新人开发-JAVA 泛型CRUD-测试时 空指针。

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接口baseDao

import java.util.List;

public interface BaseDao<T> {
    public abstract void add(T t);
    public abstract void delete(T t);
    public abstract void update(T t);
    public abstract T select(T t);
    public abstract List<T>findAll();
}

实现BaseDaoImpl

import javax.jnlp.BasicService;
import java.lang.reflect.*;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;

import static oracle.net.aso.C00.t;

/**
 * Created by Administrator on 2017/1/4.
 */
public class BaseDaoImpl<T> implements BaseDao<T> {

    /** 操作常量 */
    public static final String SQL_INSERT = "insert";
    public static final String SQL_UPDATE = "update";
    public static final String SQL_DELETE = "delete";
    public static final String SQL_SELECT = "select";
    public static final String SQL_SELECTALL = "select";

    public Class<T> EntityClass; // 获取实体类

    public PreparedStatement statement;

    public String sql;

    public Object argType[];

    public ResultSet rs;

    @SuppressWarnings("unchecked")
    public BaseDaoImpl() {

        /**
         *  传递User就是 com.example.daoimp.BaseDaoImp<com.example.bean.User>
         *  传递Shop就是 com.example.daoimp.BaseDaoImp<com.example.bean.Shop>
         * */
//        ParameterizedType type = (ParameterizedType) getClass()
//                .getGenericSuperclass();

        /**
         * 这里如果传递的是User.那么就是class com.example.bean.User
         * 如果传递的是Shop.       那么就是class com.example.bean.Shop
         * */
//        EntityClass = (Class<T>) GenericsUtils.getSuperClassGenricType().getActualTypeArguments()[0];
        Class<T> EntityClass = GenericsUtils.getSuperClassGenricType(BasicService.class, 0);
    }

    @Override
    public void add(T t) {
        // TODO Auto-generated method stub
        sql = this.getSql(SQL_INSERT);   //获取sql.
        // 赋值.
        try {
            argType = setArgs(t, SQL_INSERT);
            statement = JdbcUtils.getPreparedStatement(sql);  //实例化PreparedStatement.
            //为sql语句赋值.
            statement = JdbcUtils.setPreparedStatementParam(statement,
                    argType);
            statement.executeUpdate(); //执行语句.
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            JdbcUtils.release(statement, null);  //释放资源.
        }
    }

    @Override
    public void delete(T t) {
        // TODO Auto-generated method stub
        sql = this.getSql(SQL_DELETE);
        try {
            argType = this.setArgs(t, SQL_DELETE);
            statement = JdbcUtils.getPreparedStatement(sql);
            statement = JdbcUtils.setPreparedStatementParam(statement,
                    argType);
            statement.executeUpdate();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            JdbcUtils.release(statement, null);
        }
    }

    @Override
    public void update(T t) {
        // TODO Auto-generated method stub
        sql = this.getSql(SQL_UPDATE);
        try {
            argType = setArgs(t, SQL_UPDATE);
            statement = JdbcUtils.getPreparedStatement(sql);
            statement = JdbcUtils.setPreparedStatementParam(statement,
                    argType);
            statement.executeUpdate();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            JdbcUtils.release(statement, null);
        }
    }

    @Override
    public T select(T t) {
        // TODO Auto-generated method stub
        sql = this.getSql(SQL_SELECT);
        T obj = null;
        try {
            argType = setArgs(t, SQL_SELECT);
            statement = JdbcUtils.getPreparedStatement(sql);
            statement = JdbcUtils.setPreparedStatementParam(statement,
                    argType);
            rs = statement.executeQuery();
            Field fields[] = EntityClass.getDeclaredFields();
            while (rs.next()) {
                obj = EntityClass.newInstance();
                for (int i = 0; i < fields.length; i++) {
                    fields[i].setAccessible(true);
                    fields[i].set(obj, rs.getObject(fields[i].getName()));
                }
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return obj;

    }
    @Override
    public List<T> findAll() {
        // TODO Auto-generated method stub
        sql = this.getSql(SQL_SELECTALL);
        List<T>list = new ArrayList<T>();
        T obj,t = null;
        try {
            argType = setArgs(t, SQL_SELECT);
            statement = JdbcUtils.getPreparedStatement(sql);
            statement = JdbcUtils.setPreparedStatementParam(statement,
                    argType);
            rs = statement.executeQuery();
            Field fields[] = EntityClass.getDeclaredFields();
            while (rs.next()) {
                obj = EntityClass.newInstance();
                for (int i = 0; i < fields.length; i++) {
                    fields[i].setAccessible(true);
                    fields[i].set(obj, rs.getObject(fields[i].getName()));
                }
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return list;
    }

    // sql拼接函数 形如 : insert into User(id,username,password,email,grade) values(?,?,?,?,?)
    private String getSql(String operator) {

        StringBuffer sql = new StringBuffer();
        // 通过反射获取实体类中的所有变量
        Field fields[] = EntityClass.getDeclaredFields();

        // 插入操作
        if (operator.equals(SQL_INSERT)) {
            sql.append("insert into " + EntityClass.getSimpleName());
            sql.append("(");
            for (int i = 0; fields != null && i < fields.length; i++) {
                fields[i].setAccessible(true);    //这句话必须要有,否则会抛出异常.
                String column = fields[i].getName();
                sql.append(column).append(",");
            }
            sql = sql.deleteCharAt(sql.length() - 1);
            sql.append(") values (");
            for (int i = 0; fields != null && i < fields.length; i++) {
                sql.append("?,");
            }
            sql.deleteCharAt(sql.length() - 1);
            // 是否需要添加分号
            sql.append(")");
        } else if (operator.equals(SQL_UPDATE)) {
            sql.append("update " + EntityClass.getSimpleName() + " set ");
            for (int i = 0; fields != null && i < fields.length; i++) {
                fields[i].setAccessible(true);
                String column = fields[i].getName();
                if (column.equals("id")) {
                    continue;
                }
                sql.append(column).append("=").append("?,");
            }
            sql.deleteCharAt(sql.length() - 1);
            sql.append(" where id=?");
        } else if (operator.equals(SQL_DELETE)) {
            sql.append("delete from " + EntityClass.getSimpleName()
                    + " where id=?");
        } else if (operator.equals(SQL_SELECT)) {
            sql.append("select * from " + EntityClass.getSimpleName()
                    + " where id=?");
        }else if (operator.equals(SQL_SELECTALL)) {
            sql.append("select * from " + EntityClass.getSimpleName()
                    );
        }
        return sql.toString();
    }

    // 获取参数.
    private Object[] setArgs(T entity, String operator)
            throws IllegalArgumentException, IllegalAccessException {

        Field fields[] = EntityClass.getDeclaredFields();
        if (operator.equals(SQL_INSERT)) {

            Object obj[] = new Object[fields.length];
            for (int i = 0; obj != null && i < fields.length; i++) {
                fields[i].setAccessible(true);
                obj[i] = fields[i].get(entity);
            }
            return obj;

        } else if (operator.equals(SQL_UPDATE)) {

            Object Tempobj[] = new Object[fields.length];
            for (int i = 0; Tempobj != null && i < fields.length; i++) {
                fields[i].setAccessible(true);
                Tempobj[i] = fields[i].get(entity);
            }

            Object obj[] = new Object[fields.length];
            System.arraycopy(Tempobj, 1, obj, 0, Tempobj.length - 1);
            obj[obj.length - 1] = Tempobj[0];
            return obj;

        } else if (operator.equals(SQL_DELETE)) {

            Object obj[] = new Object[1];
            fields[0].setAccessible(true);
            obj[0] = fields[0].get(entity);
            return obj;
        } else if (operator.equals(SQL_SELECT)) {

            Object obj[] = new Object[1];
            fields[0].setAccessible(true);
            obj[0] = fields[0].get(entity);
            return obj;
        }else if (operator.equals(SQL_SELECTALL)){
            Object obj[] = new Object[1];
            fields[0].setAccessible(true);
            obj[0] = fields[0].get(entity);
            return obj;
        }
        return null;
    }

}

实体类

测试类 Test
public class Test {
/**
* @param args
*/
public static void main(String args[]) throws SQLException {
// TODO Auto-generated method stub

List<Layer_tbl>list = null;
BaseDaoImpl imp = new BaseDaoImpl();
list = imp.findAll();
for(Layer_tbl layer_tbl:list){
System.out.println(layer_tbl.getLayerKeyID_grp()+" "+layer_tbl.getLayerId_grp()+" "+layer_tbl.getLayerElementID_grp()+" "+layer_tbl.getLayerPid_grp()+" "+layer_tbl.getProjectId_grp());
}

}
}
实体类Layer_tbl 字段在测试类里面有。字数限制就没贴。
然后测试的时候显示空指针

[qq_34052254]

反射工具类

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
 * Created by Administrator on 2017/1/4.
 */
public class GenericsUtils {
    /**
           * 通过反射,获得定义Class时声明的父类的范型参数的类型.
          * 如public BookManager extends GenricManager<Book>
          *
           * @param clazz The class to introspect
           * @return the first generic declaration, or <code>Object.class</code> if cannot be determined
     */
     public static Class getSuperClassGenricType(Class clazz) {
                return getSuperClassGenricType(clazz, 0);
            }

             /**
      * 通过反射,获得定义Class时声明的父类的范型参数的类型.
      * 如public BookManager extends GenricManager<Book>
              *     *
       * @param clazz clazz The class to introspect
       * @param index the Index of the generic ddeclaration,start from 0.
      */
             public static Class getSuperClassGenricType(Class clazz, int index) throws IndexOutOfBoundsException {

                 Type genType = clazz.getGenericSuperclass();

                if (!(genType instanceof ParameterizedType)) {
                         return Object.class;
                     }

                 Type[] params = ((ParameterizedType) genType).getActualTypeArguments();

                 if (index >= params.length || index < 0) {
                       return Object.class;
                    }
                 if (!(params[index] instanceof Class)) {
                        return Object.class;
                     }
                 return (Class) params[index];
            }
}

实体类

public class Layer_tbl {
    public int layerKeyID_grp;
    public int projectId_grp;
    public int layerPid_grp;
    public String layerElementID_grp;
    public String layerId_grp;

    public Layer_tbl(int layerKeyID_grp, int projectId_grp, int layerPid_grp, String layerElementID_grp, String layerId_grp) {
        this.layerKeyID_grp = layerKeyID_grp;
        this.projectId_grp = projectId_grp;
        this.layerPid_grp = layerPid_grp;
        this.layerElementID_grp = layerElementID_grp;
        this.layerId_grp = layerId_grp;
    }

    public Layer_tbl() {
    }

    public int getLayerKeyID_grp() {
        return layerKeyID_grp;
    }

    public void setLayerKeyID_grp(int layerKeyID_grp) {
        this.layerKeyID_grp = layerKeyID_grp;
    }

    public int getProjectId_grp() {
        return projectId_grp;
    }

    public void setProjectId_grp(int projectId_grp) {
        this.projectId_grp = projectId_grp;
    }

    public int getLayerPid_grp() {
        return layerPid_grp;
    }

    public void setLayerPid_grp(int layerPid_grp) {
        this.layerPid_grp = layerPid_grp;
    }

    public String getLayerElementID_grp() {
        return layerElementID_grp;
    }

    public void setLayerElementID_grp(String layerElementID_grp) {
        this.layerElementID_grp = layerElementID_grp;
    }

    public String getLayerId_grp() {
        return layerId_grp;
    }

    public void setLayerId_grp(String layerId_grp) {
        this.layerId_grp = layerId_grp;
    }
}

[尼古拉斯-全蛋]

空指针报到哪一行了

[qq_34052254]

这个泛型CRUD是网上查找的。最开始的时候是获取类转型错误。用了工具类之后报了空指针。 使用的事maven 和SPring MVC

[qq_34052254]

引用 2 楼 qnmdcsdn 的回复:

空指针报到哪一行了

[尼古拉斯-全蛋]

// EntityClass = (Class<T>) GenericsUtils.getSuperClassGenricType().getActualTypeArguments()[0]; Class<T> EntityClass = GenericsUtils.getSuperClassGenricType(BasicService.class, 0); 标红的去掉

[qq_34052254]

引用 5 楼 qnmdcsdn 的回复:

// EntityClass = (Class<T>) GenericsUtils.getSuperClassGenricType().getActualTypeArguments()[0];
Class<T> EntityClass = GenericsUtils.getSuperClassGenricType(BasicService.class, 0);

标红的去掉

又出现了下标越界的问题。。其实我不太懂这个方法

[尼古拉斯-全蛋]

打断点看下fields得到值没

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引用 7 楼 qnmdcsdn 的回复:

打断点看下fields得到值没

在哪打断点-_- 萌新刚学到框架。还没打过断点做测试

[尼古拉斯-全蛋]

引用 8 楼 qq_34052254 的回复:

[quote=引用 7 楼 qnmdcsdn 的回复:] 打断点看下fields得到值没

在哪打断点-_- 萌新刚学到框架。还没打过断点做测试[/quote] Field fields[] = EntityClass.getDeclaredFields(); 刚上来就玩这，玩的有点大啊，打到上边那一行

[qq_34052254]

引用 7 楼 qnmdcsdn 的回复:

打断点看下fields得到值没

而且在测试 添加新数据的方法时 也报错了-_-.

[qq_34052254]

引用 9 楼 qnmdcsdn 的回复:

[quote=引用 8 楼 qq_34052254 的回复:] [quote=引用 7 楼 qnmdcsdn 的回复:] 打断点看下fields得到值没

在哪打断点-_- 萌新刚学到框架。还没打过断点做测试[/quote] Field fields[] = EntityClass.getDeclaredFields(); 刚上来就玩这，玩的有点大啊，打到上边那一行[/quote] 还好吧。因为代码的意思和逻辑我都能看明白。而且这属于基础的泛型吧。想通过这个做一个通用的CRUD以后就不用再自己敲了

[尼古拉斯-全蛋]

引用 10 楼 qq_34052254 的回复:

[quote=引用 7 楼 qnmdcsdn 的回复:] 打断点看下fields得到值没

而且在测试 添加新数据的方法时 也报错了-_-.[/quote] 很明显，这是sql拼错了，打印出来看看

[qq_34052254]

引用 7 楼 qnmdcsdn 的回复:

打断点看下fields得到值没

没拿到值 好像是Entityclass开始就没拿到类。所以后面后面再sql执行的时候Object都没有赋值。 sql语句 比如说 全部展示 还是"select * from Object"

[qq_34052254]

引用 12 楼 qnmdcsdn 的回复:

[quote=引用 10 楼 qq_34052254 的回复:] [quote=引用 7 楼 qnmdcsdn 的回复:] 打断点看下fields得到值没

而且在测试 添加新数据的方法时 也报错了-_-.[/quote] 很明显，这是sql拼错了，打印出来看看[/quote]这个SQL出错时因为OBJECT没拿到值。

[qq_34052254]

引用 12 楼 qnmdcsdn 的回复:

[quote=引用 10 楼 qq_34052254 的回复:]
[quote=引用 7 楼 qnmdcsdn 的回复:]
打断点看下fields得到值没

而且在测试 添加新数据的方法时 也报错了-_-.[/quote]

很明显，这是sql拼错了，打印出来看看[/quote]


EntityClass没拿到 然后field 取不到值 然后sql语句也没取对