SQLHelper 代码细节

SQLHelper 具有如下功能：

1. 用于获取 sql.properties 配置文件中定义的 SQL 语句（模板）。
2. 生成基于单表的 SQL 语句。

以下是代码细节：

public class SQLHelper {

    private static final Properties sqlProperties = FileUtil.loadPropertiesFile("sql.properties");

    public static String getSQL(String key) {
        String value = "";
        if (sqlProperties.containsKey(key)) {
            value = sqlProperties.getProperty(key);
        } else {
            System.err.println("Can not get property [" + key + "] in sql.properties file.");
        }
        return value;
    }

    public static String generateSelectSQL(Class<?> cls, String condition, Object... params) {
        StringBuilder sql = new StringBuilder("select * from ");


        String tableName = getTableName(cls);
        if (StringUtil.isNotEmpty(tableName)) {
            sql.append(tableName).append(" ");
        }


        if (StringUtil.isNotEmpty(condition)) {
            if (ArrayUtil.isNotEmpty(params)) {
                condition = getWhereCondition(condition, params);
            }
            sql.append("where ").append(condition);
        }


        return sql.toString();
    }

    public static String generateInsertSQL(Class<?> cls, Map<String, Object> fieldMap) {
        StringBuilder sql = new StringBuilder("insert into ");

        String tableName = getTableName(cls);
        if (StringUtil.isNotEmpty(tableName)) {
            sql.append(tableName).append(" ");
        }

        if (MapUtil.isNotEmpty(fieldMap)) {
            int i = 0;
            StringBuilder columns = new StringBuilder();
            StringBuilder values = new StringBuilder(" values ");
            for (Map.Entry<String, ?> fieldEntry : fieldMap.entrySet()) {
                String columnName = StringUtil.toUnderline(fieldEntry.getKey());
                Object columnValue = fieldEntry.getValue();
                if (i == 0) {
                    columns.append("(").append(columnName);
                    values.append("('").append(columnValue).append("'");
                } else if (i == fieldMap.size() - 1) {
                    columns.append(", ").append(columnName).append(")");
                    values.append(", '").append(columnValue).append("')");
                } else {
                    columns.append(", ").append(columnName);
                    values.append(", '").append(columnValue).append("'");
                }
                i++;
            }
            sql.append(columns).append(values);
        }

        return sql.toString();
    }

    public static String generateDeleteSQL(Class<?> cls, String condition, Object... params) {
        StringBuilder sql = new StringBuilder("delete from ");

        String tableName = getTableName(cls);
        if (StringUtil.isNotEmpty(tableName)) {
            sql.append(tableName).append(" ");
        }

        if (StringUtil.isNotEmpty(condition)) {
            if (ArrayUtil.isNotEmpty(params)) {
                condition = getWhereCondition(condition, params);
            }
            sql.append(" where ").append(condition);
        }

        return sql.toString();
    }

    public static String generateUpdateSQL(Class<?> cls, Map<String, Object> fieldMap, String condition, Object... params) {
        StringBuilder sql = new StringBuilder("update ");

        String tableName = getTableName(cls);
        if (StringUtil.isNotEmpty(tableName)) {
            sql.append(tableName).append(" ");
        }

        if (MapUtil.isNotEmpty(fieldMap)) {
            sql.append("set ");
            int i = 0;
            for (Map.Entry<String, ?> fieldEntry : fieldMap.entrySet()) {
                String columnName = StringUtil.toUnderline(fieldEntry.getKey());
                Object columnValue = fieldEntry.getValue();
                if (i == 0) {
                    sql.append(columnName).append(" = '").append(columnValue).append("'");
                } else {
                    sql.append(", ").append(columnName).append(" = '").append(columnValue).append("'");
                }
                i++;
            }
        }

        if (StringUtil.isNotEmpty(condition)) {
            if (ArrayUtil.isNotEmpty(params)) {
                condition = getWhereCondition(condition, params);
            }
            sql.append(" where ").append(condition);
        }

        return sql.toString();
    }

    private static String getTableName(Class<?> cls) {
        String tableName;
        if (cls.isAnnotationPresent(Table.class)) {
            tableName = cls.getAnnotation(Table.class).value();
        } else {
            tableName = cls.getSimpleName().toLowerCase();
        }
        return tableName;
    }

    private static String getWhereCondition(String condition, Object... params) {
        StringBuffer buffer = new StringBuffer();
        Matcher matcher = Pattern.compile("\\?").matcher(condition);
        for (int i = 0; matcher.find(); i++) {
            matcher.appendReplacement(buffer, "'" + params[i].toString() + "'");
        }
        matcher.appendTail(buffer);
        return buffer.toString();
    }
}