将自定义对象从thymeleaf视图传递到控制器

Question

Trying to pass Custom made objects using to th:value from View to Controller but only able to pass Java's primitive Data types through th:value . Is there any way I can send complex objects through th:value

I am new to spring and trying out some random things. It is a simple web application.

What I'm trying to do:

I have a form for creating a team. The form includes a text field for a team name and a bunch of checkboxes to select the team members. For each selected checkbox the corresponding member should be added into the team list.

I tried using thymeleaf's th:value attribute to pass objects from View to Controller. But I can only pass String values using th:value

teamCreationForm.html

package com.example.kkvamshee.Cricket;

import lombok.Data;

import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;
import java.util.List;

@Data
public class Team {
    @NotNull private String name;

    @Size(min = 3, max = 3, message = "You can only have 3 members on the team")
    private List<Player> players;
}

CreateTeamController.java

 package com.example.kkvamshee.Cricket.web; import com.example.kkvamshee.Cricket.Player; import com.example.kkvamshee.Cricket.Team; import com.example.kkvamshee.Cricket.data.JdbcPlayerRepository; import lombok.extern.slf4j.Slf4j; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Controller; import org.springframework.ui.Model; import org.springframework.validation.Errors; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.PostMapping; import org.springframework.web.bind.annotation.RequestMapping; import javax.validation.Valid; import java.util.List; @Slf4j @Controller @RequestMapping("/create-your-team") public class CreateTeamController { .... @GetMapping public String showSelectTeamPage(Model model) { List<Player> playersList = playerRepo.findAll(); model.addAttribute("playersList", playersList); model.addAttribute("team", new Team()); return "teamCreationForm"; } ..... } 

Team.java

 package com.example.kkvamshee.Cricket; import lombok.Data; import javax.validation.constraints.NotNull; import javax.validation.constraints.Size; import java.util.List; @Data public class Team { @NotNull private String name; @Size(min = 3, max = 3, message = "You can only have 3 members on the team") private List<Player> players; } 

Error Log

 Field error in object 'team' on field 'players': rejected value [Player(name=vamshee, age=20, exp=1),Player(name=messi, age=32, exp=18),Player(name=ronaldo, age=34, exp=18)]; codes [typeMismatch.team.players,typeMismatch.players,typeMismatch.java.util.List,typeMismatch]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [team.players,players]; arguments []; default message [players]]; default message [Failed to convert property value of type 'java.lang.String[]' to required type 'java.util.List' for property 'players'; nested exception is java.lang.IllegalStateException: Cannot convert value of type 'java.lang.String' to required type 'com.example.kkvamshee.Cricket.Player' for property 'players[0]': no matching editors or conversion strategy found] 

At the end of thid error log, there is "no matching editors or conversion strategy found".

I tried changing the th:valueType to Integer and it successfully casted corresponding text into Integer values. But i get this casting error doing the same thing with Team object or any other custom made object for instance.

Answer 1

Thymeleaf can know which object you are working with especially if you have it mapped correctly and accepting it appropriately. Look at the test I did with your code.

Please watch how the action is introduced in the form.

Answer 2

Template engine has to convert the <input ... th:value="${player}"> tag into HTML(something a browser can understand) and the converted tag looks like <input ... value="string returned by player.toString()"> .

So, the view has no idea of the Object Player . The value is just a simple string to the view. Spring needs some converter to convert the string to an appropriate Player Object.

This can be done by implementing Converter<String, Player> Interface and then registering the Converter in our application.

Implementation of Converter Interface :

package com.example.kkvamshee.cricket.config;

import com.example.kkvamshee.cricket.Player;
import lombok.extern.slf4j.Slf4j;
import org.springframework.core.convert.converter.Converter;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

@Slf4j
public class StringToPlayerConverter implements Converter<String, Player> {

    @Override
    public Player convert(String source) {
        String pattern = "Player\\(name=([a-zA-z0-9]+), age=([1-9]+), exp=([1-9]+)\\)";

        Matcher matcherResult = Pattern.compile(pattern).matcher(source);

        log.info("regex result : " + matcherResult.find());

        String name = matcherResult.group(1);
        int age = Integer.parseInt(matcherResult.group(2));
        int exp = Integer.parseInt(matcherResult.group(3));

        return new Player(name, age, exp);
    }
}

Registering the above Converter Object :

package com.example.kkvamshee.cricket.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.format.FormatterRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
public class WebConfig implements WebMvcConfigurer {

    @Override
    public void addFormatters(FormatterRegistry registry) {
        registry.addConverter(new StringToPlayerConverter());
    }
}

There are various methods to acheive this type conversion.

For more details refer to the documentation