如何转换成一个Java的ResultSet成JSON? [英] How to convert a Java resultset into JSON?
问题描述
我有一个结果作为使用JDBC连接一个MySQL查询的结果。所以,我的工作是把结果集转换成JSON格式。所以,我可以将它发送到客户方作为Ajax响应。有些人能够解释如何做转换成JSON格式,因为我是新来的Java和以及JSON的概念
I have a resultset as a result of a MySQL query using the JDBC connector. So my job is to convert the resultset into a JSON format. So that I can send it to the clientside as a AJAX response. Can some one explain how to do the conversion to JSON format as I am new to both Java and as well as the concept of JSON
推荐答案
如果您使用的是JSON我推荐的杰克逊JSON库。
If you are using JSON I recommend the Jackson JSON library.
http://wiki.fasterxml.com/JacksonHome
JAR文件可以在这里找到:
The jar files can be found here:
http://wiki.fasterxml.com/JacksonDownload
下面是一般的code我用转换任何结果集为一个地图<>或者List<地图<>>使用JacksonJSON是pretty的直线前进(见下文)转换为JSON
Here is the generic code I use to convert any result set into a Map<> or List< Map<> > Converting this to JSON using JacksonJSON is pretty straight forward (See Below).
package com.naj.tmoi.entity;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class EntityFactory {
public EntityFactory(Connection connection, String queryString) {
this.queryString = queryString;
this.connection = connection;
}
public Map<String, Object> findSingle(Object[] params) throws SQLException {
List<Map<String, Object>> objects = this.findMultiple(params);
if (objects.size() != 1) {
throw new SQLException("Query did not produce one object it produced: " + objects.size() + " objects.");
}
Map<String, Object> object = objects.get(0); //extract only the first item;
return object;
}
public List<Map<String, Object>> findMultiple(Object[] params) throws SQLException {
ResultSet rs = null;
PreparedStatement ps = null;
try {
ps = this.connection.prepareStatement(this.queryString);
for (int i = 0; i < params.length; ++i) {
ps.setObject(1, params[i]);
}
rs = ps.executeQuery();
return getEntitiesFromResultSet(rs);
} catch (SQLException e) {
throw (e);
} finally {
if (rs != null) {
rs.close();
}
if (ps != null) {
ps.close();
}
}
}
protected List<Map<String, Object>> getEntitiesFromResultSet(ResultSet resultSet) throws SQLException {
ArrayList<Map<String, Object>> entities = new ArrayList<>();
while (resultSet.next()) {
entities.add(getEntityFromResultSet(resultSet));
}
return entities;
}
protected Map<String, Object> getEntityFromResultSet(ResultSet resultSet) throws SQLException {
ResultSetMetaData metaData = resultSet.getMetaData();
int columnCount = metaData.getColumnCount();
Map<String, Object> resultsMap = new HashMap<>();
for (int i = 1; i <= columnCount; ++i) {
String columnName = metaData.getColumnName(i).toLowerCase();
Object object = resultSet.getObject(i);
resultsMap.put(columnName, object);
}
return resultsMap;
}
private final String queryString;
protected Connection connection;
}
在Servlet中使用它把Java泛型成JSON字符串的com.fasterxml.jackson.databind.ObjectMapper我转换列表为JSON。
In the servlet I convert the List into JSON using the com.fasterxml.jackson.databind.ObjectMapper which converts Java Generics into a JSON String.
Connection connection = null;
try {
connection = DataSourceSingleton.getConnection();
EntityFactory nutrientEntityFactory = new EntityFactory(connection, NUTRIENT_QUERY_STRING);
List<Map<String, Object>> nutrients = nutrientEntityFactory.findMultiple(new Object[]{});
ObjectMapper mapper = new ObjectMapper();
String json = mapper.writeValueAsString(nutrients);
response.setContentType("application/json;charset=UTF-8");
response.getWriter().write(json);
} catch (SQLException e) {
throw new ServletException(e);
} finally {
if (connection != null) {
try {
connection.close();
} catch (SQLException e) {
throw new ServletException(e);
}
}
}
您可以传递参数preparedStatement是这样的:
You can pass in Parameters to the PreparedStatement like this:
String name = request.getHeader("name");
EntityFactory entityFactory = new EntityFactory(DataSourceSingleton.getConnection(), QUERY_STRING);
Map<String, Object> object = entityFactory.findSingle(new String[]{name});
private static final String QUERY_STRING = "SELECT NAME, PASSWORD, TOKEN, TOKEN_EXPIRATION FROM USER WHERE NAME = ?";
}
这篇关于如何转换成一个Java的ResultSet成JSON?的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!