValue}</param>
  		<param name="maxLengthExpression">${maxLengthValue}</param>
  		<message>Your password must have from ${minLength} to ${maxLength} characters</message>
  	</field-validator>
  </field>

  In this case, we have to implement two methods getMinLengthValue() and getMaxLengthValue() in the action or JavaBean class as follows:

  public int getMinLengthValue() {
  	return 6;
  }
  
  public int getMaxLengthValue() {
  	return 12;
  }

   

• Plain-validator example:
  

  <validator type="stringlength">
  	<param name="fieldName">password</param>
  	<param name="minLength">6</param>
  	<param name="maxLength">12</param>
  	   <message>Your password must have from ${minLength} to ${maxLength} characters</message>
  </validator> 

  

2. Struts @StringLengthFieldValidator Annotation

Usage: Annotate the String field’s setter method or action method by the @StringFieldValidatoras follows:

@StringLengthFieldValidator(param1 = "param 1 value", param2 = "param 2 value", ...)

Parameters:

Parameter name	Required	Default value	Description
message	Yes		validation error message.
key	No		i18n key for validation error message.
messageParams	No		Additional parameters to customize the message.
fieldName	No		Specifies field name in case this validator type is plain-validator.
shortCircuit	No	false	Whether this validator is short circuit.
type	No	ValidatorType.FIELD	type of the validator: field-validator (FIELD) or plain-validator (SIMPLE).
minLength	No		The minimum length to check the field value.
minLengthExpression	No		OGNL expression used to obtain the minimum length value.
maxLength	No		The maximum length to check the field value.
maxLengthExpression	No		OGNL expression used to obtain the maximum length value.
trim	No	true	Whether to evaluate trim the field value before validating.
trimExpression	No		OGNL expression used to obtain the trim flag.

 

Struts @StringLengthFieldValidator Annotation Examples:

• Basic field-validator:
  

  @StringLengthFieldValidator(
  		minLength = "6",
  		maxLength = "12",
  		message = "Your password must have from ${minLength} to ${maxLength} characters"
  		)
  public void setPassword(String password) {
  	this.password = password;
  }

   

• Specifying i18n key for the message:
  

  @StringLengthFieldValidator(
  		minLength = "6",
  		maxLength = "12",
  		message = "Default message",
  		key = "form.validation.password"
  		)
  public void setPassword(String password) {
  	this.password = password;
  }

   

• Plain-validator (annotating the action method):
  

  @StringLengthFieldValidator(
  		type = ValidatorType.SIMPLE,
  		fieldName = "password",
  		minLength = "6",
  		maxLength = "12",
  		message = "Your password must have from ${minLength} to ${maxLength} characters"
  		)
  public String execute() {
  	return SUCCESS;
  } 

 

Related Struts Form Validation Tutorials:

• Struts Form Handling Tutorial
• Struts Form Validation Tutorial
• Struts Date Range Field Validator Example
• Struts Integer Range Field Validator Example
• Struts URL Validator Example
• Struts Required Field Validator Example
• Struts Field Expression Validator Example

 

Other Struts Tutorials:

• Introduction to Struts 2 framework
• Struts beginner tutorial (Eclipse + Tomcat + XML)
• Struts Beginner Tutorial with Annotations
• Struts beginner tutorial with Convention Plugin (zero-configuration)
• How to handle exceptions in Struts
• Send e-mail with attachments in Struts
• Struts File Upload Tutorial
• Struts - Spring - Hibernate Integration Tutorial