Java 在将resultset动态转换为JSON时处理空值
我正在使用以下方法将resultset转换为JSON,并试图根据下面描述的场景找出如何处理Java 在将resultset动态转换为JSON时处理空值,java,Java,我正在使用以下方法将resultset转换为JSON,并试图根据下面描述的场景找出如何处理null值: 在Oracle SQL developer中运行以下SQL查询(在下面的代码中使用)时: 从EMP中选择SQLQUERY,其中id=6,我得到以下结果: Employee State of Residence Employee Count 1 (null) 1400 2 AL
null
值:
在Oracle SQL developer中运行以下SQL查询(在下面的代码中使用)时:
从EMP中选择SQLQUERY,其中id=6
,我得到以下结果:
Employee State of Residence Employee Count
1 (null) 1400
2 AL 1200
3 MS 6700
4 WT 4
如上所述,对于上述SQL查询返回的上述数据,下面的Java代码将其转换为以下JSON:
[{
"Employee Count": " 1400"
},
{
"Employee Count": " 1200",
"Employee State of Residence": "AL"
},
{
"Employee Count": " 6700",
"Employee State of Residence": "MS"
},
{
"Employee Count": " 4",
"Employee State of Residence": "WT"
}
]
因此,基本上,它没有在上面员工计数1400
的JSON响应中显示Employee State of Residence
列名,因为它是null
。我如何确保在null
值的情况下
显示可能包含空字符串的列名?或者,如果NULL
,我应该让数据库人员返回一些内容吗
@Override
public String getData(Integer id) throws DaoException {
DataSource ds = null;
Connection conn = null;
PreparedStatement pstmt = null;
PreparedStatement pstmtNew = null;
ResultSet rs = null;
ResultSet rsNew = null;
JSONArray json = new JSONArray();
try {
ds = jdbcTemplate.getDataSource();
conn = ds.getConnection();
pstmt = conn.prepareStatement("SELECT SQLQUERY FROM EMP WHERE id = ?");
pstmt.setInt(1, id);
rs = pstmt.executeQuery();
rs.next();
String sqlQuery = rs.getString("SQLQUERY");
pstmtNew = conn.prepareStatement(sqlQuery);
rsNew = pstmtNew.executeQuery();
ResultSetMetaData rsmd = rsNew.getMetaData();
int cols = rsmd.getColumnCount();
logger.info("Total Column Count "+rsmd.getColumnCount());
logger.info("The query fetched %d columns\n",cols);
logger.info("These columns are: ");
for (int i=1;i<=cols;i++) {
String colName = rsmd.getColumnName(i);
String colType = rsmd.getColumnTypeName(i);
logger.info(colName+" of type "+colType);
}
while(rsNew.next()) {
JSONObject obj = new JSONObject();
for (int i=1;i<=cols;i++) {
String column_name = rsmd.getColumnName(i);
if (rsmd.getColumnType(i) == java.sql.Types.ARRAY) {
obj.put(column_name, rsNew.getArray(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.BIGINT) {
obj.put(column_name, rsNew.getInt(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.BOOLEAN) {
obj.put(column_name, rsNew.getBoolean(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.BLOB) {
obj.put(column_name, rsNew.getBlob(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.DOUBLE) {
obj.put(column_name, rsNew.getDouble(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.FLOAT) {
obj.put(column_name, rsNew.getFloat(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.INTEGER) {
obj.put(column_name, rsNew.getInt(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.NVARCHAR) {
obj.put(column_name, rsNew.getNString(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.VARCHAR) {
obj.put(column_name, rsNew.getString(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.TINYINT) {
obj.put(column_name, rsNew.getInt(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.SMALLINT) {
obj.put(column_name, rsNew.getInt(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.DATE) {
obj.put(column_name, rsNew.getDate(column_name));
} else if (rsmd.getColumnType(i) == java.sql.Types.TIMESTAMP) {
obj.put(column_name, rsNew.getTimestamp(column_name));
} else {
obj.put(column_name, rsNew.getObject(column_name));
}
}
json.put(obj);
}
}
catch(Throwable th) {
throw new DaoException(th.getMessage(), th);
}
finally {
if (rs != null) { try { rs.close(); } catch (SQLException e) { e.printStackTrace(); }}
if (rsNew != null) { try { rsNew.close(); } catch (SQLException e) { e.printStackTrace(); }}
if (pstmt != null) { try { pstmt.close(); } catch(SQLException sqe) { sqe.printStackTrace(); }}
if (pstmtNew != null) { try { pstmtNew.close(); } catch(SQLException sqe) { sqe.printStackTrace(); }}
if (conn != null) { try { conn.close(); } catch (SQLException sqle) { sqle.printStackTrace(); }}
}
return json.toString();
}
看看这是否有助于您:
else if(rsmd.getColumnType(i) == java.sql.Types.VARCHAR) {
//Handle the column "Employee State of Residence" differently
if(column_name.equals("Employee State of Residence")){
String stateValue = rsNew.getString(column_name);
obj.put(column_name, stateValue==null?"":stateValue );
}else{
//Else do it the regular way
obj.put(column_name, rsNew.getString(column_name));
}
}
这是JSONObject中的一个限制的结果。为了查看JSON对象中的条目,需要放置一个JSONObject.NULL。我将尝试将您的代码修改为以下内容:
} else {
Object object = rsNew.getObject(column_name);
if (object != null) {
obj.put(column_name, rsNew.getObject(column_name));
} else {
obj.put(column_name, JSONObject.NULL);
}
}
根据您使用的JSON库和版本的不同,这可能会有所不同。请在您的问题中包含这些详细信息。难道您不能简单地检查您上面编写的代码中的null并输出一个空字符串吗?您能告诉我在哪里以及如何进行吗?我有点困惑。谢谢你不会更容易吧?它有一个选项。@RobertHarvey我在
else if(rsmd.getColumnType(I)=java.sql.Types.VARCHAR)
中使用了这些代码行来显式检查空值if(rsNew.getString(column_name)==null){obj.put(column_name,”;}else{obj.put(column_name,rsNew.getString)(column_name));}
这是您在第一条评论中提到的吗?在添加此显式检查后,它会起作用。我可能还必须为其他人执行此显式检查。是的,这就是我的意思。谢谢。但我可能不想在此处硬编码列名,因为对于不同的SQL查询,我可能会遇到类似的问题
} else {
Object object = rsNew.getObject(column_name);
if (object != null) {
obj.put(column_name, rsNew.getObject(column_name));
} else {
obj.put(column_name, JSONObject.NULL);
}
}