Struts String Length Field Validator Example

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:

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:

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

About the Author:

Nam Ha Minh is certified Java programmer (SCJP and SCWCD). He began programming with Java back in the days of Java 1.4 and has been passionate about it ever since. You can connect with him on Facebook and watch his Java videos on YouTube.