我喜欢Jakub Jirutka使用Spring表达式语言的想法。如果您不想添加另一个库/依赖项(假设您已经使用了Spring)，下面是他的想法的简化实现。

约束:

@Constraint(validatedBy=ExpressionAssertValidator.class)
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface ExpressionAssert {
    String message() default "expression must evaluate to true";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
    String value();
}

验证器:

public class ExpressionAssertValidator implements ConstraintValidator<ExpressionAssert, Object> {
    private Expression exp;

    public void initialize(ExpressionAssert annotation) {
        ExpressionParser parser = new SpelExpressionParser();
        exp = parser.parseExpression(annotation.value());
    }

    public boolean isValid(Object value, ConstraintValidatorContext context) {
        return exp.getValue(value, Boolean.class);
    }
}

像这样应用:

@ExpressionAssert(value="pass == passVerify", message="passwords must be same")
public class MyBean {
    @Size(min=6, max=50)
    private String pass;
    private String passVerify;
}

我很惊讶这个没有开箱即用。不管怎样，这里有一个可能的解决方案。

我创建了一个类级验证器，而不是原始问题中描述的字段级验证器。

下面是注释代码:

package com.moa.podium.util.constraints;

import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.*;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import javax.validation.Constraint;
import javax.validation.Payload;

@Target({TYPE, ANNOTATION_TYPE})
@Retention(RUNTIME)
@Constraint(validatedBy = MatchesValidator.class)
@Documented
public @interface Matches {

  String message() default "{com.moa.podium.util.constraints.matches}";

  Class<?>[] groups() default {};

  Class<? extends Payload>[] payload() default {};

  String field();

  String verifyField();
}

以及验证器本身:

package com.moa.podium.util.constraints;

import org.mvel2.MVEL;

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;

public class MatchesValidator implements ConstraintValidator<Matches, Object> {

  private String field;
  private String verifyField;


  public void initialize(Matches constraintAnnotation) {
    this.field = constraintAnnotation.field();
    this.verifyField = constraintAnnotation.verifyField();
  }

  public boolean isValid(Object value, ConstraintValidatorContext context) {
    Object fieldObj = MVEL.getProperty(field, value);
    Object verifyFieldObj = MVEL.getProperty(verifyField, value);

    boolean neitherSet = (fieldObj == null) && (verifyFieldObj == null);

    if (neitherSet) {
      return true;
    }

    boolean matches = (fieldObj != null) && fieldObj.equals(verifyFieldObj);

    if (!matches) {
      context.disableDefaultConstraintViolation();
      context.buildConstraintViolationWithTemplate("message")
          .addNode(verifyField)
          .addConstraintViolation();
    }

    return matches;
  }
}

注意，我已经使用MVEL来检查正在验证的对象的属性。这可以用标准反射api代替，或者如果它是您正在验证的特定类，则使用访问器方法本身。

@Matches注释可以像下面这样使用在bean上:

@Matches(field="pass", verifyField="passRepeat")
public class AccountCreateForm {

  @Size(min=6, max=50)
  private String pass;
  private String passRepeat;

  ...
}

作为免责声明，我在最后5分钟写了这篇文章，所以我可能还没有解决所有的错误。如果有任何错误，我将更新答案。

我尝试了Alberthoven的例子(hibernate-validator 4.0.2.GA)，我得到了一个ValidationException:“带注释的方法必须遵循JavaBeans命名约定。Match()没有。”。在我将方法从“match”重命名为“isValid”后，它就工作了。

public class Password {

    private String password;

    private String retypedPassword;

    public Password(String password, String retypedPassword) {
        super();
        this.password = password;
        this.retypedPassword = retypedPassword;
    }

    @AssertTrue(message="password should match retyped password")
    private boolean isValid(){
        if (password == null) {
            return retypedPassword == null;
        } else {
            return password.equals(retypedPassword);
        }
    }

    public String getPassword() {
        return password;
    }

    public String getRetypedPassword() {
        return retypedPassword;
    }

}

如果您正在使用Spring框架，那么您可以使用Spring表达式语言(SpEL)。我写了一个小库，提供了基于SpEL的JSR-303验证器——它使得跨领域验证变得轻而易举!看看https://github.com/jirutka/validator-spring。

这将验证密码字段的长度和相等性。

@SpELAssert(value = "pass.equals(passVerify)",
            message = "{validator.passwords_not_same}")
public class MyBean {

    @Size(min = 6, max = 50)
    private String pass;

    private String passVerify;
}

您还可以轻松地进行修改，仅当密码字段不为空时才验证密码字段。

@SpELAssert(value = "pass.equals(passVerify)",
            applyIf = "pass || passVerify",
            message = "{validator.passwords_not_same}")
public class MyBean {

    @Size(min = 6, max = 50)
    private String pass;

    private String passVerify;
}

为什么不试试Oval: http://oval.sourceforge.net/呢

我看起来像它支持OGNL，所以也许你可以用更自然的方式来做

@Assert(expr = "_value ==_this.pass").

我建议你另一种可能的解决办法。也许不那么优雅，但更容易!

public class MyBean {
  @Size(min=6, max=50)
  private String pass;

  private String passVerify;

  @NotNull
  private LocalDate passExpiry;
  @NotNull
  private LocalDate dateOfJoining;

  @AssertTrue(message = "Fields `pass` and `passVerify` should be equal")
  // Any method name is ok als long it begins with `is`
  private boolean isValidPass() {
    //return pass == null && passVerify == null || pass.equals(passVerify);
    // Since Java 7:
    return Objects.equals(pass, passVerify);
  }

  @AssertTrue(message = "Field `passExpiry` should be later than `dateOfJoining`")
  // Other rules can also be validated in other methods
  private boolean isPassExpiryAfterDateOfJoining() {
    return dateOfJoining.isBefore(passExpiry);
  }
}

isValid()和isPassExpiryAfterDateOfJoining()方法由验证器自动调用。在ConstraintViolations中报告的属性路径将从方法名中提取:valid和passExpiryAfterDateOfJoining。