利用JAVA注解与反射 - 实现SQL语句自动生成

package com.ucky.annotation.hibernate; import java.lang.reflect.Field; import java.lang.reflect.Method; import java.util.Date; import java.util.HashMap; import java.util.Map; /** * 生成建表语句 */ public class SqlUtil { /* * 生成创建table语句 * */ public static String create(Class<?> clazz) { StringBuilder sb = new StringBuilder(); String tableName = getTableName(clazz); if (null == tableName || "".equals(tableName)) { return null; } sb.append("CREATE TABLE ").append(tableName).append("("); Map<String, String> columnMap = getColumn(clazz); for (Map.Entry<String, String> entry : columnMap.entrySet()) { sb.append(entry.getKey()); sb.append(" "); sb.append(entry.getValue()); sb.append(","); } sb.deleteCharAt(sb.length() - 1); sb.append(")"); return sb.toString(); } /* * 生成插入语句 * */ public static String insert(Class<?> clazz) { StringBuilder sb = new StringBuilder(); String tableName = getTableName(clazz); sb.append("INSERT INTO ").append(tableName).append(" ("); Map<String, String> columnMap = getColumn(clazz); for (Map.Entry<String, String> entry : columnMap.entrySet()) { sb.append(entry.getKey()); sb.append(","); } sb.deleteCharAt(sb.length() - 1); sb.append(") ").append("VALUES").append("("); for (int i = 0; i < columnMap.size(); i++) { sb.append("?").append(","); } sb.deleteCharAt(sb.length() - 1); sb.append(")"); return sb.toString(); } public static <T> String insert(Class<T> clazz , T entity){ String sql = insert(clazz); Field[] fields = entity.getClass().getDeclaredFields(); for(int i$ = 0; i$<fields.length; i$++){ try { //获取字段信息名 String value = getEntityValue(fields[i$].getName(),entity); sql = sql.replaceFirst("\\?",value); } catch (Exception e) { e.printStackTrace(); } } return sql; } /* * 通过id值进行修改 * */ public static <T> String updateById(Class<T> clazz , T entity){ StringBuilder sb = new StringBuilder(); sb.append("UPDATE ").append(getTableName(clazz)).append(" SET "); Field[] fields = entity.getClass().getDeclaredFields(); try { for(int i$ = 0 ; i$ < fields.length ; i$++){ if(!"id".equals(fields[i$].getName())){ sb.append(fields[i$].getName()); sb.append(" = "); sb.append(getEntityValue(fields[i$].getName(),entity)); sb.append(" ,"); } } sb.deleteCharAt(sb.length()-1); sb.append(" WHERE ").append("id = ").append(getEntityValue("id",entity)); } catch (Exception e) { throw new RuntimeException("获取值出现错误",e); } return sb.toString(); } public static <T> String deleteById(Class<T> clazz,T entity){ StringBuilder sb = new StringBuilder(); sb.append("DELETE FROM ").append(getTableName(clazz)).append(" WHERE "); try { sb.append("id = ").append(getEntityValue("id",entity)); } catch (Exception e) { throw new RuntimeException("获deleteById出现错误",e); } return sb.toString(); } /* * 获取表名称 * */ private static String getTableName(Class<?> clazz) { //判断是否为Table注释类型是方法返回true，否则返回false if (clazz.isAnnotationPresent(Table.class)) { //获取注解信息 Table table = clazz.getAnnotation(Table.class); if(!"".equals(table.name())){ return table.name(); } } return null; } /* * 获取字段信息的Map * */ private static Map<String, String> getColumn(Class<?> clazz) { Map<String, String> columns = new HashMap<String, String>(); //通过反射取得所有Field，因为table那里是注解指定的注解，类型，column是对应方法上的所以不能class.isAnnotationPresent直接判断 Field[] fields = clazz.getDeclaredFields(); if (fields != null) { String columnName, type; Column column; for (int i$ = 0; i$ < fields.length; i$++) { //判断当前field是否为Column注解 if (fields[i$].isAnnotationPresent(Column.class)) { //获取注解对象 column = fields[i$].getAnnotation(Column.class); columnName = column.name(); if("".equals(columnName)){ throw new RuntimeException("未找到对应字段名：" + i$); } //根据不同类型生成不同的SQL if (int.class.isAssignableFrom(fields[i$].getType())) { type = "int"; } else if (String.class.isAssignableFrom(fields[i$].getType())) { type = "String"; } else if (Date.class.isAssignableFrom(fields[i$].getType())) { type = "Date"; } else { throw new RuntimeException("不支持数据类型：" + fields[i$].getType().getSimpleName()); } type += (column.isNull() ? " " : " NOT NULL"); columns.put(columnName, type); } else if (fields[i$].isAnnotationPresent(PrimaryKey.class)) { PrimaryKey primaryKey = fields[i$].getAnnotation(PrimaryKey.class); //将一个类的成员变量置为private,其实我也不知道啥意思，有知道的指点一下 ，谢谢！ fields[i$].setAccessible(true); columnName = primaryKey.name(); if("".equals(columnName)){ throw new RuntimeException("未找到对应主键名" ); } type = "INT PRIMARY KEY AUTO_INCREMENT"; columns.put(columnName, type); } } } return columns; } private static <T> String getEntityValue(String columnName , T entity ) throws Exception{ String getMethodStr = columnName.substring(0,1).toUpperCase() + columnName.substring(1); Method method = entity.getClass().getMethod("get" + getMethodStr); return method.invoke(entity).toString(); } }