因此，我编写了一个在“ for”循环中将字符串写入文件的类，但是我无法使用Java中的BufferedWriter或PrintWriter将字符串内容写入文件。该文件在本地目录中创建，但是没有任何内容写入该文件。似乎是什么引起了麻烦？
代码是
package pmidtomeshConverter;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.io.StringWriter;
import java.net.URL;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.List;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import org.json.XML;
import org.w3c.dom.Document;
import org.xml.sax.SAXException;
public class Convert2MeSH {
public static void main(String[] args) throws JSONException, IOException, ParserConfigurationException, SAXException, TransformerException {
BufferedWriter writer = new BufferedWriter(new FileWriter("pathToALocalDirectory/pmidMESH.txt", true));
writer.write("at least this writes"); // This does not write either
JSONObject jsonPMIDlist = readJsonFromUrl("https://eutils.ncbi.nlm.nih.gov/entrez/eutils/esearch.fcgi?db=pubmed&retmode=json&retmax=1000&term=Physiotherapy%5d+OR+Rehabilitation");
JSONArray pmids = new JSONArray();
pmids = jsonPMIDlist.getJSONObject("esearchresult").getJSONArray("idlist");
for(int i=0; i<pmids.length();i++){
String baseURL = "https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&retmode=xml&rettype=abstract&id=";
String indPMID = pmids.get(i).toString();
Document doc = parseXML(new URL(baseURL + indPMID));
String xmlString = xml2String(doc);
// Converts the XML string into JSON
JSONObject jsonWithMeSH = XML.toJSONObject(xmlString);
JSONObject ind_MeSH = jsonWithMeSH.getJSONObject("PubmedArticleSet").getJSONObject("PubmedArticle").getJSONObject("MedlineCitation");
List<String> list_MeSH = new ArrayList<String>();
if (ind_MeSH.has("MeshHeadingList")) {
for (int j = 0; j < ind_MeSH.getJSONObject("MeshHeadingList").getJSONArray("MeshHeading").length(); j++) {
list_MeSH.add(ind_MeSH.getJSONObject("MeshHeadingList").getJSONArray("MeshHeading").getJSONObject(j).getJSONObject("DescriptorName").get("content").toString());
}
} else {
list_MeSH.add("null");
}
System.out.println(indPMID + ":" + String.join("\t", list_MeSH));
writer.append(indPMID + ":" + String.join("\t", list_MeSH)); // This does not write to the file either
}
writer.flush();
writer.close();
}
private static String xml2String(Document doc) throws TransformerException {
TransformerFactory transfac = TransformerFactory.newInstance();
Transformer trans = transfac.newTransformer();
trans.setOutputProperty(OutputKeys.METHOD, "xml");
trans.setOutputProperty(OutputKeys.INDENT, "yes");
trans.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", Integer.toString(2));
StringWriter sw = new StringWriter();
StreamResult result = new StreamResult(sw);
DOMSource source = new DOMSource(doc.getDocumentElement());
trans.transform(source, result);
String xmlString = sw.toString();
return xmlString;
}
private static Document parseXML(URL url) throws ParserConfigurationException, SAXException, IOException {
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
Document doc = db.parse((url).openStream());
doc.getDocumentElement().normalize();
return doc;
}
private static String readAll(Reader rd) throws IOException {
StringBuilder sb = new StringBuilder();
int cp;
while ((cp = rd.read()) != -1) {
sb.append((char) cp);
}
return sb.toString();
}
public static JSONObject readJsonFromUrl(String url) throws IOException, JSONException {
InputStream is = new URL(url).openStream();
try {
BufferedReader rd = new BufferedReader(new InputStreamReader(is, Charset.forName("UTF-8")));
String jsonText = readAll(rd);
JSONObject json = new JSONObject(jsonText);
return json;
} finally {
is.close();
}
}
“ System.out.println（indPMID +”：“ + String.join（” \ t“，list_MeSH））;的输出；”是，
答案 0 :(得分：0)
所以我制定了一个绕道解决方案。我知道for循环中的任何内容都没有写入文件，而且我也不知道为什么内容没有附加到文件中。
解决方案：首先，在循环中，我将内容写入Hashmap，然后在for循环之外，使用序列化将Hashmap写入文件。效果很好。
这是代码，
package pmidtomeshConverter;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.Reader;
import java.io.StringWriter;
import java.net.URL;
import java.nio.charset.Charset;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Properties;
import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import org.json.XML;
import org.w3c.dom.Document;
import org.xml.sax.SAXException;
import com.google.common.collect.ArrayListMultimap;
import com.google.common.collect.Multimap;
public class Convert2MeSH {
public static void main(String[] args) {
//BufferedWriter writer = new BufferedWriter(new FileWriter("/home/anjani/eclipse-workspace/pmidtomeshConverter/src/main/resources/outputFiles/pmidMESH.txt", true));
//Universal Multimap to store the values
Map<String, String> universalMeSHMap = new HashMap<String, String>();
FileOutputStream fs;
BufferedWriter writer;
try {
fs = new FileOutputStream("/home/anjani/eclipse-workspace/pmidtomeshConverter/src/main/resources/outputFiles/pmidMESH.txt");
OutputStreamWriter ow = new OutputStreamWriter(fs);
writer = new BufferedWriter(ow);
JSONObject jsonPMIDlist = readJsonFromUrl("https://eutils.ncbi.nlm.nih.gov/entrez/eutils/esearch.fcgi?db=pubmed&retmode=json&retmax=1000&term=Physiotherapy%5d+OR+Rehabilitation");
JSONArray pmids = new JSONArray();
pmids = jsonPMIDlist.getJSONObject("esearchresult").getJSONArray("idlist");
for(int i=0; i<pmids.length();i++){
String baseURL = "https://eutils.ncbi.nlm.nih.gov/entrez/eutils/efetch.fcgi?db=pubmed&retmode=xml&rettype=abstract&id=";
String indPMID = pmids.get(i).toString();
Document doc = parseXML(new URL(baseURL + indPMID));
// Converts xml from doc into a string
String xmlString = xml2String(doc);
// Converts the xml-string into JSON
JSONObject jsonWithMeSH = XML.toJSONObject(xmlString);
JSONObject ind_MeSH = jsonWithMeSH.getJSONObject("PubmedArticleSet").getJSONObject("PubmedArticle").getJSONObject("MedlineCitation");
List<String> list_MeSH = new ArrayList<String>();
if (ind_MeSH.has("MeshHeadingList")) {
for (int j = 0; j < ind_MeSH.getJSONObject("MeshHeadingList").getJSONArray("MeshHeading").length(); j++) {
list_MeSH.add(ind_MeSH.getJSONObject("MeshHeadingList").getJSONArray("MeshHeading").getJSONObject(j).getJSONObject("DescriptorName").get("content").toString());
}
} else {
list_MeSH.add("null");
}
System.out.println(indPMID + ":" + String.join("\t", list_MeSH));
// instead of writing to a file, the content is stored in a HashMap
universalMeSHMap.put(indPMID, String.join("\t", list_MeSH));
}
// Writing the HashMap to the file (This is the answer)
for (Map.Entry<String,String> entry : universalMeSHMap.entrySet()) {
writer.append(entry.getKey() + ":" + entry.getValue() + "\n");
}
writer.flush();
writer.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ParserConfigurationException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SAXException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (TransformerException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
private static String xml2String(Document doc) throws TransformerException {
TransformerFactory transfac = TransformerFactory.newInstance();
Transformer trans = transfac.newTransformer();
trans.setOutputProperty(OutputKeys.METHOD, "xml");
trans.setOutputProperty(OutputKeys.INDENT, "yes");
trans.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", Integer.toString(2));
StringWriter sw = new StringWriter();
StreamResult result = new StreamResult(sw);
DOMSource source = new DOMSource(doc.getDocumentElement());
trans.transform(source, result);
String xmlString = sw.toString();
return xmlString;
}
private static Document parseXML(URL url) throws ParserConfigurationException, SAXException, IOException {
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
DocumentBuilder db = dbf.newDocumentBuilder();
Document doc = db.parse((url).openStream());
doc.getDocumentElement().normalize();
return doc;
}
private static String readAll(Reader rd) throws IOException {
StringBuilder sb = new StringBuilder();
int cp;
while ((cp = rd.read()) != -1) {
sb.append((char) cp);
}
return sb.toString();
}
public static JSONObject readJsonFromUrl(String url) throws IOException, JSONException {
InputStream is = new URL(url).openStream();
try {
BufferedReader rd = new BufferedReader(new InputStreamReader(is, Charset.forName("UTF-8")));
String jsonText = readAll(rd);
JSONObject json = new JSONObject(jsonText);
return json;
} finally {
is.close();
}
}}
结果文件看起来是这样的，
