创建通用接口

在通用接口中使用@InsertProvider,@UpdateProvider,@DeleteProvider,@SelectProvider注解配置增删改查的类和方法，并添加通用方法

public interface BaseMapper {    @InsertProvider(type = BaseMapperProvider.class, method = "insert")    int insert(T entity);    @DeleteProvider(type = BaseMapperProvider.class, method = "deleteByPrimary")    int deleteByPrimary(E id);    @DeleteProvider(type = BaseMapperProvider.class, method = "delete")    int delete(@Param("wrapper") Wrapper wrapper);    @UpdateProvider(type = BaseMapperProvider.class, method = "updateByPrimary")    int updateByPrimary(T entity);    @DeleteProvider(type = BaseMapperProvider.class, method = "update")    int update(@Param("entity") T entity, @Param("wrapper") Wrapper wrapper);    @SelectProvider(type = BaseMapperProvider.class, method = "selectByPrimary")    T selectByPrimary(@Param("id") E id);    @SelectProvider(type = BaseMapperProvider.class, method = "select")    T selectOne(@Param("wrapper") Wrapper wrapper);    @SelectProvider(type = BaseMapperProvider.class, method = "select")    List select();    @SelectProvider(type = BaseMapperProvider.class, method = "select")    List selectList(@Param("wrapper") Wrapper wrapper);}

自定义注解

通过注解配置表的一些信息

1.@Table 配置表

@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.TYPE)public @interface Table {/**     * 配置表名     *     * @return 表名     */    String value() default "";}

2.@Column 配置字段

@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.FIELD)public @interface Column {      /**     * 配置字段名称     *     * @return 字段名称     */    String value() default "";      /**     * 配置字段排序     *     * @return 字段排序     */    boolean order() default false;      /**     * 配置字段排序类型     *     * @return 段排序类型     */    String orderType() default "desc";}

3.@JoinColumn 配置关联表

@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.FIELD)public @interface JoinColumn {      /**     * 配置要关联的表     *     * @return 表名     */    String tableName();      /**     * 配置字段名称     *     * @return 字段名称     */    String column() default "";      /**     * 配置两表之间的关系     *     * @return 两表之间的关系     */    Association[] relations();}

4.@Association 配置两表之间的关系

public @interface Association {    /**     * 配置当前表字段名称     *     * @return 当前表字段名称     */    String target();    /**     * 配置关联表字段名称     *     * @return 关联表字段名称     */    String association();}

5.@Primary 配置主键

@Retention(RetentionPolicy.RUNTIME)@Target(ElementType.FIELD)public @interface Primary {      /**     * 配置主键     *     * @return 是否是主键     */    boolean value() default true;}

3.编写BaseMapperProvider通过注解动态拼接SQL

这个类的方法可以加入ProviderContext类型的参数，可以通过 ProviderContext 来获取mapper的信息，通过泛型获取实体，通过注解动态生成SQL

public class BaseMapperProvider {    /**     * 用来缓存已经生成的SQL     */    private static final Map CONTEXT = new ConcurrentHashMap<>();    public String insert(ProviderContext context) {        return getSqlBuilder(context).insert().build();    }    public String deleteByPrimary(Object o, ProviderContext context) {        return getSqlBuilder(context).select().byPrimary().build();    }    public String delete(Wrapper wrapper, ProviderContext context) {        return getSqlBuilder(context).delete().where(wrapper).build();    }    public String updateByPrimary(Object o, ProviderContext context) {        return getSqlBuilder(context).update().byPrimary().build();    }    public String update(Object entity, Wrapper wrapper, ProviderContext context) {        return getSqlBuilder(context).update().where(wrapper).build();    }    public String select(Wrapper wrapper, ProviderContext context) {        return getSqlBuilder(context).select().where(wrapper).build();    }    public String selectByPrimary(Object o, ProviderContext context) {        return getSqlBuilder(context).select().byPrimary().build();    }    private Class getEntityType(ProviderContext context) {        return (Class) ((ParameterizedType) (context.getMapperType().getGenericInterfaces()[0])).getActualTypeArguments()[0];    }    private SQLBuilder getSqlBuilder(ProviderContext context) {        String name = getEntityType(context).getName();        SQLBuilder sqlBuilder = CONTEXT.get(name);        if (sqlBuilder == null) {            sqlBuilder = new SQLBuilder(getEntityType(context));            CONTEXT.put(name, sqlBuilder);        }        return sqlBuilder.reset();    }}

4.动态SQL类编写

public class SQLBuilder {    private final TableInfo tableInfo;    private final Class> type;    private SQL sql;    public SQLBuilder(Class> type) {        this.tableInfo = new TableInfo(type);        this.type = type;    }    public SQLBuilder reset() {        sql = new SQL();        return this;    }    public SQLBuilder insert() {        List columns = tableInfo.getColumns();        sql.INSERT_INTO(getTableName());        StringBuilder value = new StringBuilder();        StringBuilder values = new StringBuilder();        for (int i = 0; i < columns.size(); i++) {            ColumnInfo columnInfo = columns.get(i);            String columnName = columnInfo.getColumnName();            String fieldName = columnInfo.getFieldName();            String separator = ",";            if (i + 1 == columns.size()) {                separator = "";            }            value.append(ifScript(fieldName, columnName, separator));            values.append(ifScript(fieldName, sharp(fieldName), separator));        }        sql.VALUES(getPrimaryColumnName(), sharp(getPrimaryFieldName()));        sql.VALUES(value.toString(), values.toString());        return this;    }    public SQLBuilder delete() {        sql.DELETE_FROM(getTableName());        return this;    }    public SQLBuilder update() {        List columns = tableInfo.getColumns();        sql.UPDATE(getTableName());        StringBuilder set = new StringBuilder();        for (int i = 0; i < columns.size(); i++) {            ColumnInfo columnInfo = columns.get(i);            String fieldName = columnInfo.getFieldName();            String columnName = columnInfo.getColumnName();            String separator = ",";            if (i + 1 == columns.size()) {                separator = "";            }            set.append(ifScript(fieldName, set(columnName, fieldName), separator));        }        sql.SET(set.toString());        return this;    }    public SQLBuilder select() {        String tableName = getTableName();        sql.SELECT(select(tableName, getPrimaryColumnName(), getPrimaryFieldName()));        for (ColumnInfo columnInfo : tableInfo.getColumns()) {            sql.SELECT(select(tableName, columnInfo.getColumnName(), columnInfo.getFieldName()));        }        sql.FROM(tableName);        for (JoinColumnInfo joinColumnInfo : tableInfo.getJoinColumns()) {            String joinTableName = joinColumnInfo.getTableName();            sql.FROM(joinTableName);            sql.SELECT(select(joinTableName, joinColumnInfo.getColumnName(), joinColumnInfo.getFieldName()));            List associations = joinColumnInfo.getAssociations();            for (AssociationInfo associationInfo : associations) {                sql.WHERE(condition(tableName, associationInfo.getTarget(), joinTableName, associationInfo.getAssociation()));            }        }        return this;    }    public SQLBuilder byPrimary() {        sql.WHERE(condition(getTableName(), getPrimaryColumnName(), "id"));        return this;    }    public SQLBuilder where(Wrapper wrapper) {        if (wrapper != null) {            List conditions = wrapper.getConditions();            for (Condition condition : conditions) {                if (condition.isAnd()) {                    sql.AND();                }                if (!condition.isAnd()) {                    sql.OR();                }                sql.WHERE(condition.render());            }        }        return this;    }    public TableInfo getTableInfo() {        return tableInfo;    }    public Class> getType() {        return type;    }    private String getTableName() {        return tableInfo.getTableName();    }    private PrimaryInfo getPrimaryInfo() {        return tableInfo.getPrimaryInfo();    }    private String getPrimaryColumnName() {        return getPrimaryInfo().getColumnName();    }    private String getPrimaryFieldName() {        return getPrimaryInfo().getFieldName();    }    private String select(String tableName, String columnName, String fieldName) {        return String.format("%s.%s "%s"", tableName, columnName, fieldName);    }    private String sharp(String fieldName) {        return String.format("#{%s}", fieldName);    }    private String set(String columnName, String fieldName) {        return String.format("%s = #{%s}", columnName, fieldName);    }    private String ifScript(String fieldName, String content, String separator) {        return String.format("%s%s", fieldName, fieldName, content, separator);    }    private String condition(String tableName, String columnName, String fieldName) {        return String.format("%s.%s = #{%s}", tableName, columnName, fieldName);    }    private String condition(String tableName, String left, String joinTableName, String right) {        return String.format("%s.%s = %s.%s", tableName, left, joinTableName, right);    }    /**     * ";    }}

有几个对应注解的实体我就不粘了，这些代码只是给大家提供些思路，这种方式是完全支持xml写法的，具体实现可以看看这个项目

https://gitee.com/931942788/common-mapper