如何使用 Java 从 json 数据生成 csv 文件？
How to generated the csv file from json data with Java?
我尝试从 json 类型的数据生成 csv 文件。这些是我的 json 测试数据。
{
"realtime_start":"2020-09-25",
"realtime_end":"2020-09-25",,
"units": "Percent",
"seriess": [
{
"name": "James",
"age": 29,
"house": "CA"
},
{
"name": "Jina",
"age": 39,
"house": "MA",
"notes": "Million tonne punch"
},
}
问题是 json 数组类型 "seriess" 不包含所有节点中的 "notes" 节点。
我制作了以下 java 代码以将此 json 数据更改为具有 header 列
的 csv 文件
JSONObject json = getJsonFileFromURL(...)
JSONArray docsArray = json.getJSONArray("seriess");
docsArray.put(json.get("realtime_start"));
docsArray.put(json.get("realtime_end"));
docsArray.put(json.get("units"));
JsonNode jsonTree = new ObjectMapper().readTree(docsArray.toString());
Builder csvSchemaBuilder = CsvSchema.builder();
for(JsonNode node : jsonTree) {
node.fieldNames().forEachRemaining(fieldName -> {csvSchemaBuilder.addColumn(fieldName);} );
}
CsvSchema csvSchema = csvSchemaBuilder.build().withHeader();
CsvMapper csvMapper = new CsvMapper();
csvMapper.writerFor(JsonNode.class).with(csvSchema).writeValue(new File("test.csv"), jsonTree);
但是错误的结果如下所示，
realtime_start,realtime_end,units,names,age,house,realtime_start,realtime_end,units,names,age,house,notes, realtime_start,.....
生成的 header 列不包含不同的值。 header 列一式两份添加。如何生成如下所示的不同 header
realtime_start,realtime_end,units,names,age,house, notes
有什么想法吗？
更新部分
我尝试从 FRED（圣路易斯联邦储备银行）提取数据。 FRED提供简单方便的Python api如下，
from fredapi import Fred
import pandas as pd
fred = Fred(api_key='abcdefghijklmnopqrstuvwxyz0123456789')
data_unemploy = fred.search('Unemployment Rate in California')
data_unemploy.to_csv("test_unemploy.csv")
但是 java api 已被弃用，所以我必须开发简单的 Java api 将 json 值转换为 csv 文件。我通过谷歌搜索
找到了以下 Java 代码
JSONObject json = getJsonFileFromURL("https://api.stlouisfed.org/fred/series/search?search_text=Unemployment+Rate+in+California&api_key=abcdefghijklmnopqrstuvwxyz0123456789&file_type=json");
JSONArray docsArray = json.getJSONArray("seriess");
docsArray.put(json.get("realtime_start"));
docsArray.put(json.get("realtime_end"));
JsonNode jsonTree = new ObjectMapper().readTree(docsArray.toString());
JsonNode firstObject = jsonTree.elements().next(); // I am struggling with this line
firstObject.fieldNames().forEachRemaining(fieldName -> {csvSchemaBuilder.addColumn(fieldName);} );
CsvSchema csvSchema = csvSchemaBuilder.build().withHeader();
CsvMapper csvMapper = new CsvMapper();
csvMapper.writerFor(JsonNode.class).with(csvSchema).writeValue(new File("test.csv"), jsonTree);
要从 json 数据 JsonNode firstObject = jsonTree.elements().next(); return 第一个 json 节点中提取列。但是这一行没有returnnotes列。因为第一行不包含 notes 键值。
所以我将此代码行更改为以下行
for(JsonNode node : jsonTree) {
node.fieldNames().forEachRemaining(fieldName -> {
csvSchemaBuilder.addColumn(fieldName);
} );
}
但是这些行抛出了我不期望的结果。像下面这样重复的重复列
realtime_start,realtime_end,units,names,age,house,realtime_start,realtime_end,units,names,age,house,notes, realtime_start,.....
我完全被这部分卡住了。
您可以使用 Apache Commons IO 库来做到这一点
pom.xml
<dependency>
<groupId>commons-io</groupId>
<artifactId>commons-io</artifactId>
<version>2.6</version>
</dependency>
ConvertJsonToCSVTest.java
import java.io.File;
import org.apache.commons.io.FileUtils;
import org.json.*;
public class ConvertJsonToCSVTest {
public static void main(String[] args) throws JSONException {
String jsonArrayString = "{\"fileName\": [{\"first name\": \"Adam\",\"last name\": \"Smith\",\"location\": \"London\"}]}";
JSONObject output;
try {
output = new JSONObject(jsonArrayString);
JSONArray docs = output.getJSONArray("fileName");
File file = new File("EmpDetails.csv");
String csv = CDL.toString(docs);
FileUtils.writeStringToFile(file, csv);
System.out.println("Data has been Sucessfully Writeen to "+ file);
System.out.println(csv);
}
catch(Exception e) {
e.printStackTrace();
}
}
}
输出
Data has been Sucessfully Writeen to EmpDetails.csv
last name,first name,location
Smith,Adam,London
很可能最简单的写一个 bin 类型 class 如下：
public class CsvVo {
private String realtime_start;
private String realtime_end;
private String units;
private String name;
private String age;
private String house;
private String notes;
public void setRealtime_start(String realtime_start) {
this.realtime_start = realtime_start;
}
//Other getters and Setters
然后你可以写:
public class ConvertJsonToCSVTest {
public static void main(String[] args) throws JSONException {
String jsonArrayString = "{\n" +
"\t\"realtime_start\": \"2020-09-25\",\n" +
"\t\"realtime_end\": \"2020-09-25\",\n" +
"\t\"units\": \"Percent\",\n" +
"\t\"seriess\": [{\n" +
"\t\t\t\"name\": \"James\",\n" +
"\t\t\t\"age\": 29,\n" +
"\t\t\t\"house\": \"CA\"\n" +
"\t\t},\n" +
"\t\t{\n" +
"\t\t\t\"name\": \"Jina\",\n" +
"\t\t\t\"age\": 39,\n" +
"\t\t\t\"house\": \"MA\",\n" +
"\t\t\t\"notes\": \"Million tonne punch\"\n" +
"\t\t}\n" +
"\t]\n" +
"}";
JSONObject inJson;
List<CsvVo> list = new ArrayList<>();
inJson = new JSONObject(jsonArrayString);
JSONArray inJsonSeries = inJson.getJSONArray("seriess");
for (int i = 0, size = inJsonSeries.length(); i < size; i++){
CsvVo line = new CsvVo();
line.setRealtime_start(inJson.get("realtime_start").toString());
line.setRealtime_end(inJson.get("realtime_end").toString());
line.setUnits(inJson.get("units").toString());
JSONObject o = (JSONObject)inJsonSeries.get(i);
line.setName(o.get("name").toString());
line.setAge(o.get("age").toString());
line.setHouse(o.get("house").toString());
try {
line.setNotes(o.get("notes").toString());
}catch (JSONException e){
line.setNotes("");
}
list.add(line);
}
String[] cols = {"realtime_start", "realtime_end", "units", "name", "age", "house", "notes"};
CsvUtils.csvWriterUtil(CsvVo.class, list, "in/EmpDetails.csv", cols);
}
}
csvWriterUtil 如下所示：
public static <T> void csvWriterUtil(Class<T> beanClass, List<T> data, String outputFile, String[] columnMapping){
try{
Writer writer = new BufferedWriter(new FileWriter(outputFile));
ColumnPositionMappingStrategy<T> strategy = new ColumnPositionMappingStrategy<>();
strategy.setType(beanClass);
strategy.setColumnMapping(columnMapping);
StatefulBeanToCsv<T> statefulBeanToCsv =new StatefulBeanToCsvBuilder<T>(writer)
.withMappingStrategy(strategy)
.build();
writer.write(String.join(",",columnMapping)+"\n");
statefulBeanToCsv.write(data);
writer.close();
} catch (IOException e) {
e.printStackTrace();
} catch (CsvRequiredFieldEmptyException e) {
e.printStackTrace();
} catch (CsvDataTypeMismatchException e) {
e.printStackTrace();
}
}
完整示例可在 GitRepo
中找到
我尝试从 json 类型的数据生成 csv 文件。这些是我的 json 测试数据。
{
"realtime_start":"2020-09-25",
"realtime_end":"2020-09-25",,
"units": "Percent",
"seriess": [
{
"name": "James",
"age": 29,
"house": "CA"
},
{
"name": "Jina",
"age": 39,
"house": "MA",
"notes": "Million tonne punch"
},
}
问题是 json 数组类型 "seriess" 不包含所有节点中的 "notes" 节点。
我制作了以下 java 代码以将此 json 数据更改为具有 header 列
JSONObject json = getJsonFileFromURL(...)
JSONArray docsArray = json.getJSONArray("seriess");
docsArray.put(json.get("realtime_start"));
docsArray.put(json.get("realtime_end"));
docsArray.put(json.get("units"));
JsonNode jsonTree = new ObjectMapper().readTree(docsArray.toString());
Builder csvSchemaBuilder = CsvSchema.builder();
for(JsonNode node : jsonTree) {
node.fieldNames().forEachRemaining(fieldName -> {csvSchemaBuilder.addColumn(fieldName);} );
}
CsvSchema csvSchema = csvSchemaBuilder.build().withHeader();
CsvMapper csvMapper = new CsvMapper();
csvMapper.writerFor(JsonNode.class).with(csvSchema).writeValue(new File("test.csv"), jsonTree);
但是错误的结果如下所示，
realtime_start,realtime_end,units,names,age,house,realtime_start,realtime_end,units,names,age,house,notes, realtime_start,.....
生成的 header 列不包含不同的值。 header 列一式两份添加。如何生成如下所示的不同 header
realtime_start,realtime_end,units,names,age,house, notes
有什么想法吗？
更新部分
我尝试从 FRED（圣路易斯联邦储备银行）提取数据。 FRED提供简单方便的Python api如下，
from fredapi import Fred
import pandas as pd
fred = Fred(api_key='abcdefghijklmnopqrstuvwxyz0123456789')
data_unemploy = fred.search('Unemployment Rate in California')
data_unemploy.to_csv("test_unemploy.csv")
但是 java api 已被弃用，所以我必须开发简单的 Java api 将 json 值转换为 csv 文件。我通过谷歌搜索
找到了以下 Java 代码JSONObject json = getJsonFileFromURL("https://api.stlouisfed.org/fred/series/search?search_text=Unemployment+Rate+in+California&api_key=abcdefghijklmnopqrstuvwxyz0123456789&file_type=json");
JSONArray docsArray = json.getJSONArray("seriess");
docsArray.put(json.get("realtime_start"));
docsArray.put(json.get("realtime_end"));
JsonNode jsonTree = new ObjectMapper().readTree(docsArray.toString());
JsonNode firstObject = jsonTree.elements().next(); // I am struggling with this line
firstObject.fieldNames().forEachRemaining(fieldName -> {csvSchemaBuilder.addColumn(fieldName);} );
CsvSchema csvSchema = csvSchemaBuilder.build().withHeader();
CsvMapper csvMapper = new CsvMapper();
csvMapper.writerFor(JsonNode.class).with(csvSchema).writeValue(new File("test.csv"), jsonTree);
要从 json 数据 JsonNode firstObject = jsonTree.elements().next(); return 第一个 json 节点中提取列。但是这一行没有returnnotes列。因为第一行不包含 notes 键值。
所以我将此代码行更改为以下行
for(JsonNode node : jsonTree) {
node.fieldNames().forEachRemaining(fieldName -> {
csvSchemaBuilder.addColumn(fieldName);
} );
}
但是这些行抛出了我不期望的结果。像下面这样重复的重复列
realtime_start,realtime_end,units,names,age,house,realtime_start,realtime_end,units,names,age,house,notes, realtime_start,.....
我完全被这部分卡住了。
您可以使用 Apache Commons IO 库来做到这一点
pom.xml
<dependency>
<groupId>commons-io</groupId>
<artifactId>commons-io</artifactId>
<version>2.6</version>
</dependency>
ConvertJsonToCSVTest.java
import java.io.File;
import org.apache.commons.io.FileUtils;
import org.json.*;
public class ConvertJsonToCSVTest {
public static void main(String[] args) throws JSONException {
String jsonArrayString = "{\"fileName\": [{\"first name\": \"Adam\",\"last name\": \"Smith\",\"location\": \"London\"}]}";
JSONObject output;
try {
output = new JSONObject(jsonArrayString);
JSONArray docs = output.getJSONArray("fileName");
File file = new File("EmpDetails.csv");
String csv = CDL.toString(docs);
FileUtils.writeStringToFile(file, csv);
System.out.println("Data has been Sucessfully Writeen to "+ file);
System.out.println(csv);
}
catch(Exception e) {
e.printStackTrace();
}
}
}
输出
Data has been Sucessfully Writeen to EmpDetails.csv
last name,first name,location
Smith,Adam,London
很可能最简单的写一个 bin 类型 class 如下：
public class CsvVo {
private String realtime_start;
private String realtime_end;
private String units;
private String name;
private String age;
private String house;
private String notes;
public void setRealtime_start(String realtime_start) {
this.realtime_start = realtime_start;
}
//Other getters and Setters
然后你可以写:
public class ConvertJsonToCSVTest {
public static void main(String[] args) throws JSONException {
String jsonArrayString = "{\n" +
"\t\"realtime_start\": \"2020-09-25\",\n" +
"\t\"realtime_end\": \"2020-09-25\",\n" +
"\t\"units\": \"Percent\",\n" +
"\t\"seriess\": [{\n" +
"\t\t\t\"name\": \"James\",\n" +
"\t\t\t\"age\": 29,\n" +
"\t\t\t\"house\": \"CA\"\n" +
"\t\t},\n" +
"\t\t{\n" +
"\t\t\t\"name\": \"Jina\",\n" +
"\t\t\t\"age\": 39,\n" +
"\t\t\t\"house\": \"MA\",\n" +
"\t\t\t\"notes\": \"Million tonne punch\"\n" +
"\t\t}\n" +
"\t]\n" +
"}";
JSONObject inJson;
List<CsvVo> list = new ArrayList<>();
inJson = new JSONObject(jsonArrayString);
JSONArray inJsonSeries = inJson.getJSONArray("seriess");
for (int i = 0, size = inJsonSeries.length(); i < size; i++){
CsvVo line = new CsvVo();
line.setRealtime_start(inJson.get("realtime_start").toString());
line.setRealtime_end(inJson.get("realtime_end").toString());
line.setUnits(inJson.get("units").toString());
JSONObject o = (JSONObject)inJsonSeries.get(i);
line.setName(o.get("name").toString());
line.setAge(o.get("age").toString());
line.setHouse(o.get("house").toString());
try {
line.setNotes(o.get("notes").toString());
}catch (JSONException e){
line.setNotes("");
}
list.add(line);
}
String[] cols = {"realtime_start", "realtime_end", "units", "name", "age", "house", "notes"};
CsvUtils.csvWriterUtil(CsvVo.class, list, "in/EmpDetails.csv", cols);
}
}
csvWriterUtil 如下所示：
public static <T> void csvWriterUtil(Class<T> beanClass, List<T> data, String outputFile, String[] columnMapping){
try{
Writer writer = new BufferedWriter(new FileWriter(outputFile));
ColumnPositionMappingStrategy<T> strategy = new ColumnPositionMappingStrategy<>();
strategy.setType(beanClass);
strategy.setColumnMapping(columnMapping);
StatefulBeanToCsv<T> statefulBeanToCsv =new StatefulBeanToCsvBuilder<T>(writer)
.withMappingStrategy(strategy)
.build();
writer.write(String.join(",",columnMapping)+"\n");
statefulBeanToCsv.write(data);
writer.close();
} catch (IOException e) {
e.printStackTrace();
} catch (CsvRequiredFieldEmptyException e) {
e.printStackTrace();
} catch (CsvDataTypeMismatchException e) {
e.printStackTrace();
}
}
完整示例可在 GitRepo
中找到