我正在尝试取两张桌子＆＃39;数据并将其存储在json文件中。 Node _ test包含50000条记录和Node_contains 249762条记录。
当我在代码中读取记录时，Eclipse会关闭或出现内存异常错误。
如何优化下面的代码，以便我可以获取数据并将其写入json文件？
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Map;
import java.util.Random;
import java.util.Set;
import java.util.Map.Entry;
import java.util.Properties;
import javax.sql.DataSource;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonElement;
import com.google.gson.JsonParser;
import com.google.gson.JsonStreamParser;
import com.mysql.jdbc.jdbc2.optional.MysqlDataSource;
public class generateJsonFile {
private static final String jsonFilePath ="D:/Assignments/Sequence/myfile.json";
private static Set set = new HashSet();
public static DataSource getMySQLDataSource() throws Exception {
Properties props = new Properties();
FileInputStream fis = null;
MysqlDataSource mysqlDS = null;
try {
fis = new FileInputStream("D:/Assignments/Sequence/db.properties");
} catch (FileNotFoundException e) {
e.printStackTrace();
}
props.load(fis);
mysqlDS = new MysqlDataSource();
mysqlDS.setURL(props.getProperty("MYSQL_DB_URL"));
mysqlDS.setUser(props.getProperty("MYSQL_DB_USERNAME"));
mysqlDS.setPassword(props.getProperty("MYSQL_DB_PASSWORD"));
return mysqlDS;
}
//Generating x, y coordinates
/*public static String getRandomValue(final Random random,
final int lowerBound,
final int upperBound,
final int decimalPlaces)
{
if(lowerBound < 0 || upperBound <= lowerBound || decimalPlaces < 0){
throw new IllegalArgumentException("Put error message here");
}
final double dbl =
((random == null ? new Random() : random).nextDouble() //
* (upperBound - lowerBound))
+ lowerBound;
return String.format("%." + decimalPlaces + "f", dbl);
}*/
//Calling function for x & y coordinates
static String val;
public static String generateCoordinate(int count)
{
ArrayList al = new ArrayList(set);
System.out.println("size of set is ::"+set.size());
Iterator it = al.iterator();
while(it.hasNext())
{
return((String)al.get(count));
}
return null;
}
//create ID for edge
static StringBuffer sb;
static int temp = 1;
static String edgeID;
private static String createID()
{
sb = new StringBuffer("e");
for(int i = 1;i<=249762;i++)
{
if(i==temp)
{
edgeID=(sb.append(String.valueOf(i))).toString();
}
}
temp = temp+1;
return edgeID;
}
//function to set the color of node
private static String[] color_code = {"rgb(153,255,255)","rgb(0,204,204)","rgb(255,204,102)","rgb(255,51,51)","rgb(153,255,0)","rgb(102,255,102)","rgb(102,102,0)","rgb(255,255,51)","rgb(0,153,0)","rgb(102,0,102)","rgb(153,0,0)","rgb(255,153,153)"};
static Random ran = new Random();
private static String ColorPicker(){
int maximum = 11;
int minimum = 1;
int range = maximum - minimum + 1;
int index = ran.nextInt(range) + minimum;
System.out.println("color code: "+color_code[index]);
return color_code[index];
}
private static String getValue()
{
return null;
}
public static void main(String[] args) throws Exception {
Connection con = null;
PreparedStatement pst = null;
PreparedStatement pst1 = null;
ResultSet rs = null;
ResultSet rs1 = null;
HashMap hm = new HashMap();
HashMap hm1 = null;
//HashMap hm2 = null;
FileWriter fw = new FileWriter(jsonFilePath);
ArrayList nodesList = new ArrayList();
ArrayList edgeList = new ArrayList();
hm.put("nodes", nodesList);
hm.put("edges", edgeList);
final Random rnd = new Random();
/*for(int low = 0; low <10000; low++)Change 100 to 1000
{
String ran = getRandomValue(rnd, 0, 10, 4);
set.add(ran);
}*/
try {
con = getMySQLDataSource().getConnection();
pst = con.prepareStatement("select node_id, node_description,x_coordinate,y_coordinate from test.nodes_test;");
//pst.setMaxRows(100);
rs = pst.executeQuery();
while(rs.next()){
hm1 = new HashMap();
hm1.put("id",rs.getString("node_id"));
hm1.put("label",rs.getString("node_description"));
hm1.put("size", 0.1);
hm1.put("x", rs.getString("x_coordinate"));
hm1.put("y", rs.getString("y_coordinate"));
hm1.put("color", ColorPicker());
nodesList.add(hm1);
}
pst1 = con.prepareStatement("select node_id, dest_id from test.nodes_connection;");
//pst1.setMaxRows(10);
rs1 = pst1.executeQuery();
while(rs1.next()){
hm1 = new HashMap();
hm1.put("id", createID());
hm1.put("source",rs1.getString("node_id"));
hm1.put("target",rs1.getString("dest_id"));
hm1.put("type", "curve");
edgeList.add(hm1);
}
String json_string = new Gson().toJson(hm);
System.out.println(json_string);
JsonParser parser = new JsonParser();
Gson gs = new GsonBuilder().setPrettyPrinting().create();
JsonElement el = parser.parse(json_string);
json_string = gs.toJson(el);
try {
fw.append(json_string);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println("File written successfully..");
fw.close();
} catch (SQLException e) {
e.printStackTrace();
}finally{
try {
if(rs != null) rs.close();
if(pst != null) pst.close();
if(pst1 != null) pst1.close();
if(con != null) con.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
答案 0 :(得分：2)
尝试在eclipse.ini文件
-vmargs
-Dosgi.requiredJavaVersion=1.5
-Xms40m
-Xmx512m
您可以更改此类内容
-vmargs
-Dosgi.requiredJavaVersion=1.5
-Xms512m
-Xmx1024m
-XX:PermSize=256M
-XX:MaxPermSize=512M
这应该会停止崩溃（至少当我遇到这个问题时它对我有用）
答案 1 :(得分：0)
我不知道是否有人会检查您的代码并实际优化它，但您可以尝试增加Eclipse的堆大小。
在您的eclipse文件夹中打开eclipse.ini并将-Xmx512m更改为更大的值。说-Xmx2048m。
否则，请停止在内存中存储大量数据。