利用反射实现orm

需求：从数据库表中查询数据，并且以json的格式输出

由于类中的属性太多了，不想一个一个写了，所以使用反射直接set进去，这样比较方便，也比较实用，并且加深了对反射的理解。

并且使用了jackson 将List转换成了 json格式的字符串

代码如下

public class test {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {
        Class.forName("com.mysql.jdbc.Driver");
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/book_shop?useSSL=false","root","111111");
 
        System.out.println("连接数据库成功");
 
        /**
         * 先查询图书的种类
         */
        Statement statement = null;
        statement= connection.createStatement();
        ResultSet resultSet = null;
        resultSet = statement.executeQuery("SELECT * FROM TB_CATEGORY");
        List<category> c = new ArrayList<>();
        while (resultSet.next()){
            category category = new category();
            category.setCategoryId(resultSet.getInt(1));
            category.setCategoryName(resultSet.getString(2));
            c.add(category);
        }
 
        /**
         * 利用反射，读取book里面的属性
         */
 
        Class clazz = Class.forName(Book.class.getName());
        Field[] fields = clazz.getDeclaredFields();
        List<String> fs = new ArrayList<>();
        for (Field f: fields) {
            fs.add(String.valueOf(f));
//            System.out.println(f);
        }
        /**
         * 使用流,将 属性名前面的去掉,留下简化的属性名
         */
        fs = fs.stream().map(x->x.replaceAll(x,x.split("\\.")[x.split("\\.").length-1])).collect(Collectors.toList());
//        System.out.println(fs);
 
        /**
         * 查询图书
         */
        String sql = "SELECT * FROM TB_BOOK";
        Statement st = null;
        st = connection.createStatement();
        ResultSet rs = null;
        rs = st.executeQuery(sql);
        ResultSetMetaData rd = rs.getMetaData();
        int count = rd.getColumnCount();
        List<Book> books = new ArrayList<>();
        while (rs.next()){
            int i = 1;
            Book book = new Book();
            while (i<count){
                //循环将数据库中的值set 到book类中
                String stringValue = rs.getString(i);
                String ColumnName = rd.getColumnName(i);
                setValues(ColumnName,stringValue,book,fs);
                //book中category代表数的种类,但是是用数字表示的,因此要转换成为name并且赋值
                if(ColumnName.equals("category_id")){
                    for(category category: c){
                        if(category.getCategoryId()==Integer.valueOf(stringValue)){
                            book.setCategory_name(category.getCategoryName());
                        }
                    }
                }
                i++;
            }
            books.add(book);
//            System.out.println();
        }
//        for(Book b:books){
//            System.out.println(b);
//        }
        /**
         * 利用jackson实现序列化
         */
        //创建映射对象
        ObjectMapper mapper = new ObjectMapper();
 
        try {
            String json = mapper.writeValueAsString(books);
            System.out.println(json);
        } catch (JsonProcessingException e) {
            e.printStackTrace();
        }
 
 
    }
 
    /**
     * 利用反射,调用 set方法
     * @param ColumnName
     * @param stringValue
     * @param book
     * @param fs
     * @throws ClassNotFoundException
     */
 
    public static void setValues(String ColumnName,String stringValue, Book book,List<String> fs) throws ClassNotFoundException {
 
        Class clazz = book.getClass();
        Field[] fields = clazz.getDeclaredFields();
        Field f = null;
        //我们这里要获得与之对应的属性,因为要调用set,必须得传参数进去,因此我们需要得到属性的类型
        for(Field field:fields ){
            if(ColumnName.equals(field.toString().split("\\.")[field.toString().split("\\.").length-1])){
                f = field;
                break;
            }
        }
        //准备拼接set方法,将属性名称前面改为大写
        String fileName = initStr(ColumnName);
        try {
 
            //拼接方法
            Method setBookValue = clazz.getDeclaredMethod("set"+fileName,f.getType());
//            System.out.println(f.getType());
            //book属性中有integer类型,因此需要判断并且转换类型
            if(f.getType().toString().equals("class java.lang.Integer")){
                setBookValue.invoke(book,Integer.valueOf(stringValue));
 
            }
            //同理,有int类型
            else if(f.getType().toString().equals("int")){
                setBookValue.invoke(book,Integer.valueOf(stringValue));
 
            }
            else{
                setBookValue.invoke(book,stringValue);
            }
 
 
        } catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
            e.printStackTrace();
        }
 
    }
 
    /**
     * 将首个字母大小写
     * @param old
     * @return
     */
    public static String initStr(String old){
        String str = old.substring(0,1).toUpperCase() + old.substring(1) ;
        return str ;
    }
 
} 

Book类

public class Book {
 
    Integer book_id;
    Integer category_id;//类别
    String category_name;//类别名称
    String book_name;
    String author;
    String publisher;
 
    int price;
    int sale_price;
    int amount;
 
    public Integer getBook_id() {
        return book_id;
    }
 
    public void setBook_id(Integer book_id) {
        this.book_id = book_id;
    }
 
    public Integer getCategory_id() {
        return category_id;
    }
 
    public void setCategory_id(Integer category_id) {
        this.category_id = category_id;
    }
 
    public String getCategory_name() {
        return category_name;
    }
 
    public void setCategory_name(String category_name) {
        this.category_name = category_name;
    }
 
    public String getBook_name() {
        return book_name;
    }
 
    public void setBook_name(String book_name) {
        this.book_name = book_name;
    }
 
    public int getSale_price() {
        return sale_price;
    }
 
    public void setSale_price(int sale_price) {
        this.sale_price = sale_price;
    }
 
    public String getAuthor() {
        return author;
    }
 
    public void setAuthor(String author) {
        this.author = author;
    }
 
    public String getPublisher() {
        return publisher;
    }
 
    public void setPublisher(String publisher) {
        this.publisher = publisher;
    }
 
    public int getPrice() {
        return price;
    }
 
    public void setPrice(int price) {
        this.price = price;
    }
 
 
 
    public int getAmount() {
        return amount;
    }
 
    public void setAmount(int amount) {
        this.amount = amount;
    }
 
    @Override
    public String toString() {
        return "Book{" +
                "book_id=" + book_id +
                ", category_id=" + category_id +
                ", category_name='" + category_name + '\'' +
                ", book_name='" + book_name + '\'' +
                ", author='" + author + '\'' +
                ", publisher='" + publisher + '\'' +
                ", price=" + price +
                ", sale_price=" + sale_price +
                ", amount=" + amount +
                '}';
    }
}

categorie 类

public class category {
    Integer categoryId;//类别
    String categoryName;//类别名称
 
    public Integer getCategoryId() {
        return categoryId;
    }
 
    public void setCategoryId(Integer categoryId) {
        this.categoryId = categoryId;
    }
 
    public String getCategoryName() {
        return categoryName;
    }
 
    public void setCategoryName(String categoryName) {
        this.categoryName = categoryName;
    }
 
    @Override
    public String toString() {
        return "category{" +
                "categoryId=" + categoryId +
                ", categoryName='" + categoryName + '\'' +
                '}';
    }
} 

__EOF__

本文作者：Reisen7
本文链接：https://www.cnblogs.com/reisen7/p/18547109.html
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