Mybatis-plus通用查询方法封装

定义DTO

package com.lbdj.user.service.dto;

import com.lbdj.toolkit.utils.ReturnField;
import com.lbdj.toolkit.utils.SFunction;
import lombok.Data;

/**
 * 用户DTO
 *
 * @author 作者
 * @since 2023-06-27
 */
@Data
public class LbdjUserDTO {

    /**
     * 主键
     */
    private Long id;


    private String userNo;

    /**
     * 昵称
     */
    private String nickName;

    /**
     * 密码
     */
    private String password;

    /**
     * 查询条数
     */
    private Integer limit;

    /**
     * 需要返回的列（DTO列名）
     */
    private String columnStr;

    public <T> void setReturnField(SFunction<T, ?>... columns) {
        this.columnStr = ReturnField.select(columns);
    }
}

DTO调用方式

工具类1（适用在没有mybatis-plus包的情况下）

package com.lbdj.toolkit.utils;

import java.io.Serializable;
import java.util.function.Function;

@FunctionalInterface
public interface SFunction<T, R> extends Function<T, R>, Serializable {
}

package com.lbdj.toolkit.utils;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.ObjectStreamClass;
import java.io.Serializable;

@SuppressWarnings("unused")
public class SerializedLambda implements Serializable {

    private static final long serialVersionUID = 8025925345765570181L;

    private Class<?> capturingClass;
    private String functionalInterfaceClass;
    private String functionalInterfaceMethodName;
    private String functionalInterfaceMethodSignature;
    private String implClass;
    private String implMethodName;
    private String implMethodSignature;
    private int implMethodKind;
    private String instantiatedMethodType;
    private Object[] capturedArgs;

    /**
     * 通过反序列化转换 lambda 表达式，该方法只能序列化 lambda 表达式，不能序列化接口实现或者正常非 lambda 写法的对象
     *
     * @param lambda lambda对象
     * @return 返回解析后的 SerializedLambda
     */
    public static SerializedLambda resolve(SFunction<?, ?> lambda) {
        if (!lambda.getClass().isSynthetic()) {
            throw new RuntimeException("该方法仅能传入 lambda 表达式产生的合成类");
        }
        try (ObjectInputStream objIn = new ObjectInputStream(new ByteArrayInputStream(serialize(lambda))) {
            @Override
            protected Class<?> resolveClass(ObjectStreamClass objectStreamClass) throws IOException, ClassNotFoundException {
                Class<?> clazz;
                try {
                    clazz = toClassConfident(objectStreamClass.getName());
                } catch (Exception ex) {
                    clazz = super.resolveClass(objectStreamClass);
                }
                return clazz == java.lang.invoke.SerializedLambda.class ? SerializedLambda.class : clazz;
            }
        }) {
            return (SerializedLambda) objIn.readObject();
        } catch (ClassNotFoundException | IOException e) {
            throw new RuntimeException("This is impossible to happen",e);
        }
    }

    /**
     * 获取接口 class
     *
     * @return 返回 class 名称
     */
    public String getFunctionalInterfaceClassName() {
        return normalizedName(functionalInterfaceClass);
    }


    /**
     * 获取 class 的名称
     *
     * @return 类名
     */
    public String getImplClassName() {
        return normalizedName(implClass);
    }

    /**
     * 获取实现者的方法名称
     *
     * @return 方法名称
     */
    public String getImplMethodName() {
        return implMethodName;
    }

    /**
     * 正常化类名称，将类名称中的 / 替换为 .
     *
     * @param name 名称
     * @return 正常的类名
     */
    private String normalizedName(String name) {
        return name.replace('/', '.');
    }

    /**
     * @return 获取实例化方法的类型
     */
    public Class<?> getInstantiatedType() {
        String instantiatedTypeName = normalizedName(instantiatedMethodType.substring(2, instantiatedMethodType.indexOf(';')));
        return toClassConfident(instantiatedTypeName);
    }

    /**
     * @return 字符串形式
     */
    @Override
    public String toString() {
        String interfaceName = getFunctionalInterfaceClassName();
        String implName = getImplClassName();
        return String.format("%s -> %s::%s",
                interfaceName.substring(interfaceName.lastIndexOf('.') + 1),
                implName.substring(implName.lastIndexOf('.') + 1),
                implMethodName);
    }


    public static Class<?> toClassConfident(String name) {
        try {
            return classForName(name);
        } catch (ClassNotFoundException e) {
            try {
                return Class.forName(name);
            } catch (ClassNotFoundException ex) {
                throw new RuntimeException("找不到指定的class！请仅在明确确定会有 class 的时候，调用该方法", e);
            }
        }
    }

    private static ClassLoaderWrapper classLoaderWrapper = new ClassLoaderWrapper();

    public static Class<?> classForName(String className) throws ClassNotFoundException {
        return classLoaderWrapper.classForName(className);
    }

    public static byte[] serialize(Object object) {
        if (object == null) {
            return null;
        }
        ByteArrayOutputStream baos = new ByteArrayOutputStream(1024);
        try (ObjectOutputStream oos = new ObjectOutputStream(baos)) {
            oos.writeObject(object);
            oos.flush();
        } catch (IOException ex) {
            throw new IllegalArgumentException("Failed to serialize object of type: " + object.getClass(), ex);
        }
        return baos.toByteArray();
    }
}

package com.lbdj.toolkit.utils;

public class ClassLoaderWrapper {

  ClassLoader defaultClassLoader;
  ClassLoader systemClassLoader;

  ClassLoaderWrapper() {
    try {
      systemClassLoader = ClassLoader.getSystemClassLoader();
    } catch (SecurityException ignored) {
      // AccessControlException on Google App Engine
    }
  }

  public Class<?> classForName(String name) throws ClassNotFoundException {
    return classForName(name, getClassLoaders(null));
  }

  Class<?> classForName(String name, ClassLoader[] classLoader) throws ClassNotFoundException {
    for (ClassLoader cl : classLoader) {
      if (null != cl) {
        try {
          return Class.forName(name, true, cl);
        } catch (ClassNotFoundException e) {
          // we'll ignore this until all classloaders fail to locate the class
        }
      }
    }
    throw new ClassNotFoundException("Cannot find class: " + name);
  }

  ClassLoader[] getClassLoaders(ClassLoader classLoader) {
    return new ClassLoader[]{
        classLoader,
        defaultClassLoader,
        Thread.currentThread().getContextClassLoader(),
        getClass().getClassLoader(),
        systemClassLoader};
  }

}

package com.lbdj.toolkit.utils;

import java.lang.ref.WeakReference;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Locale;
import java.util.Map;
import java.util.Optional;
import java.util.concurrent.ConcurrentHashMap;

/**
 * 通过lambda获取字段名
 */
public class ReturnField {

    /**
     * SerializedLambda 反序列化缓存
     */
    private static final Map<String, WeakReference<SerializedLambda>> FUNC_CACHE = new ConcurrentHashMap<>();

    @SafeVarargs
    public final static <T> String select(SFunction<T, ?>... columns) {
        if(columns == null || columns.length == 0){
            return null;
        }
        HashSet<String> returnField = new HashSet<>(8);
        Arrays.stream(columns).forEach(col -> {
            String fieldName = parseFunction(col);
            returnField.add(fieldName);
        });
        StringBuffer colStrBuffer = new StringBuffer();
        returnField.forEach(m -> {
            colStrBuffer.append(m).append(",");
        });
        if (colStrBuffer.toString().endsWith(",")) {
            colStrBuffer.replace(colStrBuffer.toString().length() - 1, colStrBuffer.toString().length(), "");
        }
        String colStr = colStrBuffer.toString();
        return colStr;
    }

    public static <T> String parseFunction(SFunction<T, ?> function) {
        SerializedLambda serializedLambda = resolve(function);
        String fieldName = methodToProperty(serializedLambda.getImplMethodName());
        return fieldName;
    }

    public static String methodToProperty(String name) {
        if (name.startsWith("is")) {
            name = name.substring(2);
        } else {
            if (!name.startsWith("get") && !name.startsWith("set")) {
                throw new RuntimeException("Error parsing property name '" + name + "'.  Didn't start with 'is', 'get' or 'set'.");
            }
            name = name.substring(3);
        }
        if (name.length() == 1 || name.length() > 1 && !Character.isUpperCase(name.charAt(1))) {
            name = name.substring(0, 1).toLowerCase(Locale.ENGLISH) + name.substring(1);
        }
        return name;
    }

    public static <T> SerializedLambda resolve(SFunction<T, ?> func) {
        Class<?> clazz = func.getClass();
        String name = clazz.getName();
        return Optional.ofNullable(FUNC_CACHE.get(name))
                .map(WeakReference::get)
                .orElseGet(() -> {
                    SerializedLambda lambda = SerializedLambda.resolve(func);
                    FUNC_CACHE.put(name, new WeakReference<>(lambda));
                    return lambda;
                });
    }
}

工具类2（适用在有mybatis-plus包的情况下）

Mapper通用查询方法

    @Override
    public List<LbdjUserDTO> selectBase(LbdjUserDTO request) {
        LbdjUser user = BeanConvertUtils.convert(request, LbdjUser::new, null);
        QueryWrapper<LbdjUser> queryWrapper = new QueryWrapper<>();
        //封装返回字段&查询条件
        InitCommonQueryUtils.initQuery(user, request.getColumnStr(), queryWrapper);
        queryWrapper.last(" limit " + request.getLimit());
        List<LbdjUser> result = list(queryWrapper);
        if (CollectionUtils.isEmpty(result)) {
            return Arrays.asList();
        }
        return BeanConvertUtils.convertList(result, LbdjUserDTO::new);
    }

package com.lbdj.user.service.common.utils;

import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.lbdj.user.service.common.advice.exception.RRException;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;

public class InitCommonQueryUtils {
    public static <T> void initQuery(T entity, String columnStr, QueryWrapper<T> queryWrapper) {
        Class<T> type = (Class<T>) entity.getClass();
        TableName annotation = type.getAnnotation(TableName.class);
        if (annotation == null) {
            throw new RRException("非数据库实体类");
        }
        //返回字段
        StringBuilder columns = new StringBuilder();
        //查询条件
        HashMap<String, Object> paramMap = new HashMap<>();

        Field[] declaredFields = type.getDeclaredFields();
        List<String> columnArr = null;
        if (null != columnStr && !"".equals(columnStr)) {
            columnArr = Arrays.asList(columnStr.split(","));
        }
        /**
         * 有兼容历史问题，表中字段半驼峰、非驼峰问题
         */
        for (Field declaredField : declaredFields) {
            //设置属性可访问
            declaredField.setAccessible(true);
            //属性名
            String name = declaredField.getName();
            //获取主键
            TableId tableId = declaredField.getAnnotation(TableId.class);
            //获取非主键的
            TableField tableField = declaredField.getAnnotation(TableField.class);
            //拼接返回字段
            appendReturnField(name, columnArr, columns, tableId, tableField);
            //拼接查询条件
            appendCondition(entity, paramMap, declaredField, name, tableId, tableField);
        }

        //返回字段
        if (columns.length() > 0) {
            queryWrapper.select(columns.toString());
        }
        //查询条件
        if (paramMap.size() > 0) {
            queryWrapper.allEq(paramMap, false);
        }
    }

    private static void appendReturnField(String name,
                                          List<String> columnArr,
                                          StringBuilder columns,
                                          TableId tableId,
                                          TableField tableField) {
        if (null == columnArr) {
            return;
        }
        if (!columnArr.contains(name)) {
            return;
        }
        if (tableId != null) {
            if (columns.length() > 0) {
                columns.append(",");
            }
            columns.append(tableId.value());
            return;
        }
        if (tableField != null) {
            if (columns.length() > 0) {
                columns.append(",");
            }
            if (tableField.exist()) {
                //是数据表字段，不是数据表字段不处理
                columns.append(tableField.value());
            }
        }
    }

    private static <T> void appendCondition(T entity,
                                            HashMap<String, Object> paramMap,
                                            Field declaredField,
                                            String name,
                                            TableId tableId,
                                            TableField tableField) {
        // 获取属性的值
        Object value = null;
        try {
            value = declaredField.get(entity);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        }
        if (null == value) {
            return;
        }
        if (tableId != null) {
            paramMap.put(tableId.value(), value);
            return;
        }
        if (tableField != null) {
            if (tableField.exist()) {
                //是数据表字段，不是数据表字段不处理
                paramMap.put(tableField.value(), value);
            }
            return;
        }
        //处理没有加注解的属性（兼容完全服务驼峰规范的数据表）
        if (!Modifier.isStatic(declaredField.getModifiers())) {
            paramMap.put(name, value);
        }
    }
}