Java日常编码小知识点

Posted 2022-02-01 master-dragon

LinkedHashMap

日常工作通常都是HashMap，有时候与前端对接返回，按顺序显示map结果，这时需要考虑有序；而java.util中提供了LinkedHashMap, 可参考学习:linked_hash_map

反射的小应用

属性类，json存到数据库中，可能有增减; 与前端对接时，希望一个json传递过来设置，而后端也最好不用麻烦的写个中间DO转换设置

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.JSONArray;

import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

/**
 * @Author mubi
 * @Date 2021/10/3 10:26
 */
public class ProjectProperty 
    private String name;
    private Integer projectId;
    private List<String> projectItems;
    private List<Integer> ids;

    public static ProjectProperty constructFromJson(String jsonStr)
        Map<String, Object> map = JSON.parseObject(jsonStr, Map.class);

        ProjectProperty projectProperty = new ProjectProperty();
        Class clz = projectProperty.getClass();
        Field[] fields = clz.getDeclaredFields();
        Map<String, Field> fieldNameMap = new HashMap(fields.length);
        for (Field field : fields) 
            fieldNameMap.put(field.getName(), field);
        
        for (Map.Entry<String, Object> entry : map.entrySet()) 
            String property = entry.getKey();
            Object value = entry.getValue();
            if (fieldNameMap.containsKey(property)) 
                try 
                    Field field = fieldNameMap.get(property);
                    field.setAccessible(true);
                    // String
                    if (field.getType() == String.class) 
                        field.set(projectProperty, String.valueOf(value));
                    
                    // Integer
                    else if (field.getType() == Integer.class) 
                        field.set(projectProperty, Integer.parseInt(String.valueOf(value)));
                    
                    // List
                    else if (field.getType() == List.class) 
                        JSONArray array = (JSONArray) value;
                        List<Object> list = new ArrayList<>();
                        array.forEach(o -> list.add(o));
                        field.set(projectProperty, list);
                    
                    else 
                        field.set(projectProperty, value);
                    
                 catch (Exception e) 
                    e.printStackTrace();
                
            
        
        LinkedHashMap
        return projectProperty;
    

    public String getName() 
        return name;
    

    public void setName(String name) 
        this.name = name;
    

    public Integer getProjectId() 
        return projectId;
    

    public void setProjectId(Integer projectId) 
        this.projectId = projectId;
    

    public List<String> getProjectItems() 
        return projectItems;
    

    public void setProjectItems(List<String> projectItems) 
        this.projectItems = projectItems;
    

    public List<Integer> getIds() 
        return ids;
    

    public void setIds(List<Integer> ids) 
        this.ids = ids;
    

测试

import com.alibaba.fastjson.JSON;
import com.example.demoapi.domain.ProjectProperty;
import org.junit.Assert;
import org.junit.Test;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @Author mubi
 * @Date 2021/6/5 10:59
 */
public class ProjectPropertyTest 

    @Test
    public void test() throws Exception 
        Map<String, Object> map = new HashMap();
        map.put("name", "abc");
        map.put("projectId", 123);
        List<String> projectItems = new ArrayList()
            add("pro1");
            add("pro2");
        ;
        map.put("projectItems", projectItems);
        List<Integer> ids = new ArrayList()
            add(1);
            add(2);
        ;
        map.put("ids", ids);

        String jsonStr = JSON.toJSONString(map);
        ProjectProperty projectProperty = ProjectProperty.constructFromJson(jsonStr);
        Assert.assertNotNull(projectProperty);
    

TODO