tk.mapper 原理解讀

一個簡單的類TK.MAPPER實現

mybatis支持@Insert與@InsertProvider註解。這兩個註解的實現以下：
入口

void parseStatement(Method method) {
    Class<?> parameterTypeClass = getParameterType(method);
    LanguageDriver languageDriver = getLanguageDriver(method);
    //解析出SQL
    SqlSource sqlSource = getSqlSourceFromAnnotations(method, parameterTypeClass, languageDriver);
    if (sqlSource != null) {
      Options options = method.getAnnotation(Options.class);
      final String mappedStatementId = type.getName() + "." + method.getName();
      Integer fetchSize = null;
      Integer timeout = null;
      StatementType statementType = StatementType.PREPARED;
      ResultSetType resultSetType = ResultSetType.FORWARD_ONLY;
      SqlCommandType sqlCommandType = getSqlCommandType(method);
      boolean isSelect = sqlCommandType == SqlCommandType.SELECT;
      boolean flushCache = !isSelect;
      boolean useCache = isSelect;

private SqlSource getSqlSourceFromAnnotations(Method method, Class<?> parameterType, LanguageDriver languageDriver) {
    try {
      Class<? extends Annotation> sqlAnnotationType = getSqlAnnotationType(method);
      Class<? extends Annotation> sqlProviderAnnotationType = getSqlProviderAnnotationType(method);
      if (sqlAnnotationType != null) {
        if (sqlProviderAnnotationType != null) {
          throw new BindingException("You cannot supply both a static SQL and SqlProvider to method named " + method.getName());
        }
       //解析@Insert
        Annotation sqlAnnotation = method.getAnnotation(sqlAnnotationType);
        final String[] strings = (String[]) sqlAnnotation.getClass().getMethod("value").invoke(sqlAnnotation);
        return buildSqlSourceFromStrings(strings, parameterType, languageDriver);
      } else if (sqlProviderAnnotationType != null) {
        //解析@InsertProvider
        Annotation sqlProviderAnnotation = method.getAnnotation(sqlProviderAnnotationType);
        return new ProviderSqlSource(assistant.getConfiguration(), sqlProviderAnnotation, type, method);
      }
      return null;
    } catch (Exception e) {
      throw new BuilderException("Could not find value method on SQL annotation.  Cause: " + e, e);
    }
  }

經過代碼發現@Insert解析，相似於XML文件形式，至關於將XML文件的類容寫到JAVA裏面。@InsertProvider是在執行SQL語句的時候，把參數給你，由你本身來解析出SQL語句。相對於@Insert 第二種更靈活一些。 看看是怎麼調用你寫的方法的：

private SqlSource createSqlSource(Object parameterObject) {
    try {
      int bindParameterCount = providerMethodParameterTypes.length - (providerContext == null ? 0 : 1);
      String sql;
      if (providerMethodParameterTypes.length == 0) {
        sql = (String) providerMethod.invoke(providerType.newInstance());
      } else if (bindParameterCount == 0) {
        sql = (String) providerMethod.invoke(providerType.newInstance(), providerContext);
      } else if (bindParameterCount == 1 &&
              (parameterObject == null || providerMethodParameterTypes[(providerContextIndex == null || providerContextIndex == 1) ? 0 : 1].isAssignableFrom(parameterObject.getClass()))) {
        sql = (String) providerMethod.invoke(providerType.newInstance(), extractProviderMethodArguments(parameterObject));
      } else if (parameterObject instanceof Map) {
        @SuppressWarnings("unchecked")
        Map<String, Object> params = (Map<String, Object>) parameterObject;
        sql = (String) providerMethod.invoke(providerType.newInstance(), extractProviderMethodArguments(params, providerMethodArgumentNames));
      } else {
        throw new BuilderException("Error invoking SqlProvider method ("
                + providerType.getName() + "." + providerMethod.getName()
                + "). Cannot invoke a method that holds "
                + (bindParameterCount == 1 ? "named argument(@Param)": "multiple arguments")
                + " using a specifying parameterObject. In this case, please specify a 'java.util.Map' object.");
      }
      Class<?> parameterType = parameterObject == null ? Object.class : parameterObject.getClass();
      return sqlSourceParser.parse(replacePlaceholder(sql), parameterType, new HashMap<String, Object>());
    } catch (BuilderException e) {
      throw e;
    } catch (Exception e) {
      throw new BuilderException("Error invoking SqlProvider method ("
          + providerType.getName() + "." + providerMethod.getName()
          + ").  Cause: " + e, e);
    }
  }

一個例子:

public interface MyMapper {

    @InsertProvider(type=MyMapperImpl.class,method = "insertSelect")
    public void insertSelect(String s1, ChannelOrders channelOrders);
}

實現

public class MyMapperImpl {

    public String insertSelect(ProviderContext pc,Object agrs){
        Class clazz = pc.getMapperType();
        System.out.println("xxxx");
        return "select 1";
    }
}

這是一個簡單的例子，但也是tk.mapper的原理。

tk.mapper

TK是在初始化完畢的時候，替換掉原有的SqlSource.

public void setSqlSource(MappedStatement ms) throws Exception {
        if (this.mapperClass == getMapperClass(ms.getId())) {
            throw new MapperException("請不要配置或掃描通用Mapper接口類：" + this.mapperClass);
        }
        Method method = methodMap.get(getMethodName(ms));
        try {
            //第一種，直接操做ms，不須要返回值
            if (method.getReturnType() == Void.TYPE) {
                method.invoke(this, ms);
            }
            //第二種，返回SqlNode
            else if (SqlNode.class.isAssignableFrom(method.getReturnType())) {
                SqlNode sqlNode = (SqlNode) method.invoke(this, ms);
                DynamicSqlSource dynamicSqlSource = new DynamicSqlSource(ms.getConfiguration(), sqlNode);
                setSqlSource(ms, dynamicSqlSource);
            }
            //第三種，返回xml形式的sql字符串
            else if (String.class.equals(method.getReturnType())) {
                String xmlSql = (String) method.invoke(this, ms);
                SqlSource sqlSource = createSqlSource(ms, xmlSql);
                //替換原有的SqlSource
                setSqlSource(ms, sqlSource);
            } else {
                throw new MapperException("自定義Mapper方法返回類型錯誤,可選的返回類型爲void,SqlNode,String三種!");
            }
        } catch (IllegalAccessException e) {
            throw new MapperException(e);
        } catch (InvocationTargetException e) {
            throw new MapperException(e.getTargetException() != null ? e.getTargetException() : e);
        }
    }

下面咱們看一下InsertSelect的生成原理

public String insertSelective(MappedStatement ms) {
        Class<?> entityClass = getEntityClass(ms);
        StringBuilder sql = new StringBuilder();
        //獲取所有列
        Set<EntityColumn> columnList = EntityHelper.getColumns(entityClass);
        //Identity列只能有一個
        Boolean hasIdentityKey = false;
        //先處理cache或bind節點
        for (EntityColumn column : columnList) {
            if (!column.isInsertable()) {
                continue;
            }
            if (StringUtil.isNotEmpty(column.getSequenceName())) {
                //sql.append(column.getColumn() + ",");
            } else if (column.isIdentity()) {
                //這種狀況下,若是原先的字段有值,須要先緩存起來,不然就必定會使用自動增加
                //這是一個bind節點
                sql.append(SqlHelper.getBindCache(column));
                //若是是Identity列，就須要插入selectKey
                //若是已經存在Identity列，拋出異常
                if (hasIdentityKey) {
                    //jdbc類型只須要添加一次
                    if (column.getGenerator() != null && column.getGenerator().equals("JDBC")) {
                        continue;
                    }
                    throw new MapperException(ms.getId() + "對應的實體類" + entityClass.getCanonicalName() + "中包含多個MySql的自動增加列,最多隻能有一個!");
                }
                //插入selectKey
                SelectKeyHelper.newSelectKeyMappedStatement(ms, column, entityClass, isBEFORE(), getIDENTITY(column));
                hasIdentityKey = true;
            } else if (column.isUuid()) {
                //uuid的狀況，直接插入bind節點
                sql.append(SqlHelper.getBindValue(column, getUUID()));
            }
        }
        sql.append(SqlHelper.insertIntoTable(entityClass, tableName(entityClass)));
        sql.append("<trim prefix=\"(\" suffix=\")\" suffixOverrides=\",\">");
        for (EntityColumn column : columnList) {
            if (!column.isInsertable()) {
                continue;
            }
            if (StringUtil.isNotEmpty(column.getSequenceName()) || column.isIdentity() || column.isUuid()) {
                sql.append(column.getColumn() + ",");
            } else {
                sql.append(SqlHelper.getIfNotNull(column, column.getColumn() + ",", isNotEmpty()));
            }
        }
        sql.append("</trim>");
        sql.append("<trim prefix=\"VALUES(\" suffix=\")\" suffixOverrides=\",\">");
        for (EntityColumn column : columnList) {
            if (!column.isInsertable()) {
                continue;
            }
            //優先使用傳入的屬性值,當原屬性property!=null時，用原屬性
            //自增的狀況下,若是默認有值,就會備份到property_cache中,因此這裏須要先判斷備份的值是否存在
            if (column.isIdentity()) {
                sql.append(SqlHelper.getIfCacheNotNull(column, column.getColumnHolder(null, "_cache", ",")));
            } else {
                //其餘狀況值仍然存在原property中
                sql.append(SqlHelper.getIfNotNull(column, column.getColumnHolder(null, null, ","), isNotEmpty()));
            }
            //當屬性爲null時，若是存在主鍵策略，會自動獲取值，若是不存在，則使用null
            //序列的狀況
            if (StringUtil.isNotEmpty(column.getSequenceName())) {
                sql.append(SqlHelper.getIfIsNull(column, getSeqNextVal(column) + " ,", isNotEmpty()));
            } else if (column.isIdentity()) {
                sql.append(SqlHelper.getIfCacheIsNull(column, column.getColumnHolder() + ","));
            } else if (column.isUuid()) {
                sql.append(SqlHelper.getIfIsNull(column, column.getColumnHolder(null, "_bind", ","), isNotEmpty()));
            }
        }
        sql.append("</trim>");
        return sql.toString();
    }

能夠看到tk.mapper生成的SQL語句和XML同樣。