类函数式的sql生成工具类的封装

2019-07-04 00:00:00 函数 生成 封装

前言

自从正式工作以来,公司一直用的是Spring 原生的JDBC Template以及在其上封装的扩展的一些小工具, 而摈弃了Mybatis、ibatis等ORM框架。总的来说,这种做法对于开发效率来说提高不少,由于真正的查库操作不会直接穿透到Mysql,所以抗压性也没有太大的问题。

问题

虽说直接使用原生的JDBC Template比较方便,但是构造参数条件,以及生成查询语句过于简单粗暴,导致代码不简洁,复用度也不高。举个例子,根据特定的条件查询用户:

StringBuffer sqlBuilder = new StringBuffer("select * from user where ");
    Map<String, Object> paramsMap = new HashMap<>();
    if (userId != null) {
      sqlBuilder.append("user_id=:userId");
      paramsMap.put("userId", userId);
    }
    if (batchNumber != null) {
      sqlBuilder.append("batch_number=:batchNumber");
      paramsMap.put("batchNumber", batchNumber);
    }
    if (status != null) {
      sqlBuilder.append("status=:status");
      paramsMap.put("stats", status);
    }


    if (page > 0 && count > 0) {
      sqlBuilder.append(" limit ")
          .append(page * count)
          .append(", ")
          .append(count);
    }
    //生成sql语句
    sqlBuilder.toString();

可以看到上面的代码大部分在重复同样的逻辑,20多行的代码仅仅只是在构造sql语句以及收集参数,而且这些重复的代码将充斥项目所有的DAO层,导致代码非常不整洁。维护困难。

sql生成工具类封装

秉承着恶心重复的代码要重构抽象的态度,对sql生成的步骤,做了一次简单的封装:

  • 先介绍接口
public interface Order {
    Where desc();


    Where asc();
  }


public interface Where {
    Where ifPresent(Object value, String sql);


    Order orderBy(String field);


    Where limit(int begin, int end);


    Where in(List<Object> values, String sql);


    String sql();//构造的sql


    Map<String, Object> params();//参数值
  }

根据sql语句的特点,抽出子句部分的生成单独构造,涵盖Where, in(暂未实现),limit 以及 order 排序规则。

  • 来看看接口的实现

将所有相关的类通过内部静态类封装入SqlWhereBuffer类中。

public class SqlWhereBuffer {


  public static SqlWhereBuffer.Where builder() {
    return new Builder();
  }


  static class Builder implements SqlWhereBuffer.Order, SqlWhereBuffer.Where {
    private List<String> sql = new ArrayList<>();
    private Map<String, Object> params = new HashMap<>();
    private String orderBy = " ";
    private String limit = " ";
    private String in = " ";
    private List<SqlMapperPlugin> sqlMapperPlugins;


    public Builder() {
      //添加基本类型默认的插件       sqlMapperPlugins = Lists.newArrayList();
      this.mapperPlugins(SqlMapperPlugin.EnumSqlPlugin)
          .mapperPlugins(SqlMapperPlugin.BooleanSqlPlugin);
    }


    public Builder mapperPlugins(SqlMapperPlugin sqlMapperPlugin) {
      if (CollectionUtils.isEmpty(sqlMapperPlugins)) {
        sqlMapperPlugins = Lists.newArrayList();
      }
      sqlMapperPlugins.add(sqlMapperPlugin);
      return this;
    }


    @Override
    public SqlWhereBuffer.Where ifPresent(Object value, String sql) {
      Optional.ofNullable(value)
          .ifPresent(val -> {
            this.sql.add(sql);
            Pattern pattern = Pattern.compile(":([a-z,A-Z,\\w,_]*)"); //固定的sql参数模式             Matcher matcher = pattern.matcher(sql);
            if (!matcher.find()) {
              throw new IllegalArgumentException(sql + " don't include :name");
            }


            Optional<SqlMapperPlugin> mapper = sqlMapperPlugins.stream()
                .filter(sqlMapperPlugin -> sqlMapperPlugin.test(val))
                .findFirst();
            if (mapper.isPresent()) {
              params.putAll(mapper.get()
                  .getParams(matcher.group(1), value));
            } else {
              //匹配不到走默认的插件               params.put(matcher.group(1), value);
            }
          });
      return this;
    }


    @Override
    public SqlWhereBuffer.Order orderBy(String field) {
      orderBy += "ORDER BY " + field;
      return this;
    }


    @Override
    public SqlWhereBuffer.Where limit(int offset, int count) {
      limit += "limit " + offset + "," + count;
      return this;
    }
    @Override
    public String sql() {
      if (sql.isEmpty() || params.isEmpty()) {
        return "";
      } else {
        return " WHERE " + sql.stream()
            .collect(Collectors.joining(" AND ")) + orderBy + limit;
      }
    }


    @Override
    public ImmutableMap<String, Object> params() {
      return ImmutableMap.copyOf(params);
    }


    @Override
    public SqlWhereBuffer.Where desc() {
      orderBy += " DESC";
      return this;
    }


    @Override
    public SqlWhereBuffer.Where asc() {
      return this;
    }
  }
}

静态类Builder实现了SqlWhereBuffer.Order, SqlWhereBuffer.Where这俩个接口的方法。ifPresent是主入口。流程如下:

1、在ifPresent中参数先进行非空判断,如果是空则直接过滤掉;
2、然后通过一个正则表达式(**:([a-z,A-Z,\\w,_]*)**)对参数sql进行规则校验,如果不符合也将过滤;
3、最后value通过一系列的自定义的注册插件的匹配判断,得出sql以及params。


  • 关于自定义插件,本没想做这么复杂,然而在实际的使用过程中,JDBC Template对Enum的支持不够…不过想也是,Enum大多是自定义的,没法做到一套约定的接口满足所有需求。于是封装了一个插件类,方便以后扩展:
public static class SqlMapperPlugin {
    private final Predicate<Object> predicate;
    private final ParamValue paramValue;


    private SqlMapperPlugin(Predicate<Object> predicate,
        ParamValue paramValue) {
      this.predicate = predicate;
      this.paramValue = paramValue;
    }


    //定义枚举插件
    static SqlMapperPlugin EnumSqlPlugin = of(Enum.class).paramValue((value, sql) ->
        Collections.singletonMap(sql, getEnumValue(value))
    );
    //定义Boolean插件
    static SqlMapperPlugin BooleanSqlPlugin = of(Boolean.class).paramValue((value, sql) ->
        Collections.singletonMap(sql, ((boolean) value) ? 1 : 0)
    );


    public static SqlMapperPlugin.MapperPluginsBuilder of(Predicate<Object> predicate) {
      return new MapperPluginsBuilder(predicate);
    }


    public static SqlMapperPlugin.MapperPluginsBuilder of(Class clazz) {
      return of((pd) -> {
        return clazz.isAssignableFrom(pd.getClass());
      });
    }


    boolean test(Object pd) {
      return this.predicate.test(pd);
    }


    Map<String, Object> getParams(String sql, Object value) {
      return paramValue.getParams(value, sql);
    }


    public static class MapperPluginsBuilder {


      Predicate<Object> predicate;


      public MapperPluginsBuilder(Predicate<Object> predicate) {
        this.predicate = predicate;
      }


      public SqlMapperPlugin paramValue(SqlMapperPlugin.ParamValue paramValue) {
        return new SqlMapperPlugin(this.predicate, paramValue);
      }
    }


    @FunctionalInterface
    public interface ParamValue {
      Map<String, Object> getParams(Object var1, String var2);
    }
  }


  public static String getEnumValue(Object value) {
    Method method;
    try {
      method = value.getClass()
          .getMethod("name");
      return String.valueOf(method.invoke(value));
    } catch (NoSuchMethodException e) {
      throw new RuntimeException("NoSuchMethodException", e);
    } catch (IllegalAccessException e) {
      throw new RuntimeException("IllegalAccessException", e);
    } catch (InvocationTargetException e) {
      throw new RuntimeException("InvocationTargetException", e);
    }
  }

主要用到了java8中新增的Predicate接口,用于判断value的Class类型,以及自己定义了一个FunctionalInterface 用于获取查询参数。这里先实现了EnumSqlPlugin,BooleanSqlPlugin俩个插件,之后有其他类型的需求,也可以通过类似的形式加入。对EnumSqlPlugin实现进行解释:

//定义枚举插件
    static SqlMapperPlugin EnumSqlPlugin = of(Enum.class).paramValue((value, sql) ->
        Collections.singletonMap(sql, getEnumValue(value))
    );

通过定义的of方法定义赋值Predicate,作为判断value是否为指定类型的方法。

public static SqlMapperPlugin.MapperPluginsBuilder of(Class clazz) {
      return of((pd) -> {
        return clazz.isAssignableFrom(pd.getClass());
      });
    }

of方法返回了MapperPluginsBuilder类,紧接着定义函数式接口paramValue的实现:

Collections.singletonMap(sql, getEnumValue(value))

最后返回EnumSqlPlugin对应的新实例:

return new SqlMapperPlugin(this.predicate, paramValue);

使用的时候,在Builder的构造函数中注入默认的插件即可,如日后有扩展,也可调用mapperPlugins方法动态加入:

private List<SqlMapperPlugin> sqlMapperPlugins;
 public Builder() {
      //添加基本类型默认的插件
      sqlMapperPlugins = Lists.newArrayList();
      this.mapperPlugins(SqlMapperPlugin.EnumSqlPlugin)
          .mapperPlugins(SqlMapperPlugin.BooleanSqlPlugin);
    }


public Builder mapperPlugins(SqlMapperPlugin sqlMapperPlugin)    {
      if (CollectionUtils.isEmpty(sqlMapperPlugins)) {
        sqlMapperPlugins = Lists.newArrayList();
      }
      sqlMapperPlugins.add(sqlMapperPlugin);
      return this;
    }

工具的使用

现在,我们可以使用封装好的工具了:

SqlWhereBuffer.Where where = SqlWhereBuffer.builder()
        .ifPresent(batchNumber, "batch_number=:batchNumber")
        .ifPresent(status, "upload_result=:uploadResult")
        .ifPresent(userId, "user_id=:userId")
        .limit(page * count, count)
        .orderBy("id")
        .asc();

这样,代码变得整洁多了,也符合java8函数式风格的效果。

    原文作者:李超
    原文地址: https://zhuanlan.zhihu.com/p/25044857
    本文转自网络文章,转载此文章仅为分享知识,如有侵权,请联系博主进行删除。

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