mybatis-plus链式调用的实现示例

public class LambdaQueryWrapper<T> extends AbstractLambdaWrapper<T, LambdaQueryWrapper<T>>
    implements Query<LambdaQueryWrapper<T>, T, SFunction<T, ?>> {
	// 省略构造函数

    /**
     * SELECT 部分 SQL 设置
     *
     * @param columns 查询字段
     */
    @SafeVarargs
    @Override
    public final LambdaQueryWrapper<T> select(SFunction<T, ?>... columns) {
        if (ArrayUtils.isNotEmpty(columns)) {
            this.sqlSelect.setStringValue(columnsToString(false, columns));
        }
        return typedThis;
    }    @Override
    public LambdaQueryWrapper<T> select(Class<T> entityClass, Predicate<TableFieldInfo> predicate) {
        if (entityClass == null) {
            entityClass = getEntityClass();
        } else {
            setEntityClass(entityClass);
        }
        Assert.notNull(entityClass, "entityClass can not be null");
        this.sqlSelect.setStringValue(TableInfoHelper.getTableInfo(entityClass).chooseSelect(predicate));
        return typedThis;
    }

public abstract class AbstractWrapper<T, R, Children extends AbstractWrapper<T, R, Children>> extends Wrapper<T>
    implements Compare<Children, R>, Nested<Children, Children>, Join<Children>, Func<Children, R> {

    /**
     * 占位符
     */
    protected final Children typedThis = (Children) this;
 	// 省略其余全局变量

    @Override
    public T getEntity() {
        return entity;
    }

    public Children setEntity(T entity) {
        this.entity = entity;
        return typedThis;
    }
	//普通query的R指定的String，lambda的R指定的SFunction，用来实现方法的引用
    @Override
    public Children eq(boolean condition, R column, Object val) {
        return addCondition(condition, column, EQ, val);
    }

public class QueryWrapper<T> extends AbstractWrapper<T, String, QueryWrapper<T>>
    implements Query<QueryWrapper<T>, T, String> {

public abstract class AbstractLambdaWrapper<T, Children extends AbstractLambdaWrapper<T, Children>>
        extends AbstractWrapper<T, SFunction<T, ?>, Children> {

@Slf4j
public abstract class AbstractLambdaESignBuilder <Children extends AbstractLambdaESignBuilder<Children>>{

    /**
     * 占位符
     */
    protected final Children typedThis = (Children) this;

    public Children preview(ESignInitiateParam initiateParam){
        CreateDocTemplate createDocTemplate = new CreateDocTemplate();
        createDocTemplate.setDocTemplateId(eSignConfig.getDocTemplateId());
        createDocTemplate.setFileName(eSignConfig.getFileName());
        List<Component> components = buildDebt(initiateParam);
        createDocTemplate.setComponents(components);
        body = JSONObject.toJSONString(createDocTemplate);
        return typedThis;
    }

    public Children sortAPIUrl(String apiUrl){
        this.sortApiUrl = apiUrl;
        return typedThis;
    }

    protected abstract ESignModel get(String msg, String responseMsg);

    protected abstract Children config(ESignConfig eSignConfig);
}

@Slf4j
@Service
public class LambdaESignBuilder extends AbstractLambdaESignBuilder<LambdaESignBuilder> {
    @Override
    public LambdaESignBuilder config(ESignConfig eSignConfig) {
        super.eSignConfig = eSignConfig;
        return super.typedThis;
    }
}